**Criteria of Determination of Safe Grain Storage Time – A Review**

Agnieszka Kaleta and Krzysztof Górnicki

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/52235

## **1. Introduction**

[32] Stepniewski, A, & Szot, B. Postharvest operations and quality of rapeseed. Proceed‐ ings of 9th. International Rapeseed Congress, Cambridge, England (1995). I, ,

[33] Stepniewski, A, & Szot, B. Quality of rapeseed in postharvest handling. Preprints of workshop on Control Applications in Post-Harvest and Processing Technology,

[34] Stepniewski, A, Szot, B, Fornal, J, & Sadowska, J. Drying conditions and mechanical

[35] Szot, B, & Stepniewski, A. Studies on mechanical properties of rape in the aspect of its quantity and quality losses. Zemedelska Technika, (1995). , 1995(41), 133-136.

[36] Szot, B, Stepniewski, A, Dobrzanski, B, & Rybczynski, R. The influence of higher temperature of rapeseeds on their mechanical resistance. Proceedings of th. Interna‐ tional Conference Physical Properties of Agricultural Materials and Their Influence

[37] White, G. M, Bridges, T. C, Loewer, O. J, & Ross, I. J. (1980). Seed coat damage in

on Technological Processes, Rostock, Germany, (1989). s. 815- 818, 4.

thin-layer drying of soybeans. Trans. ASAE , 23(1), 224-227.

properties of rapeseed. J. Food Physics, (1994). , 1994, 86-89.

232-234.

294 Advances in Agrophysical Research

CAPPT'95, Ostend, Belgium (1995).

Cereals, before being consumed as food, go through the process of cultivation, harvesting, drying, preparation and marketing (including storage) all under natural conditions, and therefore, often involve microbiological contamination and infection (Abdullah et al., 2000).

Therefore it can be stated that grain starts deteriorating from the time of harvest, due to in‐ teractions between the physical, chemical and biological variables within the environment (Mason et al., 1997). Cereal grains just after being harvested contain microbial contamination coming from several sources, such as dust, water, ill plants, insects, solid, fertilisers and ani‐ mal feces. Bacteria found in grains mainly belong to the families *Pseudomonadaceae*, *Micrococ‐ caceae*, *Lactobacillaceae* and *Bacillaceae*, and moulds are mostly *Alternaria*, *Fusarium*, *Helminthosorium* and *Cladosporium*, although other genus can also be present. The microbial composition of the cereals is of great importance for the storage of grains, since at high mois‐ ture levels the microorganisms could grow and alter the properties of product (Laca et al., 2006). Grain deterioration is also related to respiration of the grain itself and of the accompa‐ nying microorganisms. The evolution of carbon dioxide, water and heat is associated with this respiration or deterioration (Steele et al., 1969).

A 13 % moisture content is considered to be the maximum value for the storage of wheat, corn, barley and rice during short periods, though temperature and oxygen concentration also play an important role (Laca et al., 2006).

Harvesting high moisture grain such as wheat, corn or rice has become, however, common practice to protect the grain from wet weather conditions which can cause weathering and mould infection of grain in the field. High moisture grain is susceptible to deterioration by microorganisms and hence should be dried before unacceptable quality loss occurs. A

knowledge of deterioration rates of high moisture grain under various storage conditions would help farmers and grain managers to know how quickly to dry the grain or adjust the storage conditions to prevent further quality loss (Kakunakaran et al., 2001). It is generally accepted that 5-15 % of the total weight of all cereals, oilseeds, and pulses is lost after har‐ vest (Padin et al., 2002). Improved storage conditions would allow a 10 – 20 % increase in the supply of food available to people (Christiansen and Kaufmann, 1969).

evolution of 14.7 g of carbon dioxide per kg of grain matter. Therefore respiration rate is closely related to grain dry matter loss and, consequently, global quality loss. Modelling CO2 production can be used to simplify the prediction of rate of quality loss, assuming pre‐

Contamination of harvested grain by microorganisms is natural and permanent. In temper‐ ate climates with medium wet or moist grain at harvest, the genera *Fusarium*, *Alternaria* and *Helmintosporium* (called "field flora") are predominant. During long term storage, xerophilic fungi of the genera *Aspergillus* and *Penicillium* (called "storage flora") progressively replace the "field flora" over a period of several months of storage. At 15-19 % moisture content, most species of the field flora are inhibited or die whereas storage flora species slowly grow (Fleurat-Lessard, 2002; Frisvad, 1995; Pelhate, 1988). Since the respiratory processes of mi‐ croorganisms or of hidden insect infestation are similar to those of the grain itself, the com‐ bustion of carbohydrates is a representation of grain, microorganisms and insect respiration

The following mathematical formulas for predicting carbon dioxide production and dry

White et al. (1982) carried out numerous experiments on the carbon dioxide release rates of wheat and developed the following equation for general prediction of the instant rate of CO2

where *X* is the rate of CO2 production in mg kg-1d. m. per 24-h period, *T* is the grain temper‐ ature in °C, *t* is the time in h, *Mw* is the grain moisture content in % w. b., and *a*, *b*, *c*, *d*, and *e*

where *X* is the rate of CO2 production in mg (100 gd. m.)-1 per 24-h period, *Mw* is the grain moisture content in % w. b., *T* is the grain temperature in °C, and *a*, *b*, and *c* are empirical

Karunakaran et al. (2001) determined the deterioration rate of wheat stored at 25°C by meas‐ uring the respiration rate of grain and microorganisms. The measured rates of CO2 produc‐ tion during storage at 17, 18, and 19 % m.c. wet basis were combined and fitted to the

<sup>2</sup> *X a bT ct dt eMw* =+ + + + (2)

Criteria of Determination of Safe Grain Storage Time – A Review

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297

*X aM bT c* = ++ exp( *<sup>w</sup>* ) (3)

<sup>2</sup> ln 15.56 0.21 0.004 1.08 *X ttMw* =- + - + (4)

dominantly aerobic respiration.

release from grain:

are empirical constants.

constants.

following equation:

(Fleurat-Lessard, 2002; Sinha et al., 1986; Steele et al., 1969).

matter loss can be found in the bibliography of the subject.

The following equation was developed by Srour (1988):

Grain quality is critical in today's grain trade because of more stringent food-safety de‐ mands and an increase in market competition, therefore to avoid spoilage of grain during storage it is necessary to determine the safe grain storage time.

Safe storage time is the period of exposure of a product at a particular moisture content to a particular relative humidity and temperature below which crop deterioration may occur and beyond which the crop may be impaired. To keep losses low, crops must be dried to the safe storage moisture content (i. e. moisture content required for long term storage) within the safe storage time (Ekechukwu, 1999). Determination of safe grain storage time is an an‐ swer to the following question: how long can grains of particular moisture content and tem‐ perature be stored without the risk of the quality deterioration (Ryniecki, 2006).

Knows in the bibliography of the subject are tables and graphs of the storage times. Some‐ times, however, mathematical formulas are more useful. They can be easily incorporated in‐ to the mathematical models of grain drying or aeration and expert systems which are aids for storage-grain management (Arinze et al., 1993; Courtois, 1995; Fleurat-Lessard, 2002; Ka‐ leta, 1996). Such formulas known in the bibliography of the subject and own formulas devel‐ oped by the authors of the chapter are presented in the paper.

To test the effect of grain parameters on the safe storage period, three criteria have been ap‐ plied: carbon dioxide (CO2) production and dry matter loss, appearance of visible moulds, and germination capacity.

## **2. Carbon dioxide production and dry matter loss**

Grain deterioration is related to respiration of the grain itself and of the accompanying mi‐ croorganisms. Respiration is the process of oxidizing (combusting) carbohydrates and yield‐ ing carbon dioxide, water vapour and energy. Therefore, respiration consumes dry matter.

The complete combustion (aerobic respiration) of a typical carbohydrate such as starch is represented by the following equation:

$$\rm C\_6H\_{12}O\_6 + 6O\_2 \to 6CO\_2 + 6H\_2O + heat \tag{1}$$

According to this equation during the breakdown of 1 g of dry matter by aerobic respiration using 1.07 g of oxygen, 1.47 g of carbon dioxide, 0.6 g of water, and 15.4 kJ of heat energy are released. It means that a 1 % loss in grain dry matter carbohydrate is accompanied by the evolution of 14.7 g of carbon dioxide per kg of grain matter. Therefore respiration rate is closely related to grain dry matter loss and, consequently, global quality loss. Modelling CO2 production can be used to simplify the prediction of rate of quality loss, assuming pre‐ dominantly aerobic respiration.

Contamination of harvested grain by microorganisms is natural and permanent. In temper‐ ate climates with medium wet or moist grain at harvest, the genera *Fusarium*, *Alternaria* and *Helmintosporium* (called "field flora") are predominant. During long term storage, xerophilic fungi of the genera *Aspergillus* and *Penicillium* (called "storage flora") progressively replace the "field flora" over a period of several months of storage. At 15-19 % moisture content, most species of the field flora are inhibited or die whereas storage flora species slowly grow (Fleurat-Lessard, 2002; Frisvad, 1995; Pelhate, 1988). Since the respiratory processes of mi‐ croorganisms or of hidden insect infestation are similar to those of the grain itself, the com‐ bustion of carbohydrates is a representation of grain, microorganisms and insect respiration (Fleurat-Lessard, 2002; Sinha et al., 1986; Steele et al., 1969).

The following mathematical formulas for predicting carbon dioxide production and dry matter loss can be found in the bibliography of the subject.

White et al. (1982) carried out numerous experiments on the carbon dioxide release rates of wheat and developed the following equation for general prediction of the instant rate of CO2 release from grain:

$$dX = a + bT + ct + dt^2 + eM\_w \tag{2}$$

where *X* is the rate of CO2 production in mg kg-1d. m. per 24-h period, *T* is the grain temper‐ ature in °C, *t* is the time in h, *Mw* is the grain moisture content in % w. b., and *a*, *b*, *c*, *d*, and *e* are empirical constants.

The following equation was developed by Srour (1988):

knowledge of deterioration rates of high moisture grain under various storage conditions would help farmers and grain managers to know how quickly to dry the grain or adjust the storage conditions to prevent further quality loss (Kakunakaran et al., 2001). It is generally accepted that 5-15 % of the total weight of all cereals, oilseeds, and pulses is lost after har‐ vest (Padin et al., 2002). Improved storage conditions would allow a 10 – 20 % increase in

Grain quality is critical in today's grain trade because of more stringent food-safety de‐ mands and an increase in market competition, therefore to avoid spoilage of grain during

Safe storage time is the period of exposure of a product at a particular moisture content to a particular relative humidity and temperature below which crop deterioration may occur and beyond which the crop may be impaired. To keep losses low, crops must be dried to the safe storage moisture content (i. e. moisture content required for long term storage) within the safe storage time (Ekechukwu, 1999). Determination of safe grain storage time is an an‐ swer to the following question: how long can grains of particular moisture content and tem‐

Knows in the bibliography of the subject are tables and graphs of the storage times. Some‐ times, however, mathematical formulas are more useful. They can be easily incorporated in‐ to the mathematical models of grain drying or aeration and expert systems which are aids for storage-grain management (Arinze et al., 1993; Courtois, 1995; Fleurat-Lessard, 2002; Ka‐ leta, 1996). Such formulas known in the bibliography of the subject and own formulas devel‐

To test the effect of grain parameters on the safe storage period, three criteria have been ap‐ plied: carbon dioxide (CO2) production and dry matter loss, appearance of visible moulds,

Grain deterioration is related to respiration of the grain itself and of the accompanying mi‐ croorganisms. Respiration is the process of oxidizing (combusting) carbohydrates and yield‐ ing carbon dioxide, water vapour and energy. Therefore, respiration consumes dry matter.

The complete combustion (aerobic respiration) of a typical carbohydrate such as starch is

According to this equation during the breakdown of 1 g of dry matter by aerobic respiration using 1.07 g of oxygen, 1.47 g of carbon dioxide, 0.6 g of water, and 15.4 kJ of heat energy are released. It means that a 1 % loss in grain dry matter carbohydrate is accompanied by the

C H O 6O 6CO 6H O heat 6 12 6 2 2 2 +® + + (1)

the supply of food available to people (Christiansen and Kaufmann, 1969).

perature be stored without the risk of the quality deterioration (Ryniecki, 2006).

storage it is necessary to determine the safe grain storage time.

oped by the authors of the chapter are presented in the paper.

**2. Carbon dioxide production and dry matter loss**

and germination capacity.

296 Advances in Agrophysical Research

represented by the following equation:

$$X = \exp\left(aM\_w + bT + c\right) \tag{3}$$

where *X* is the rate of CO2 production in mg (100 gd. m.)-1 per 24-h period, *Mw* is the grain moisture content in % w. b., *T* is the grain temperature in °C, and *a*, *b*, and *c* are empirical constants.

Karunakaran et al. (2001) determined the deterioration rate of wheat stored at 25°C by meas‐ uring the respiration rate of grain and microorganisms. The measured rates of CO2 produc‐ tion during storage at 17, 18, and 19 % m.c. wet basis were combined and fitted to the following equation:

$$
\ln X = -15.56 + 0.21t - 0.004t^2 + 1.08M\_w \tag{4}
$$

where*X* is the rate of CO2 production in mg d-1 kg-1d. m., *t* is the storage time in d, and *Mw* is the moisture content in % w. b.

periments were conducted *in vitro*. Maize at 14, 16, 18, 20 and 22 % m.c. was initially condi‐ tioned for 28 days in tightly wrapped plastic bags and then stored in sealed containers at 30°C for up to 75 days. Carbon dioxide produced within the containers replaced the oxygen. As the moisture content increased the time for O2 depletion shortened, from 600 h at 14 % m.c. to 12 h at 22 %. The maize at 20 and 22 % m.c. exhibited the highest DML (0.59 % and 0.74 % respectively after 75 days) and the maize at 14 and 16 % m.c. the lowest (0.02 % and 0.15 %). Adhikarinayake et al. (2006) found out that during airtight storage of 14 % m.c. pad‐ dy in a ferro-cement bin, oxygen concentration dropped to 2.7 % within 30 days and carbon dioxide rose to 9.1 %. After 6 months storage, DML was 0.4 %. Varnova et al. (1995) noted

When grain temperature and moisture content cannot be assumed constant for the entire

The values of the constants for long-grain rough rice used in the equations (5) and (6) were

Thompson (1972) took into account negative influence of mechanical damages on dry matter loss and obtained the following expression to determine the DML (in %) of shelled corn:

*MTD*

{ ( ) } 1.53 -1 <sup>2</sup> *M MM M <sup>M</sup>* 0.103 exp 455 100 0.845 1.558 for 0.149 0.538 kg H O·kg d.m. - <sup>=</sup> - + £ £ é ù

found to be (Seib et al., 1980): *A*=0.001889, *C*=0.7101, *D*=0.02740, *E*=31.63.

*r*

*<sup>t</sup> <sup>t</sup>*

( ) ( <sup>1</sup>) e e d DML d e e e *<sup>C</sup> <sup>y</sup> <sup>z</sup> <sup>y</sup> z x t ACt* - - <sup>=</sup> (6)

Criteria of Determination of Safe Grain Storage Time – A Review

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299

DML 0.0883 exp0.006 1 0.00102 ( ) *r r* = *t t* - + (7)

ê ú ë û (9)

32.3exp 3.48 0.03 0.53 for 15.6 C or 19% ( ) *M TTM T w* é ù £ ë û = - + £° (10)

32.3exp 3.48 0.03 0.53 0.01 19 exp 0.61 0.03 0.47 ( ) ( ) ( ) *M TM T T w* = -é ++ - <sup>ù</sup> ë û é ù - ë û (11)

*M MM* <sup>=</sup> × × (8)

storage time used, the method of rates was used to calculate DML (Freer et al., 1990):

that a sealed bulk of barley declined to 4 % O2 after 50 days.

where *x=AtC*, *y*=*D*(1.8 *T*-28), *z*=*E*(*Mw*-0.14)

where:

for T>15.6°C and 19<*Mw*≤28%

There are however some problems in using equations (2) - (4) to describe quality changes. They are based on the measurement of CO2 release rate, either from a grain sample or direct‐ ly in a grain bin. Such measurements can be done using sophisticated equipment and in lab‐ oratory conditions. Additionally, when grain moisture is below 14 % (w. b.) the release rate is very low and therefore it is very difficult to measure it. However, the above formulas are not useful in prediction the storage life.

Another option for the prediction of safe storage life is the calculation of dry matter loss (DML) as a function of grain temperature, grain moisture content, and storage time.

Seib et al. (1980) stated that the amount of dry matter loss from respiration is an indication of grain quality. They also stated that rough rice stored at 15 % and 18 % w. b. moisture con‐ tent fell below U. S. Grade Nos. 1 and 2 if DML exceed 0.75 %. Some authors assumed that an acceptable level of dry matter loss is 0.5 %. In high moisture maize (corn, 25 % m.c.) a loss of 0.5 % dry matter can occur in 7 days, sometime without any visible moulding. However, this way found to be sufficient to render maize grain unfit for use, and also to produce afla‐ toxins (Marin et al., 1999). Kreyger (1972) considered grain to be fit for animal feed with DML of up to <2 %. However, Hall and Dean (1978) suggested 1 % DML was acceptable in grain for food use and that this could be applied to both wheat and maize. White et al. (1982) stated that 0.1 % was unacceptable for wheat of premium grade and proposed the ab‐ solute limit of DML at 0.04 %. Therefore the problem of what is the limit for an acceptable level of dry matter loss is still controversial.

Seib et al. (1980) developed the following expression to determine DML of long-grain rough rice as a function of grain temperature, grain moisture content, and storage time:

$$\text{DML} = 1 - \exp\left(-At^{\text{C}} \exp\left[\mathcal{D}\left(1.8T - 28\right)\right] \text{exp}\left[E\left(M\_w - 0.14\right)\right]\right) \tag{5}$$

where DML is the dry matter loss in decimal form, *t* is the storage time in h 10-3, *T* is the grain temperature in °C, *Mw* is the grain moisture content in decimal w. b., and *A*, *C*, *D*, and *E* are empirical constants.

Equation (5) was developed for rice with constant airflow being forced through the grain and for the average grain temperature and the average grain moisture content over the stor‐ age time in question. The aerobic conditions were moreover assumed. When rice is stored in airtight units a shortage of O2 would decrease the respiration rate as well as decrease the rate of DML. Therefore, for bunker conditions, equation (5) would be expected to overesti‐ mate the actual DML since it was based on the premise of having adequate O2 to be used by the respiration process (Freer et al., 1990; Hu et al., 2003).

Weinberg et al. (2008) examined the effect of various moisture contents on the quality of maize (corn) grains in self-regulated modified atmospheres during hermetic storage. The ex‐ periments were conducted *in vitro*. Maize at 14, 16, 18, 20 and 22 % m.c. was initially condi‐ tioned for 28 days in tightly wrapped plastic bags and then stored in sealed containers at 30°C for up to 75 days. Carbon dioxide produced within the containers replaced the oxygen. As the moisture content increased the time for O2 depletion shortened, from 600 h at 14 % m.c. to 12 h at 22 %. The maize at 20 and 22 % m.c. exhibited the highest DML (0.59 % and 0.74 % respectively after 75 days) and the maize at 14 and 16 % m.c. the lowest (0.02 % and 0.15 %). Adhikarinayake et al. (2006) found out that during airtight storage of 14 % m.c. pad‐ dy in a ferro-cement bin, oxygen concentration dropped to 2.7 % within 30 days and carbon dioxide rose to 9.1 %. After 6 months storage, DML was 0.4 %. Varnova et al. (1995) noted that a sealed bulk of barley declined to 4 % O2 after 50 days.

When grain temperature and moisture content cannot be assumed constant for the entire storage time used, the method of rates was used to calculate DML (Freer et al., 1990):

$$\text{d(DML)} \Big/ \text{d}t = ACt^{\text{(C-1)}} \text{e}^y \text{e}^z \text{e}^{-\text{xe}^y \text{e}^z} \tag{6}$$

where *x=AtC*, *y*=*D*(1.8 *T*-28), *z*=*E*(*Mw*-0.14)

The values of the constants for long-grain rough rice used in the equations (5) and (6) were found to be (Seib et al., 1980): *A*=0.001889, *C*=0.7101, *D*=0.02740, *E*=31.63.

Thompson (1972) took into account negative influence of mechanical damages on dry matter loss and obtained the following expression to determine the DML (in %) of shelled corn:

$$\text{DML} = 0.0883 \left( \exp 0.006 t\_r - 1 \right) + 0.00102 t\_r \tag{7}$$

where:

where*X* is the rate of CO2 production in mg d-1 kg-1d. m., *t* is the storage time in d, and *Mw* is

There are however some problems in using equations (2) - (4) to describe quality changes. They are based on the measurement of CO2 release rate, either from a grain sample or direct‐ ly in a grain bin. Such measurements can be done using sophisticated equipment and in lab‐ oratory conditions. Additionally, when grain moisture is below 14 % (w. b.) the release rate is very low and therefore it is very difficult to measure it. However, the above formulas are

Another option for the prediction of safe storage life is the calculation of dry matter loss

Seib et al. (1980) stated that the amount of dry matter loss from respiration is an indication of grain quality. They also stated that rough rice stored at 15 % and 18 % w. b. moisture con‐ tent fell below U. S. Grade Nos. 1 and 2 if DML exceed 0.75 %. Some authors assumed that an acceptable level of dry matter loss is 0.5 %. In high moisture maize (corn, 25 % m.c.) a loss of 0.5 % dry matter can occur in 7 days, sometime without any visible moulding. However, this way found to be sufficient to render maize grain unfit for use, and also to produce afla‐ toxins (Marin et al., 1999). Kreyger (1972) considered grain to be fit for animal feed with DML of up to <2 %. However, Hall and Dean (1978) suggested 1 % DML was acceptable in grain for food use and that this could be applied to both wheat and maize. White et al. (1982) stated that 0.1 % was unacceptable for wheat of premium grade and proposed the ab‐ solute limit of DML at 0.04 %. Therefore the problem of what is the limit for an acceptable

Seib et al. (1980) developed the following expression to determine DML of long-grain rough

where DML is the dry matter loss in decimal form, *t* is the storage time in h 10-3, *T* is the grain temperature in °C, *Mw* is the grain moisture content in decimal w. b., and *A*, *C*, *D*, and

Equation (5) was developed for rice with constant airflow being forced through the grain and for the average grain temperature and the average grain moisture content over the stor‐ age time in question. The aerobic conditions were moreover assumed. When rice is stored in airtight units a shortage of O2 would decrease the respiration rate as well as decrease the rate of DML. Therefore, for bunker conditions, equation (5) would be expected to overesti‐ mate the actual DML since it was based on the premise of having adequate O2 to be used by

Weinberg et al. (2008) examined the effect of various moisture contents on the quality of maize (corn) grains in self-regulated modified atmospheres during hermetic storage. The ex‐

ë ûë û - - *E M* (5)

rice as a function of grain temperature, grain moisture content, and storage time:

DML 1 exp exp 1.8 28 exp 0.14 { ( ) ( ) } *<sup>C</sup> At D T <sup>w</sup>* =- - é ùé ù

(DML) as a function of grain temperature, grain moisture content, and storage time.

the moisture content in % w. b.

298 Advances in Agrophysical Research

not useful in prediction the storage life.

level of dry matter loss is still controversial.

the respiration process (Freer et al., 1990; Hu et al., 2003).

*E* are empirical constants.

$$t\_r = \frac{t}{M\_M \cdot M\_T \cdot M\_D} \tag{8}$$

$$M\_M = 0.103 \left[ \exp \left[ 455 \{ 100M \} ^{-1.53} \right] - 0.845M + 1.558 \right] \text{ for } 0.149 \le M \le 0.538 \,\text{kg} \text{ H}\_2\text{O-kg}^{-1} \text{d.m.} \tag{9}$$

$$M\_T = 32.3 \exp\left[-3.48(0.03T + 0.53)\right] \text{ for } T \le 15.6 \, \text{°C or } M\_w \le 19\% \tag{10}$$

$$M\_T = 32.3 \exp\left[-3.48\left(0.03T + 0.53\right)\right] + 0.01\left(M\_w - 19\right) \exp\left[0.61\left(0.03T - 0.47\right)\right] \tag{11}$$

for T>15.6°C and 19<*Mw*≤28%

$$M\_T = 32.3 \exp\left[-3.48\left(0.03T + 0.53\right)\right] + 0.09 \exp\left[0.61\left(0.03T - 0.47\right)\right] \tag{12}$$

where *t* is the storage time in d, *T* is the grain temperature in °C, *Mw* is the grain moisture

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Al-Yahya (2001) examined the conditions of safe storage of wheat. Based on these data the following relationship between storage time, grain temperature, grain moisture content and

( ( )) ( ) <sup>2</sup> exp 6.490336 0.024165 0.163337 1.292568 DML 0.9393 *<sup>w</sup> <sup>t</sup>* = -- + *T M <sup>R</sup>* <sup>=</sup> (16)

where *t* is the storage time in d, *T* is the grain temperature in °C, *Mw* is the grain moisture content in % w. b., DML is the dry matter loss in %, and 4°C≤*T*≤40°C, 15 % w. b. ≤*Mw*≤24 %

From Brooker et al. (1974) data and from Al-Yahya's (2001) data increase in the safe storage time of grains with the decrease of both grain temperature and moisture content can be ob‐

According to equation (1) heat energy is released during the respiratory process of grain, microorganisms and insects. The heat produced within the pockets of wet grain is especially harmful. It is not dissipated rapidly because of the low thermal conductivity of the grain (Kaleta, 1999; Kaleta and Górnicki, 2011) and the slow free convection currents in the granu‐ lar bulk. The elevated grain temperature and moisture content of the pocked provide a fa‐ vourable environment for further growth of microorganisms, thereby making the heating process self-accelerating. Heat production in stored grain ecosystems was investigated by e. g. Cofie-Agblor et al. (1997), Karunakaran et al. (2001), Scherer et al. (1980), and Zhang et al. (1992). Wilson (1999) proposed a mathematical model for predicting mould growth and sub‐ sequent heat generation in bulk stored grain. Unlike previous models, it was intended to be applicable in conditions that change with time. Starting from a model for mould growth in varying conditions the work of a number of authors was combined to produce a model to predict the heat production at all parts in a grain bulk. The effect of temperature and relative humidity on the mould growth rate was decoupled, so that the resulting equation for mould growth was a product of one-parameter terms. The heat generation rate was then written as a specific function of the mould population and mould grow rate. The model's current pre‐

dictions for very wet grains was good, but for dried grain model performs less well.

Spoilage of grains is the result of microorganisms (bacteria, yeast, fungi, and moulds) utiliz‐ ing the nutrients present in the grain for growth and reproductive processes, spoilage may result in a loss of nutrients from the grain since microorganisms use these nutrients in much the same way as livestock. Also, microorganisms produce heat and moisture during growth which can cause a temperature rise in stored grain. Heating initiated by microbial growth

content in % w. b., and 1°C≤*T*≤24°C, 15 %w. b. ≤*Mw*≤30 % w. b.

served. In such conditions the respiration of grains is less intensive.

DML can be presented:

w. b., 0.25 %≤DML≤1 %.

**3. Appearance of visible moulds**

for *T*>15.6°C and *Mw*>28%

$$M\_D = 0.001 \text{(MD)}^2 - 0.1101 \text{(MD)} + 3.426 \text{ for } 2 \text{ \%} \le \text{MD} \le 40 \text{ \%} \tag{13}$$

(equation (13) is developed by authors of the chapter on the basis of Steele et al. (1969) data)

where *T* is the grain temperature in °C, *Mw* is the grain moisture content in % w. b., *t* is the storage time in h, *MM* is the moisture multiplier, *MT* is the temperature multiplier, *MD* is the mechanical damage multiplier, and MD is the mechanical damage in %.

Scherer et al. (1980) investigated the dry matter loss of corn. Based on their data we devel‐ oped the following relationship between monthly DML, grain temperature and grain mois‐ ture content:

$$\text{DML} = 6.479 - 0.339T - 0.498M\_w + 0.002T^2 + 0.015TM\_w + 0.009M\_w^2 \left(R^2 = 0.9530\right) \tag{14}$$

where DML is the monthly dry matter loss in %, *T* is the grain temperature in °C, *Mw* is the grain moisture content in % w. b., and 5°C≤*T*≤20°C, 14 %w. b. ≤*Mw*≤35 % w. b.

From equation (5) and from Scherer (1980) data increase in the dry matter loss with the in‐ crease of both grain temperature and moisture content can be observed. In such conditions the respiration of grains is more intensive. DML increase with the duration of the grain stor‐ age.

Scherer's et al. (1980) investigations on damaged grain confirmed the negative influence of mechanical damages on dry matter loss shown by Thompson (1972). Scherer et al. (1980) stated that increase in amount of damaged corn caused the decrease in safe storage time. They accepted the limit of DML at 0.5 % and observed that 1 % of damaged grain together with 1 % of chaff and fines reduced the safe storage time in almost 6 %, however 20 % of damaged grain and 5 % of chaff and fines reduced the time in almost 38 %. They explained obtained results by more intensive respiration of chaff and fines, and damaged grain com‐ paring with undamaged grain.

Brooker et al. (1974) assumed for stored corn the limit of DML at 1 %. Based on their data the following relationship between safe storage time, grain temperature and grain moisture content can be presented:

$$\text{At } t = 3774.98 - 88.12T - 252.55M\_w + 0.587T^2 + 2.686T M\_w + 4.223M\_w^2 \left(R^2 = 0.861\right) \tag{15}$$

where *t* is the storage time in d, *T* is the grain temperature in °C, *Mw* is the grain moisture content in % w. b., and 1°C≤*T*≤24°C, 15 %w. b. ≤*Mw*≤30 % w. b.

Al-Yahya (2001) examined the conditions of safe storage of wheat. Based on these data the following relationship between storage time, grain temperature, grain moisture content and DML can be presented:

$$t = \exp\left(6.490336 - 0.024165T - 0.163337M\_w + 1.292568\,\text{(DML)}\right)\left(R^2 = 0.9393\right) \tag{16}$$

where *t* is the storage time in d, *T* is the grain temperature in °C, *Mw* is the grain moisture content in % w. b., DML is the dry matter loss in %, and 4°C≤*T*≤40°C, 15 % w. b. ≤*Mw*≤24 % w. b., 0.25 %≤DML≤1 %.

From Brooker et al. (1974) data and from Al-Yahya's (2001) data increase in the safe storage time of grains with the decrease of both grain temperature and moisture content can be ob‐ served. In such conditions the respiration of grains is less intensive.

According to equation (1) heat energy is released during the respiratory process of grain, microorganisms and insects. The heat produced within the pockets of wet grain is especially harmful. It is not dissipated rapidly because of the low thermal conductivity of the grain (Kaleta, 1999; Kaleta and Górnicki, 2011) and the slow free convection currents in the granu‐ lar bulk. The elevated grain temperature and moisture content of the pocked provide a fa‐ vourable environment for further growth of microorganisms, thereby making the heating process self-accelerating. Heat production in stored grain ecosystems was investigated by e. g. Cofie-Agblor et al. (1997), Karunakaran et al. (2001), Scherer et al. (1980), and Zhang et al. (1992). Wilson (1999) proposed a mathematical model for predicting mould growth and sub‐ sequent heat generation in bulk stored grain. Unlike previous models, it was intended to be applicable in conditions that change with time. Starting from a model for mould growth in varying conditions the work of a number of authors was combined to produce a model to predict the heat production at all parts in a grain bulk. The effect of temperature and relative humidity on the mould growth rate was decoupled, so that the resulting equation for mould growth was a product of one-parameter terms. The heat generation rate was then written as a specific function of the mould population and mould grow rate. The model's current pre‐ dictions for very wet grains was good, but for dried grain model performs less well.

## **3. Appearance of visible moulds**

32.3exp 3.48 0.03 0.53 0.09exp 0.61 0.03 0.47 ( ) ( ) *MT T <sup>T</sup>* = -é ù é ù ë û + - <sup>ë</sup> <sup>+</sup> <sup>û</sup> (12)

( ) ( ) <sup>2</sup> *MD* = - + ££ 0.001 MD 0.1101 MD 3.426 for 2 % MD 40 % (13)

(equation (13) is developed by authors of the chapter on the basis of Steele et al. (1969) data)

where *T* is the grain temperature in °C, *Mw* is the grain moisture content in % w. b., *t* is the storage time in h, *MM* is the moisture multiplier, *MT* is the temperature multiplier, *MD* is the

Scherer et al. (1980) investigated the dry matter loss of corn. Based on their data we devel‐ oped the following relationship between monthly DML, grain temperature and grain mois‐

( ) <sup>2</sup> 2 2 DML 6.479 0.339 0.498 0.002 0.015 0.009 0.9530 *<sup>w</sup> w w* =- - + + + = *T M T TM M R* (14)

where DML is the monthly dry matter loss in %, *T* is the grain temperature in °C, *Mw* is the

From equation (5) and from Scherer (1980) data increase in the dry matter loss with the in‐ crease of both grain temperature and moisture content can be observed. In such conditions the respiration of grains is more intensive. DML increase with the duration of the grain stor‐

Scherer's et al. (1980) investigations on damaged grain confirmed the negative influence of mechanical damages on dry matter loss shown by Thompson (1972). Scherer et al. (1980) stated that increase in amount of damaged corn caused the decrease in safe storage time. They accepted the limit of DML at 0.5 % and observed that 1 % of damaged grain together with 1 % of chaff and fines reduced the safe storage time in almost 6 %, however 20 % of damaged grain and 5 % of chaff and fines reduced the time in almost 38 %. They explained obtained results by more intensive respiration of chaff and fines, and damaged grain com‐

Brooker et al. (1974) assumed for stored corn the limit of DML at 1 %. Based on their data the following relationship between safe storage time, grain temperature and grain moisture

( ) <sup>2</sup> 2 2 3774.98 88.12 252.55 0.587 2.686 4.223 0.861 *<sup>w</sup> w w <sup>t</sup>* = -- + + + = *T M T TM M R* (15)

grain moisture content in % w. b., and 5°C≤*T*≤20°C, 14 %w. b. ≤*Mw*≤35 % w. b.

mechanical damage multiplier, and MD is the mechanical damage in %.

for *T*>15.6°C and *Mw*>28%

300 Advances in Agrophysical Research

ture content:

age.

paring with undamaged grain.

content can be presented:

Spoilage of grains is the result of microorganisms (bacteria, yeast, fungi, and moulds) utiliz‐ ing the nutrients present in the grain for growth and reproductive processes, spoilage may result in a loss of nutrients from the grain since microorganisms use these nutrients in much the same way as livestock. Also, microorganisms produce heat and moisture during growth which can cause a temperature rise in stored grain. Heating initiated by microbial growth can cause "heat damage" and can sometimes render grain unfit for feed. Such conditions have been known to cause fires and dust explosions in storage structures (Ross et al., 1979).

species of seed – borne fungi. Fungal spores and mycelia contain small amounts of essential nutrients (e. g. vitamins of the B complex and steroids), and moisture levels adequate for the metabolic demands of mites. The constant migration of mite populations within a granary ecosystem efficiently contributes to the dispersal of viable fungal spores of several species, including *Aspergillus* spp. and *Penicillium* spp., carried on the vector's body surface or de‐

Criteria of Determination of Safe Grain Storage Time – A Review

http://dx.doi.org/10.5772/52235

303

Conditions favouring the development of mycotoxins in cereals before and after harvest are important to grain – exporting countries concerned with marketing high – quality products. In post-harvest situation, crop spoilage, fungal growth, and mycotoxin formulation result from the interaction of several factors in the storage environment. These factors include: moisture, temperature, time, insect vectors, damage to the seed, oxygen levels, composition of substrate, fungal infection level, prevalence of toxigenic strains of fungi, and microbiolog‐ ical interactions. An understanding of the interactions involved would facilitate prediction

Investigations of conditions favouring the development of mycotoxins in grains before and after harvest were carried out by many researches for the following grains: barley (Abram‐ son et al., 1999; Gawrysiak-Witulska et al., 2008), canola (Pronyk et al., 2006), maize (corn) (Franzolin et al., 1999; Liu et al., 2006; Marin et al., 1999; Orsi et al., 2000; Reed et al., 2007; Wicklow et al., 1998), rice (Liu et al., 2006; Abdullah et al., 2000), wheat (Abramson et al.,

Abramson et al. (1999) stated that ochratoxin A, citrinin and sterigmatocystin reached mean levels of 24.38 and 411 ppb by 20 weeks in the 19 % moisture content barley, but were absent in the 15 % m.c. barley, and no other mycotoxins were detected. *Penicillium* species and *As‐ pergillusversicolor* (Vuill.) Tiraboschi comprised the predominant microflora. The effect of storage time was apparent at both 15 and 19 % moisture content for grain temperature, *Al‐ ternaria alternata* (Fr.) Keissler, *Penicillium* species and *Aspergillus versicolor*. At 19 % moisture content, storage time also affected moisture content, CO2 level, ergosterol content, seed ger‐ mination, and mycotoxin production. At 19 % m.c., elevated ergosterol levels at weeks 4 and 8 appears to offer early warning of the appearance of sterigmatocystin at week 12, and of

Pronyk et al. (2006) found that total ergosterol (fungal – specific membrane lipid used as an indicator of fungal infection in grain) levels in stored canola increased with storage time,

Liu et al. (2006) noted that no significant linear relationship existed in whole grain rice and brown rice between the amount of aflatoxins and the length of storage. The amount of afla‐ toxins in whole grain rice samples from 1 to 10 yr ranged from 2.79 to 2.93 μg kg-1 and peaked in the samples that were storage for 7-8 yr (6.23 μg kg-1). With increasing storage length, the aflatoxin content in brown rice was consistently low ranging from 0.74 to 1.19 μg kg-1. However, in maize samples, the amount of aflatoxins significantly increased with stor‐ age length. The average amount of aflatoxins in 1-yr maize was only 0.84 μg kg-1, while in 2-

and prevention of mycotoxin development in grains (Abramson et al., 2005).

posited with its feces (Franzolin et al., 1999).

2005; Padin et al., 2002).

ochratoxin A and citrinin at week 20.

temperature, and seed moisture content.

Certain microorganisms, when allowed to grow under the proper environmental conditions, can produce toxins or other products which, if consumed by either livestock or humans, can cause serious illness and even death. A number of these toxins and the microorganisms which produce them have been identified.

Toxigenic fungi infect agricultural crops both in the field and in storage. Converse et al. (1973) found the following variety of fungi in the corn at harvest and after 28 days of aera‐ tion in bins: *Fusarium*, *Cephalosporium*, *Alternaria*, *Cladosporium*, *Mucor*, *Nigrospora*, *Penicilli‐ um*, *Aspergillus flavus, A. glaucus*, *A. niger*, and *A. ochraceus*. Pronyk et al. (2006) noted that initial fungal counts showed that canola seeds were infected with high levels of pre-harvest fungi *Alternaria alternata*(Fr.) Keissl. and *Cladosporium* spp. and low levels of storage fungi *Eurotium* spp., *Aspergillus candidus* Link, and *Penicillium* spp.

Fungal infections can be discolour grain, change its chemical and nutritional characteristics, reduce germination and, most importantly, contaminate it with mycotoxins, the poisonous metabolites produced by certain fungal genera.

Ergot is a disease of cereal crops caused by the fungus *Claviceps purpurea*. It causes reduced yield and quality of grain. The effect of the ergot's alkaloid toxins on man and animals is, however, of much greater significance (Moreda and Ruiz-Altisent, 2011).

Aflatoxins are secondary metabolites produced by *Aspergillus flavus* Link and *A. parasiticus* Speare. These compounds are only few of over 120 mycotoxins produced by fungi. The afla‐ toxin's dietary effect upon poultry can result in poor growth, increased mortality, poor feed conversion, and increased condemnations. A number of other animal species are also subject to alfatoxicosis. Aflatoxin has been know to act as a potent toxin, a carcinogen, a teratogen, and a mutagen (Brekke et al., 1977; Liu et al., 2006; Wieman et al., 1986).

The fumonisins are secondary metabolites produced by *Fusariummonili forme* Sheldon and *F. proliferatum* (Matsushima) Niremberg. They show a worldwide distribution and can be iso‐ lated from maize and maize-based food and foodstuffs naturally contamined with *Fusarium*. The fumonisins have been associated with leukoencephalomalacia (ELEM) in equines, por‐ cine pulmonary edema (PPE), diarrhea and reduced body weight in broiler chicks, carcino‐ genicity in rats and leukoencephalomalacia and hemorrhage in the brain of rabbits. In addition, epidemiological evidence suggest a correlation between the consumption of *F. moniliforme* contaminated maize and a high incidence of human esophageal carcinoma (Mar‐ in et al., 1999; Orsi et al., 2000).

Mites also infect stored cereals. These arthropods contaminate grains and are a matter of great concern in the medical and veterinary fields, since they may act as carriers of bacteria and toxigenic fungi. Grains contaminated by mites may cause acute enteritis when ingested, and severe dermatitis and allergy in cereal handlers. Furthermore, mites can feed on the germ of kernels, thereby reducing the content of iron and vitamins of the B complex and germination ability. Stored – product mites can survive and multiply by feeding on several species of seed – borne fungi. Fungal spores and mycelia contain small amounts of essential nutrients (e. g. vitamins of the B complex and steroids), and moisture levels adequate for the metabolic demands of mites. The constant migration of mite populations within a granary ecosystem efficiently contributes to the dispersal of viable fungal spores of several species, including *Aspergillus* spp. and *Penicillium* spp., carried on the vector's body surface or de‐ posited with its feces (Franzolin et al., 1999).

can cause "heat damage" and can sometimes render grain unfit for feed. Such conditions have been known to cause fires and dust explosions in storage structures (Ross et al., 1979).

Certain microorganisms, when allowed to grow under the proper environmental conditions, can produce toxins or other products which, if consumed by either livestock or humans, can cause serious illness and even death. A number of these toxins and the microorganisms

Toxigenic fungi infect agricultural crops both in the field and in storage. Converse et al. (1973) found the following variety of fungi in the corn at harvest and after 28 days of aera‐ tion in bins: *Fusarium*, *Cephalosporium*, *Alternaria*, *Cladosporium*, *Mucor*, *Nigrospora*, *Penicilli‐ um*, *Aspergillus flavus, A. glaucus*, *A. niger*, and *A. ochraceus*. Pronyk et al. (2006) noted that initial fungal counts showed that canola seeds were infected with high levels of pre-harvest fungi *Alternaria alternata*(Fr.) Keissl. and *Cladosporium* spp. and low levels of storage fungi

Fungal infections can be discolour grain, change its chemical and nutritional characteristics, reduce germination and, most importantly, contaminate it with mycotoxins, the poisonous

Ergot is a disease of cereal crops caused by the fungus *Claviceps purpurea*. It causes reduced yield and quality of grain. The effect of the ergot's alkaloid toxins on man and animals is,

Aflatoxins are secondary metabolites produced by *Aspergillus flavus* Link and *A. parasiticus* Speare. These compounds are only few of over 120 mycotoxins produced by fungi. The afla‐ toxin's dietary effect upon poultry can result in poor growth, increased mortality, poor feed conversion, and increased condemnations. A number of other animal species are also subject to alfatoxicosis. Aflatoxin has been know to act as a potent toxin, a carcinogen, a teratogen,

The fumonisins are secondary metabolites produced by *Fusariummonili forme* Sheldon and *F. proliferatum* (Matsushima) Niremberg. They show a worldwide distribution and can be iso‐ lated from maize and maize-based food and foodstuffs naturally contamined with *Fusarium*. The fumonisins have been associated with leukoencephalomalacia (ELEM) in equines, por‐ cine pulmonary edema (PPE), diarrhea and reduced body weight in broiler chicks, carcino‐ genicity in rats and leukoencephalomalacia and hemorrhage in the brain of rabbits. In addition, epidemiological evidence suggest a correlation between the consumption of *F. moniliforme* contaminated maize and a high incidence of human esophageal carcinoma (Mar‐

Mites also infect stored cereals. These arthropods contaminate grains and are a matter of great concern in the medical and veterinary fields, since they may act as carriers of bacteria and toxigenic fungi. Grains contaminated by mites may cause acute enteritis when ingested, and severe dermatitis and allergy in cereal handlers. Furthermore, mites can feed on the germ of kernels, thereby reducing the content of iron and vitamins of the B complex and germination ability. Stored – product mites can survive and multiply by feeding on several

which produce them have been identified.

302 Advances in Agrophysical Research

*Eurotium* spp., *Aspergillus candidus* Link, and *Penicillium* spp.

however, of much greater significance (Moreda and Ruiz-Altisent, 2011).

and a mutagen (Brekke et al., 1977; Liu et al., 2006; Wieman et al., 1986).

metabolites produced by certain fungal genera.

in et al., 1999; Orsi et al., 2000).

Conditions favouring the development of mycotoxins in cereals before and after harvest are important to grain – exporting countries concerned with marketing high – quality products. In post-harvest situation, crop spoilage, fungal growth, and mycotoxin formulation result from the interaction of several factors in the storage environment. These factors include: moisture, temperature, time, insect vectors, damage to the seed, oxygen levels, composition of substrate, fungal infection level, prevalence of toxigenic strains of fungi, and microbiolog‐ ical interactions. An understanding of the interactions involved would facilitate prediction and prevention of mycotoxin development in grains (Abramson et al., 2005).

Investigations of conditions favouring the development of mycotoxins in grains before and after harvest were carried out by many researches for the following grains: barley (Abram‐ son et al., 1999; Gawrysiak-Witulska et al., 2008), canola (Pronyk et al., 2006), maize (corn) (Franzolin et al., 1999; Liu et al., 2006; Marin et al., 1999; Orsi et al., 2000; Reed et al., 2007; Wicklow et al., 1998), rice (Liu et al., 2006; Abdullah et al., 2000), wheat (Abramson et al., 2005; Padin et al., 2002).

Abramson et al. (1999) stated that ochratoxin A, citrinin and sterigmatocystin reached mean levels of 24.38 and 411 ppb by 20 weeks in the 19 % moisture content barley, but were absent in the 15 % m.c. barley, and no other mycotoxins were detected. *Penicillium* species and *As‐ pergillusversicolor* (Vuill.) Tiraboschi comprised the predominant microflora. The effect of storage time was apparent at both 15 and 19 % moisture content for grain temperature, *Al‐ ternaria alternata* (Fr.) Keissler, *Penicillium* species and *Aspergillus versicolor*. At 19 % moisture content, storage time also affected moisture content, CO2 level, ergosterol content, seed ger‐ mination, and mycotoxin production. At 19 % m.c., elevated ergosterol levels at weeks 4 and 8 appears to offer early warning of the appearance of sterigmatocystin at week 12, and of ochratoxin A and citrinin at week 20.

Pronyk et al. (2006) found that total ergosterol (fungal – specific membrane lipid used as an indicator of fungal infection in grain) levels in stored canola increased with storage time, temperature, and seed moisture content.

Liu et al. (2006) noted that no significant linear relationship existed in whole grain rice and brown rice between the amount of aflatoxins and the length of storage. The amount of afla‐ toxins in whole grain rice samples from 1 to 10 yr ranged from 2.79 to 2.93 μg kg-1 and peaked in the samples that were storage for 7-8 yr (6.23 μg kg-1). With increasing storage length, the aflatoxin content in brown rice was consistently low ranging from 0.74 to 1.19 μg kg-1. However, in maize samples, the amount of aflatoxins significantly increased with stor‐ age length. The average amount of aflatoxins in 1-yr maize was only 0.84 μg kg-1, while in 2yr maize it was as high as 1.17 μg kg-1. Practically, no maize grains were kept in storage for more than 3 yr.

**Grain Coefficients** *R2* **Range of application**

Criteria of Determination of Safe Grain Storage Time – A Review

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305

wheat 50.66928 -0.272909 -2.52755 0.9707 16.1 %w.b.≤*Mw*≤23.0 %w.b. barley 27.04320 -0.174362 -1.17856 0.9727 15.6. %w.b.≤*Mw*≤22.7 %w.b. oats 31.60300 -0.201594 -1.55997 0.9728 14.8 %w.b.≤*Mw*≤22.0 %w.b. rye 34.58371 -0.283607 -1.58288 0.9779 15.4 %w.b.≤*Mw*≤24.4 %w.b.

Equation (17) and (18) confirm that the duration of the safe storage time increases with the decrease of both grain temperature and grain moisture content. Such conditions are not fa‐

There are, however, controversies about the criterion of appearance of visible moulds. Sev‐ eral researches (Ryniecki and Nellist, 1991; Nellist, 1998), followed Kreyger (1972), took it as the best criterion for safe storage time. Some of them (Armitage, 1986; Fleurat-Lessard, 2002) mentioned, however, several drawbacks of this criterion. The main drawback of this kind of prediction of safe storage life of stored grain is the subjective determination of visible mould on the kernel. Another drawback is the lack of progressiveness in the prediction. Before the onset of visible spoilage, grain is theoretically sound and its quality is not altered. The day

Various factors can reduce the storage life of some premium grade quality cereals. Moisture content of the harvested grains and storage temperature can encourage mould and insect pest damage. The best studied quality parameter is germination capacity, which is only of direct importance for grains. Nevertheless, this is probably the best surrogate measure of ce‐ real grain soundness (Pomeranz, 1982). Cereals retaining a high level of viability in storage are also likely to retain the other main parameters of commercial or technological quality

Germination is defined as the appearance of the first signs of growth, i. e. the visible protru‐ sion of the radical (Black, 1970). Germination can be affected by many factors such as grain temperature, grain moisture content, grain damages, fungus and insect infection. Much re‐

McNeal (1966) found that soybean can be kept for 12 months without an expressive decline in germination if the temperature is kept below 16°C and the moisture content is not higher than 16.2 %, dry basis. Mayeux et al. (1972) noted than the germination of soybean seed is influenced by the percentage of split beans in stored seed, and storage temperature and moisture play an important role in maintaining the soybean seed quality. Kreyger (1972)

search has been conducted to determine the effect of various factors on germination.

after spoilage is seen, the grain is deteriorated and should be downgraded.

*A B C*

**Table 1.** Values of coefficients in equation (18) and range of application

vourable for the mould development.

**4. Germination capacity**

(Fleurat-Lessard, 2002).

Franzolin et al. (1999) examined the ability of mites of the species *Tyrophagus putrescentiae* to spread the toxigenic fungus *Aspergillus flavus* from contaminated maize to sterile grains un‐ der controlled conditions. The obtained results confirms that *T. putrescentiae* is a means of dispersal for toxigenic fungi in stored grain kept under warm and moist conditions. The lev‐ els of aflatoxin contamination recorded after 90 days of incubation exceeded the safe limits established by Brazilian legislation.

Abdullah et al. (2000) examined the average numbers of days before visible fungal develop‐ ment at 25°C on, among others, ordinary rice and glutinous rice. They found that ordinary rice at 13.0 % moisture content (d. b.) and glutinous rice at 12.9 % m.c. (d. b.) would be safe for about 2 months (57±2 days and 73±1 days respectively). However, ordinary rice at 14.1 % m.c. and glutinous rice at 14.2 % m.c. may spoil in about 20 days. Hence, an error in the moisture content of 1.1 % for rice and 1.3 % for glutinous rice is disastrous. At 21.9 % m.c. ordinary rice and 25.6 % m.c. glutinous rice the data indicated a shell-life of about 7 days.

Abramson et al. (2005) stated that ochratoxin A and citrinin reached mean levels of 6.5 and 11.6 mg kg-1, respectively, by 20 weeks at 20 % m.c., but were absent at 16 % m.c., and no other mycotoxins were found. *Penicillium* species were the predominant microflora. Ergo‐ sterol levels remained between 3.9 and 8.4 mg kg-1 at 16 % m.c., but increased from 3.9 to 55.5 mg kg-1 at 20 % m.c. during 20-week trial period.

There is, however, lack of simple equations predicting the length of safe storage period by a combination of, at least, moisture content of grain and storage temperature.

Bailey and Smith (1982) (cited after Bowden et al. (1983)) developed the following empirical formula predicting the duration of a safe barley storage period without occurrence of visible mould under the good aeration conditions:

$$t = 67 + \exp\left[5.124 + \left(39.6 - 0.8107T\right)\left[\left(M\_w - 12\right)^{-1} - 0.0315 \exp 0.0579T\right]\right] \tag{17}$$

where *t* is the storage time in h, *T* is the grain temperature in °C, *Mw* is the grain moisture content in % w. b., and 5°C≤*T*≤25°C, 16 % w. b. ≤ *Mw* ≤26 % w. b.

Kreyger (1972) investigated the safe storage times of several grains. He assumed that the best criterion for safe storage times is the one that is based on the time to the appearance of visible moulds. Based on Kreyger's (1972) data, we developed the following formula:

$$t = \exp\left(A + BT + CM\_w\right) \tag{18}$$

where *t* is the storage time in weeks, *T* is the grain temperature in °C, *Mw* is the grain mois‐ ture content in % w. b., *A*, *B*, *C* are empirical constants given in Table 1, and 10°C≤*T*≤25°C.


**Table 1.** Values of coefficients in equation (18) and range of application

Equation (17) and (18) confirm that the duration of the safe storage time increases with the decrease of both grain temperature and grain moisture content. Such conditions are not fa‐ vourable for the mould development.

There are, however, controversies about the criterion of appearance of visible moulds. Sev‐ eral researches (Ryniecki and Nellist, 1991; Nellist, 1998), followed Kreyger (1972), took it as the best criterion for safe storage time. Some of them (Armitage, 1986; Fleurat-Lessard, 2002) mentioned, however, several drawbacks of this criterion. The main drawback of this kind of prediction of safe storage life of stored grain is the subjective determination of visible mould on the kernel. Another drawback is the lack of progressiveness in the prediction. Before the onset of visible spoilage, grain is theoretically sound and its quality is not altered. The day after spoilage is seen, the grain is deteriorated and should be downgraded.

## **4. Germination capacity**

yr maize it was as high as 1.17 μg kg-1. Practically, no maize grains were kept in storage for

Franzolin et al. (1999) examined the ability of mites of the species *Tyrophagus putrescentiae* to spread the toxigenic fungus *Aspergillus flavus* from contaminated maize to sterile grains un‐ der controlled conditions. The obtained results confirms that *T. putrescentiae* is a means of dispersal for toxigenic fungi in stored grain kept under warm and moist conditions. The lev‐ els of aflatoxin contamination recorded after 90 days of incubation exceeded the safe limits

Abdullah et al. (2000) examined the average numbers of days before visible fungal develop‐ ment at 25°C on, among others, ordinary rice and glutinous rice. They found that ordinary rice at 13.0 % moisture content (d. b.) and glutinous rice at 12.9 % m.c. (d. b.) would be safe for about 2 months (57±2 days and 73±1 days respectively). However, ordinary rice at 14.1 % m.c. and glutinous rice at 14.2 % m.c. may spoil in about 20 days. Hence, an error in the moisture content of 1.1 % for rice and 1.3 % for glutinous rice is disastrous. At 21.9 % m.c. ordinary rice and 25.6 % m.c. glutinous rice the data indicated a shell-life of about 7 days.

Abramson et al. (2005) stated that ochratoxin A and citrinin reached mean levels of 6.5 and 11.6 mg kg-1, respectively, by 20 weeks at 20 % m.c., but were absent at 16 % m.c., and no other mycotoxins were found. *Penicillium* species were the predominant microflora. Ergo‐ sterol levels remained between 3.9 and 8.4 mg kg-1 at 16 % m.c., but increased from 3.9 to

There is, however, lack of simple equations predicting the length of safe storage period by a

Bailey and Smith (1982) (cited after Bowden et al. (1983)) developed the following empirical formula predicting the duration of a safe barley storage period without occurrence of visible

where *t* is the storage time in h, *T* is the grain temperature in °C, *Mw* is the grain moisture

Kreyger (1972) investigated the safe storage times of several grains. He assumed that the best criterion for safe storage times is the one that is based on the time to the appearance of

where *t* is the storage time in weeks, *T* is the grain temperature in °C, *Mw* is the grain mois‐ ture content in % w. b., *A*, *B*, *C* are empirical constants given in Table 1, and 10°C≤*T*≤25°C.

visible moulds. Based on Kreyger's (1972) data, we developed the following formula:

ê ú ë û (17)

xp( )e *<sup>w</sup> t A BT CM* = ++ (18)

{ ( ) ( ) } <sup>1</sup> 67 exp 5.124 39.6 0.8107 12 0.0315exp0.0579 *<sup>w</sup> <sup>t</sup> T M <sup>T</sup>* - =+ + - - - é ù

combination of, at least, moisture content of grain and storage temperature.

content in % w. b., and 5°C≤*T*≤25°C, 16 % w. b. ≤ *Mw* ≤26 % w. b.

more than 3 yr.

304 Advances in Agrophysical Research

established by Brazilian legislation.

55.5 mg kg-1 at 20 % m.c. during 20-week trial period.

mould under the good aeration conditions:

Various factors can reduce the storage life of some premium grade quality cereals. Moisture content of the harvested grains and storage temperature can encourage mould and insect pest damage. The best studied quality parameter is germination capacity, which is only of direct importance for grains. Nevertheless, this is probably the best surrogate measure of ce‐ real grain soundness (Pomeranz, 1982). Cereals retaining a high level of viability in storage are also likely to retain the other main parameters of commercial or technological quality (Fleurat-Lessard, 2002).

Germination is defined as the appearance of the first signs of growth, i. e. the visible protru‐ sion of the radical (Black, 1970). Germination can be affected by many factors such as grain temperature, grain moisture content, grain damages, fungus and insect infection. Much re‐ search has been conducted to determine the effect of various factors on germination.

McNeal (1966) found that soybean can be kept for 12 months without an expressive decline in germination if the temperature is kept below 16°C and the moisture content is not higher than 16.2 %, dry basis. Mayeux et al. (1972) noted than the germination of soybean seed is influenced by the percentage of split beans in stored seed, and storage temperature and moisture play an important role in maintaining the soybean seed quality. Kreyger (1972) used percentage germination as an indicator of grain deterioration. He studied the effect of many levels of grain moisture content and grain temperature on the percentage germina‐ tion. His findings will be discussed below.

mulated conditions, and determine the most advantageous conditions of conducting the

Muir and Sinha (1986) developed a set of two regression equations for predicting allowable

where *t* is the storage time in d, *Mw* is the grain moisture content in % w. b., *T* is the grain

Arinze et al. (1993) used equation (20) in their computer program developed to simulate inbin drying of canola grain, predict grain spoilage under the simulated conditions, and ob‐ tain an economic analysis of various drying schemes for canola for use as a management tool in the selection of the appropriate drying system. Equation (20) predicts the allowable storage times when canola is stored at constant temperatures and moisture contents. During a drying process, however, both temperature and moisture content vary with time. To pre‐ dict grain spoilage or deterioration under dynamic or changing conditions, Arinze et al. (1993) used spoilage index (SI). A value of *t* was computed at each interval Δ*t* from equation (20), and the calculated ratios of Δ*t*/*t* were calculated. Theoretically, grain loses 5 % of its germination when the sum of the computed Δ*t*/*t* values for each layer over the simulated

> 1 SI 1 *n*

*i i t t* <sup>=</sup>

where *n* is the number of simulated time steps. SI is a spoilage or storage index and its in‐ stantaneous value represents the progress of grain spoilage. A spoilage index of 1 or greater indicates that the allowable storage time has elapsed and the 5 % loss in germination has

Karunakaran et al. (2001) defined the safe storage time of wheat as the storage time for the germination to decrease to 90 % and developed the following correlation equation for 19 %

where *t* is the storage time in d, and *T* is the grain temperature in °C. They stated also, that the safe storage times of 17 % m.c. wheat were 5, 7, and 15 d at 35, 30, and 25°C, respec‐

=- - (20)

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307

æ ö <sup>D</sup> = = ç ÷ è ø <sup>å</sup> (21)

log 2.057 0.049 *t T* = - (22)

log 6.224 0.302 0.069 , for 11 % w.b. (a) log 5.278 0.206 0.063 , for ³11 % w.b. (b) *w w w w*

storage times for canola before the germination capacity drops by 5 %.

*t M TM t M TM* =- - <

process of wheat drying in silos.

temperature in °C, and 10°C≤*T*≤40°C.

drying period equals unity:

occurred to the canola.

tively.

m.c., wet basis, wheat at 10-35°C:

Parde et al. (2002) studied the storage behaviour of soybean seed and the loss in quality due to free-fall from different heights (0.5-2 m) on to different surfaces (cement and galvanized iron) were studied. They found that soybean seed is susceptible to mechanical damage. The severity of damage varies with moisture content of seed because the dryer seed is harder. The hight of fall produces significant effects on germination. An average germination loss of 10 % and 31 % was noticed when the seed fell from a height of 1 and 2 m, respectively, on to the cement floor. This drop in germination was 7.5 % and 22 % when dropped from the same heights on to galvanized floor. The seed lots held at 12 % moisture content, dry basis, suffered less damage during free-fall from different heights than the lots held at 10 % and 11 % m.c. Soybean seed lots at 12 % m.c. retained germination ability for a longer period than the seed lots at lower m.c.

Pronyk et al. (2006) stated that germination decreased with storage time, temperature, and moisture content. After 56 days, germination of canola stored at 12 % m.c., wet basis and at 25-30°C dropped till 73 %. The same value of germination stored: at 12 % m.c. and at 30-35°C showed after approximately 27 days, at 14 % m.c. and at 25-30°C showed after 29 days, at 14 % m.c. and at 30-35°C showed after 12 days.

Weinberg et al. (2008) examined the germination percentage of the maize (corn) stored in the self-regulated atmospheres in the sealed containers. They noticed that the germination per‐ centage decreased during the storage period, and decreased as the moisture content in‐ creased. With 18 % m.c. and above the germination percentage decreased to zero after 35 days of storage.

Genkawa et al. (2008) tested airtight storage of brown rice with a low moisture content. They stated that the germination rate of brown rice with 16.2 % m.c., wet basis, at 25°C de‐ clined from 97 % to 27 % but for rice with less than 12.8 % m.c. at 25°C germination was above 90 %.

There is, however, lack of simple equations predicting the length of safe storage period by combination of, at least, moisture content of grain and storage temperature.

Fraser and Muir (1981) developed a set of two regression equations for predicting allowable storage times for wheat before the germination capacity drops by 5 %:

$$\begin{aligned} \text{log } t &= 6.234 - 0.2118 \, M\_w - 0.0527T, \text{ for 12 \% w.b.} \le M\_w < 19 \,\% \le \text{w.b.} \quad \text{(a)}\\ \log t &= 4.129 - 0.0997M\_w - 0.0576T, \text{ for 19 \% w.b.} \le M\_w \le 24 \,\% \le \text{w.b.} \quad \text{(b)} \end{aligned} \tag{19}$$

where *t* is the storage time in d, *Mw* is the grain moisture content in % w. b., *T* is the grain temperature in °C, and 10°C≤*T*≤40°C.

Kaleta (1996) used equation (19) in her computer program developed to simulate wheat dry‐ ing in silos with radial (horizontal) and vertical airflow, predict grain spoilage under the si‐ mulated conditions, and determine the most advantageous conditions of conducting the process of wheat drying in silos.

used percentage germination as an indicator of grain deterioration. He studied the effect of many levels of grain moisture content and grain temperature on the percentage germina‐

Parde et al. (2002) studied the storage behaviour of soybean seed and the loss in quality due to free-fall from different heights (0.5-2 m) on to different surfaces (cement and galvanized iron) were studied. They found that soybean seed is susceptible to mechanical damage. The severity of damage varies with moisture content of seed because the dryer seed is harder. The hight of fall produces significant effects on germination. An average germination loss of 10 % and 31 % was noticed when the seed fell from a height of 1 and 2 m, respectively, on to the cement floor. This drop in germination was 7.5 % and 22 % when dropped from the same heights on to galvanized floor. The seed lots held at 12 % moisture content, dry basis, suffered less damage during free-fall from different heights than the lots held at 10 % and 11 % m.c. Soybean seed lots at 12 % m.c. retained germination ability for a longer period than

Pronyk et al. (2006) stated that germination decreased with storage time, temperature, and moisture content. After 56 days, germination of canola stored at 12 % m.c., wet basis and at 25-30°C dropped till 73 %. The same value of germination stored: at 12 % m.c. and at 30-35°C showed after approximately 27 days, at 14 % m.c. and at 25-30°C showed after 29

Weinberg et al. (2008) examined the germination percentage of the maize (corn) stored in the self-regulated atmospheres in the sealed containers. They noticed that the germination per‐ centage decreased during the storage period, and decreased as the moisture content in‐ creased. With 18 % m.c. and above the germination percentage decreased to zero after 35

Genkawa et al. (2008) tested airtight storage of brown rice with a low moisture content. They stated that the germination rate of brown rice with 16.2 % m.c., wet basis, at 25°C de‐ clined from 97 % to 27 % but for rice with less than 12.8 % m.c. at 25°C germination was

There is, however, lack of simple equations predicting the length of safe storage period by

Fraser and Muir (1981) developed a set of two regression equations for predicting allowable

where *t* is the storage time in d, *Mw* is the grain moisture content in % w. b., *T* is the grain

Kaleta (1996) used equation (19) in her computer program developed to simulate wheat dry‐ ing in silos with radial (horizontal) and vertical airflow, predict grain spoilage under the si‐

=- - £ £ (19)

log 6.234 0.2118 0.0527 , for 12 % w.b. 19 % w.b. (a) log 4.129 0.0997 0.0576 , for 19 % w.b. 24 % w.b. (b) *w w w w*

combination of, at least, moisture content of grain and storage temperature.

storage times for wheat before the germination capacity drops by 5 %:

*t MT M t MT M* =- - £ <

temperature in °C, and 10°C≤*T*≤40°C.

tion. His findings will be discussed below.

days, at 14 % m.c. and at 30-35°C showed after 12 days.

the seed lots at lower m.c.

306 Advances in Agrophysical Research

days of storage.

above 90 %.

Muir and Sinha (1986) developed a set of two regression equations for predicting allowable storage times for canola before the germination capacity drops by 5 %.

$$\begin{aligned} \log t &= 6.224 - 0.302 \, M\_w - 0.069T, \text{ for} \, M\_w < 11 \,\%\,\text{ w.b.} \,\text{(a)}\\ \log t &= 5.278 - 0.206 \, M\_w - 0.063T, \text{ for} \, M\_w \, ^311 \,\%\,\text{ w.b.} \,\text{ (b)} \end{aligned} \tag{20}$$

where *t* is the storage time in d, *Mw* is the grain moisture content in % w. b., *T* is the grain temperature in °C, and 10°C≤*T*≤40°C.

Arinze et al. (1993) used equation (20) in their computer program developed to simulate inbin drying of canola grain, predict grain spoilage under the simulated conditions, and ob‐ tain an economic analysis of various drying schemes for canola for use as a management tool in the selection of the appropriate drying system. Equation (20) predicts the allowable storage times when canola is stored at constant temperatures and moisture contents. During a drying process, however, both temperature and moisture content vary with time. To pre‐ dict grain spoilage or deterioration under dynamic or changing conditions, Arinze et al. (1993) used spoilage index (SI). A value of *t* was computed at each interval Δ*t* from equation (20), and the calculated ratios of Δ*t*/*t* were calculated. Theoretically, grain loses 5 % of its germination when the sum of the computed Δ*t*/*t* values for each layer over the simulated drying period equals unity:

$$\text{SI} = \sum\_{i=1}^{n} \left(\frac{\Delta t}{t}\right)\_i = 1 \tag{21}$$

where *n* is the number of simulated time steps. SI is a spoilage or storage index and its in‐ stantaneous value represents the progress of grain spoilage. A spoilage index of 1 or greater indicates that the allowable storage time has elapsed and the 5 % loss in germination has occurred to the canola.

Karunakaran et al. (2001) defined the safe storage time of wheat as the storage time for the germination to decrease to 90 % and developed the following correlation equation for 19 % m.c., wet basis, wheat at 10-35°C:

$$
\log t = 2.057 - 0.049T \tag{22}
$$

where *t* is the storage time in d, and *T* is the grain temperature in °C. They stated also, that the safe storage times of 17 % m.c. wheat were 5, 7, and 15 d at 35, 30, and 25°C, respec‐ tively.

The germination capacity of wheat at 17-19 % m.c., wet basis, stored at 25°C can be predict‐ ed from the measured respiration rate and moisture content by the equation (Karunakaran et al., 2001):

$$Y = 100 - 0.1X + 0.093M\_w \tag{23}$$

were *Y* is the germination capacity of grain in %, *Mw* is the grain moisture content in % w. b., MD is the mechanical damage in %, *A*, *B*, *C*, *D*, *E*, and *F* are empirical constants given in

Criteria of Determination of Safe Grain Storage Time – A Review

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309

**Grain Coefficients** *R2* **Range of application**

wheat 12.28039 -0.128973 -0.473026 0.9929 12.0 %w.b.≤*Mw*≤23.0 %w.b. barley 13.12305 -0.174000 -0.452103 0.9965 11.0. %w.b.≤*Mw*≤23.0 %w.b. oats 13.96125 -0.148378 -0.604968 0.9940 11.0 %w.b.≤*Mw*≤22.0 %w.b. rye 10.13185 -0.087999 -0.426973 0.9931 11.5 %w.b.≤*Mw*≤24.0 %w.b.

**T, °C DML, %** *A B C D E F R2*

4 0.5 -45.074 15.904 0.184 -0.475 -0.069 0.023 0.836703

15 0.5 -204.267 31.578 -0.412 -0.852 -0.024 0.008 0.928671

25 0.5 -37.747 13.559 -0.473 -0.381 -0.037 0.02 0.905906

40 0.5 -303.503 37.932 -2.536 -0.926 0.049 0.031 0.732198

0.25 -113.667 22.569 0.032 -0.594 -0.022 0.004 0.940542

1 246.235 -19.763 -0.074 0.507 -0.062 0.017 0.729865 0.25 -83.9483 19.1422 -1.207 -0.5037 -0.03733 0.048 0.72055

1 -80.551 15.347 -0.29 -0.42 -0.046 0.012 0.875763 0.25 -34.73 12.798 0.914 -0.323 -0.091 0.012 0.869765

1 207.167 -17.628 -0.06 0.481 -0.063 0.016 0.734423 0.25 -4.483 9.097 0.606 -0.214 -0.067 0.004 0.448631

1 5.479 -2.086 -1.064 0.207 -0.03 0.026 0.917996

( ) ( ) ( )

where *Y* is the germination capacity of grain in %, *T* is the grain temperature in °C, MD is the mechanical damage in %, *A*, *B*, *C*, *D*, *E*, and *F* are empirical constants given in Table 4,

<sup>2</sup> *Y A BT C DT ET F* =+ + + + + MD <sup>2</sup> MD MD (27)

Table 3, and 15 %w. b. ≤*Mw*≤24 %w. b., 0≤MD≤30 %.

*A B C*

**Table 2.** Values of coefficients in equation (25) and range of application

**Table 3.** Values of coefficients in equation (26)

and 4°C≤*T*≤40°C, 0≤MD≤30 %.

and the second one

where *Y* is the germination capacity of grain in %, *X* is the rate of CO2 production in mg d-1 kg-1d. m., and *Mw* is the grain moisture content in % w. b.

Equation (23) is useful to determine the condition of the grains coming to grain-handling fa‐ cilities, for which the storage conditions (time and temperature) are not known but the mois‐ ture content and respiration rate of the grain can be determined in 2 h rather than the 7 d required for germination. For wheat stored for a known length of time at 25°C and moisture levels of 17-19 %, the germination capacity can be predicted from the storage time, moisture content of the stored grain, and CO2 production (Karunakaran et al., 2001):

$$Y = 54.56 - 1.213t + 2.823M\_w - 0.076X \tag{24}$$

where *Y* is the germination capacity of grain in %, *t* is storage time in d, *Mw* is the grain moisture content in % w. b., and *X* is the rate of CO2 production in mg d-1 kg-1d. m.

Based on the germination data of Kreyger (1972), we developed the following formulas for predicting allowable storage times:

$$t = \exp\left(A + BT + \mathcal{C}M\_w\right) \tag{25}$$

were *t* is storage time in weeks, *T* is the grain temperature in °C, *Mw* is the grain moisture content in % w. b., *A*, *B*, *C* are empirical constants given in Table 2, and 10°C≤*T*≤20°C.

Al-Yahya (2001) explored some of the factors and conditions, such as grain moisture, grain temperature, and mechanical grain damage, that influence the germination of grain at vari‐ ous levels of dry matter loss during wheat storage. The objective was to determine the changes in percentage germination of stored wheat at different levels of DML under differ‐ ent storage conditions, i. e. different grain moisture contents, temperatures and levels of me‐ chanical damage (MD). Based on Al-Yahya's (2001) data, we developed the following formulas:

the first one

$$Y = A + BM\_w + C\left(\text{MD}\right) + DM\_w^{\;\;\;2} + EM\_w\left(\text{MD}\right) + F\left(\text{MD}\right)^2\tag{26}$$

were *Y* is the germination capacity of grain in %, *Mw* is the grain moisture content in % w. b., MD is the mechanical damage in %, *A*, *B*, *C*, *D*, *E*, and *F* are empirical constants given in Table 3, and 15 %w. b. ≤*Mw*≤24 %w. b., 0≤MD≤30 %.


**Table 2.** Values of coefficients in equation (25) and range of application


**Table 3.** Values of coefficients in equation (26)

and the second one

The germination capacity of wheat at 17-19 % m.c., wet basis, stored at 25°C can be predict‐ ed from the measured respiration rate and moisture content by the equation (Karunakaran

where *Y* is the germination capacity of grain in %, *X* is the rate of CO2 production in mg d-1

Equation (23) is useful to determine the condition of the grains coming to grain-handling fa‐ cilities, for which the storage conditions (time and temperature) are not known but the mois‐ ture content and respiration rate of the grain can be determined in 2 h rather than the 7 d required for germination. For wheat stored for a known length of time at 25°C and moisture levels of 17-19 %, the germination capacity can be predicted from the storage time, moisture

where *Y* is the germination capacity of grain in %, *t* is storage time in d, *Mw* is the grain

Based on the germination data of Kreyger (1972), we developed the following formulas for

were *t* is storage time in weeks, *T* is the grain temperature in °C, *Mw* is the grain moisture

Al-Yahya (2001) explored some of the factors and conditions, such as grain moisture, grain temperature, and mechanical grain damage, that influence the germination of grain at vari‐ ous levels of dry matter loss during wheat storage. The objective was to determine the changes in percentage germination of stored wheat at different levels of DML under differ‐ ent storage conditions, i. e. different grain moisture contents, temperatures and levels of me‐ chanical damage (MD). Based on Al-Yahya's (2001) data, we developed the following

( ) ( ) ( )

content in % w. b., *A*, *B*, *C* are empirical constants given in Table 2, and 10°C≤*T*≤20°C.

<sup>2</sup> *Y A BM C DM EM F* =+ + + + + *<sup>w</sup>* MD *w w*

moisture content in % w. b., and *X* is the rate of CO2 production in mg d-1 kg-1d. m.

content of the stored grain, and CO2 production (Karunakaran et al., 2001):

kg-1d. m., and *Mw* is the grain moisture content in % w. b.

predicting allowable storage times:

formulas:

the first one

100 0.1 0.093 *Y XMw* =- + (23)

54.56 1.213 2.823 0.076 *Y tM X <sup>w</sup>* =- + - (24)

*t A BT CM* = ++ exp( *<sup>w</sup>* ) (25)

<sup>2</sup> MD MD (26)

et al., 2001):

308 Advances in Agrophysical Research

$$Y = A + BT + C \left(\text{MD}\right) + DT^2 + ET \left(\text{MD}\right) + F \left(\text{MD}\right)^2\tag{27}$$

where *Y* is the germination capacity of grain in %, *T* is the grain temperature in °C, MD is the mechanical damage in %, *A*, *B*, *C*, *D*, *E*, and *F* are empirical constants given in Table 4, and 4°C≤*T*≤40°C, 0≤MD≤30 %.

Equations presented in this section confirm that the changes in germination capacity of stor‐ ed grain are lower with lower following parameters: grain temperature, grain moisture con‐ tent, mechanical damage and storage time. In general, the conclusions are the same as in previous section: longer storage times are possible with lower both grain moisture contents and temperatures and with lower levels of mechanical grain damages.

0

*<sup>A</sup> EA <sup>n</sup> k A t RT*

where *A* is amount of a quality factor, ±d*A*/d*t* is the rate loss of a quality factor or produc‐ tion of undesirable effects, *k*0 is the pre-exponential factor, *EA* is the activation energy in J mol-1, *R* is the gas constant in J mol-1 K-1, *T* is the temperature in K, and *n* is the reaction or‐

Somponronnarit et al. (1998) stated that the yellowing rate of paddy can be explained by temperature and water activity and developed the following empirical equations to predict

> d d *<sup>b</sup> <sup>k</sup> t*

( ) 25919.13 10712.78 RH ( ) ln 71.87 25.32 RH *<sup>k</sup>*

where *b* is yellowness of rice in Hunter *b* unit, *t* is the time in d, *k* is the constant value for the yellowing rate in Hunter *b* unit d-1, RH is the relative humidity in decimal, *T* is the tem‐

Courtois (1995) developed the following empirical equation to predict the change in the wet-

0

*<sup>A</sup> <sup>Q</sup> <sup>E</sup> k Q <sup>t</sup> RT*

exp <sup>d</sup>

d

*T T* =- - + (30)

2

<sup>0</sup> *k* =- + + 1.9561·10 5.4287·10 6.8210·10 *M M* (32)

16 17 17 2

where *Q* is the wet-milling quality, *t* is the time in s, *k*0 is the pre-exponential factor in s-1, *T* is the temperature in K, *M* is the grain moisture content in decimal d. b., and *R* is the gas con‐

æ ö =- -ç ÷ è ø (31)

æ ö ±= -ç ÷ è ø (28)

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311

= (29)

exp <sup>d</sup>

d

der (1 for first-order, 0 for zero-order).

perature in K, and 308 K≤*T*≤338 K, 0.80≤RH≤0.95.

milling quality of corn:

stant in J mol-1 K-1, *EA*=-133200 J mol-1.

the change in the yellow colour:

and

and

At the end of the chapter it is worth to mention shortly the other grain quality criteria which can be important to consumer and food manufacturer.

Colour of white rice is an important criterion for judging quality and price. The white colour becomes yellow after a period of storage. Dry matter loss of grain and heat liberated from its respiration and biological activities may accelerate rice yellowing. Parameters affecting the rice yellowing are temperature and relative humidity (water activity) (Soponronnarit et al., 1998; Tirawanichakul et al., 2004).


**Table 4.** Values of coefficients in equation (27)

Corn quality can mean wet-milling quality. It corresponds to the amount of survival ther‐ mo-sensitive proteins inside the grains and is very well correlated with the thermal history of the grains (Courtois, 1995).

The rate of quality changing can be represented with a simple zero- or first-order reaction (Labuza, 1980):

$$\pm \frac{\mathbf{d}A}{\mathbf{d}t} = k\_0 \exp\left(-\frac{E\_A}{RT}\right) A'' \tag{28}$$

where *A* is amount of a quality factor, ±d*A*/d*t* is the rate loss of a quality factor or produc‐ tion of undesirable effects, *k*0 is the pre-exponential factor, *EA* is the activation energy in J mol-1, *R* is the gas constant in J mol-1 K-1, *T* is the temperature in K, and *n* is the reaction or‐ der (1 for first-order, 0 for zero-order).

Somponronnarit et al. (1998) stated that the yellowing rate of paddy can be explained by temperature and water activity and developed the following empirical equations to predict the change in the yellow colour:

$$\frac{\mathbf{d}b}{\mathbf{d}t} = k \tag{29}$$

and

Equations presented in this section confirm that the changes in germination capacity of stor‐ ed grain are lower with lower following parameters: grain temperature, grain moisture con‐ tent, mechanical damage and storage time. In general, the conclusions are the same as in previous section: longer storage times are possible with lower both grain moisture contents

At the end of the chapter it is worth to mention shortly the other grain quality criteria which

Colour of white rice is an important criterion for judging quality and price. The white colour becomes yellow after a period of storage. Dry matter loss of grain and heat liberated from its respiration and biological activities may accelerate rice yellowing. Parameters affecting the rice yellowing are temperature and relative humidity (water activity) (Soponronnarit et al.,

*A B C D E F R*<sup>2</sup>

0.25 96.676 -0.72 -0.623 0.008 0.003 0.009 0.874369

1 67.972 0.178 -1.315 -0.033 -0.002 0.022 0.963953

0.25 100.072 -0.627 -0.144 0.014 -0.004 -0.001 0.8498037

1 46.691 0.168 -0.955 -0.018 0.008 0.007 0.8205147

0.25 102.912 -1.133 -0.719 0.019 -0.024 0.022 0.95634

1 60.816 -0.15 -0.737 0.006 -0.027 0.006 0.963041

0.25 95.373 -0.941 -1.736 0.024 -0.005 0.037 0.75977

1 70.357 -1.923 -2.238 0.049 0.016 0.03 0.895284

Corn quality can mean wet-milling quality. It corresponds to the amount of survival ther‐ mo-sensitive proteins inside the grains and is very well correlated with the thermal history

The rate of quality changing can be represented with a simple zero- or first-order reaction

15 0.5 87.017 0.262 -0.572 -0.027 -0.015 0.008 0.90452

18 0.5 82.486 0.004 -0.352 1.166·10-4 -7.455·10-4 5·10-4 0.92672

21 0.5 78.891 0.084 -1.352 -0.002 -0.019 0.039 0.837519

24 0.5 69.078 -0.288 -2.259 0.012 0.021 0.034 0.971917

and temperatures and with lower levels of mechanical grain damages.

can be important to consumer and food manufacturer.

1998; Tirawanichakul et al., 2004).

**Table 4.** Values of coefficients in equation (27)

of the grains (Courtois, 1995).

(Labuza, 1980):

DML, %

310 Advances in Agrophysical Research

Mw, % w.b.

$$
\ln k = 71.87 - 25.32 \text{(RH)} - \frac{25919.13}{T} + \frac{10712.78 \text{(RH)}}{T} \tag{30}
$$

where *b* is yellowness of rice in Hunter *b* unit, *t* is the time in d, *k* is the constant value for the yellowing rate in Hunter *b* unit d-1, RH is the relative humidity in decimal, *T* is the tem‐ perature in K, and 308 K≤*T*≤338 K, 0.80≤RH≤0.95.

Courtois (1995) developed the following empirical equation to predict the change in the wetmilling quality of corn:

$$\frac{d\mathbf{Q}}{dt} = -k\_0 \exp\left(-\frac{E\_A}{RT}\right) \mathbf{Q}^2\tag{31}$$

and

$$k\_0 = -1.9561 \cdot 10^{16} + 5.4287 \cdot 10^{17}M + 6.8210 \cdot 10^{17}M^2 \tag{32}$$

where *Q* is the wet-milling quality, *t* is the time in s, *k*0 is the pre-exponential factor in s-1, *T* is the temperature in K, *M* is the grain moisture content in decimal d. b., and *R* is the gas con‐ stant in J mol-1 K-1, *EA*=-133200 J mol-1.

## **5. Conclusion**

Nowadays grain is harvested with a combine harvester. Therefore it is possible to delay the process and to harvest ripe and dry grain, without any bigger losses caused by ridging of grain, yet in certain parts polluted with green parts of plants, straws and seeds of weeds or with unripe caryopses, moisture content can even exceed 30% w. b., and temperature is of‐ ten above 30°C. This state can cause self-heating processes even when the grain itself is con‐ sidered as dry. In such grain and even in grain considered as dry, vital functions connected with metabolism still exist, namely grain respiration, growth of moulds and other microor‐ ganisms as well as growth of insects. These processes lead to a decline in the quality of grain and even to its entire damage. The intensity of these processes depends mainly on the mois‐ ture content of grain and its temperature. For the purpose of safe grain storage one ought to limit its vital functions as soon as possible through lowering moisture content and tempera‐ ture reduction. It can be realized by drying, and then cooling the grain. Due to economy in thermal energy consumption, grain is often dried with the atmospheric air or slightly heated air, but such a process runs very slowly, and grain has to stay in the drying chamber for quite a long time. During harvest, when granaries accept large quantities of harvested grain, it is not always possible to immediately clean, dry and cool the grain due to the limited ca‐ pacity of devices. Therefore there is a necessity of periodic storage of the fresh grain mass, so there is a risk that undesirable processes will occur, which can lead to a decline in quality, and even entire damage of grain. It is therefore necessary to determine the time of safe grain storage, i. e. the time in which the growth of undesirable processes does not cause any es‐ sential changes in the quality of grain. The basic criteria of determination the length of this period are: CO2production and connected with it loss of the dry matter of grain, appearance of visible moulds, and germination capacity.

[2] Abramson, D., Hulasare, R, York, R. K., White, N. D. G., Jayas, D. S. (2005). Mycotox‐ ins, ergosterol, and odor volatiles in durum wheat during granary storage at 16 % and 20 % moisture content. *Journal of Stored Products Research*, Vol. 41, No. 1, (January

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[3] Abramson, D., Hulasare, White, N. D. G., Jayas, D. S., Marquardt, R. R. (1999). Myco‐ toxin formation in hulless barley during granary storage at 15 % and 19 % moisture content. *Journal of Stored Products Research*, Vol. 35, No. 3, (July 1999), pp. 297-305,

[4] Adhikarinayake, T. B., Palipane, K. B., Müller, J. (2006). Quality change and mass loss of paddy during airtight storage in a ferro-cement bin in Sri Lanka. *Journal of Stored*

[5] Al-Yahya, S. A. (2001). Effect of storage conditions on germination in wheat. *Journal of Agronomy & Crop Science*, Vol. 186, No. 4, (June 2001), pp. 273-279, ISSN 1439-037X.

[6] Arinze, E. A., Sokhansanj, S., Schoenau, G. J. (1993). Development of optimal man‐ agement schemes for in-bin drying of canola grain (rapeseed). *Computer and Electron‐*

[7] Armitage, D. M. (1986). Pest control by cooling and ambient air drying. In: *Spoilage and Mycotoxins of Cereals and other Stored Products*, B. Flannigan, (Ed.), 13-20, CAB In‐

[8] Bailey, P. H., Smith, E. A. (1982). *Strategies for control of near-ambient grain driers – sim‐ ulation using 1968 Turnhouse (Edinburg) weather*. Dept. Note SIN/330, Scot. Inst. Agric.

[9] Black, M. (1970). Seed germination and dormancy. *Science Progress*, Vol. 58, ISSN

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[12] Brooker D. B., Bakker-Arkema, F. W., Hall, C. W. 1974. *Drying cereal grains*. AVI Publ.

[13] Christiansen, C. M., Kaufmann, H. H. (1969). *Grain storage: The role of fungi quality loss*. University of Minnesota Press, ISBN 0816605181, Minneapolis, MN, USA.

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ISSN 0022-474X.

The dependencies for determining the time of safe grain storage were discussed. The gener‐ al conclusions for all discussed criteria are the same: longer storage times are possible with lower both grain moisture contents and temperatures and with lower levels of mechanical grain damages.

## **Author details**

Agnieszka Kaleta and Krzysztof Górnicki

Faculty of Production Engineering, Warsaw University of Life Sciences, Poland

## **References**

[1] Abdullah, N., Nawawi, A., Othman, I. (2000). Fungal spoilage of starch-based foods in relation to its water activity (aw). *Journal of Stored Products Research*, Vol. 36, No. 1, (January 2000), pp. 47-54 , ISSN 0022-474X.

[2] Abramson, D., Hulasare, R, York, R. K., White, N. D. G., Jayas, D. S. (2005). Mycotox‐ ins, ergosterol, and odor volatiles in durum wheat during granary storage at 16 % and 20 % moisture content. *Journal of Stored Products Research*, Vol. 41, No. 1, (January 2005), pp. 67-76, ISSN 0022-474X.

**5. Conclusion**

312 Advances in Agrophysical Research

of visible moulds, and germination capacity.

Agnieszka Kaleta and Krzysztof Górnicki

(January 2000), pp. 47-54 , ISSN 0022-474X.

grain damages.

**Author details**

**References**

Nowadays grain is harvested with a combine harvester. Therefore it is possible to delay the process and to harvest ripe and dry grain, without any bigger losses caused by ridging of grain, yet in certain parts polluted with green parts of plants, straws and seeds of weeds or with unripe caryopses, moisture content can even exceed 30% w. b., and temperature is of‐ ten above 30°C. This state can cause self-heating processes even when the grain itself is con‐ sidered as dry. In such grain and even in grain considered as dry, vital functions connected with metabolism still exist, namely grain respiration, growth of moulds and other microor‐ ganisms as well as growth of insects. These processes lead to a decline in the quality of grain and even to its entire damage. The intensity of these processes depends mainly on the mois‐ ture content of grain and its temperature. For the purpose of safe grain storage one ought to limit its vital functions as soon as possible through lowering moisture content and tempera‐ ture reduction. It can be realized by drying, and then cooling the grain. Due to economy in thermal energy consumption, grain is often dried with the atmospheric air or slightly heated air, but such a process runs very slowly, and grain has to stay in the drying chamber for quite a long time. During harvest, when granaries accept large quantities of harvested grain, it is not always possible to immediately clean, dry and cool the grain due to the limited ca‐ pacity of devices. Therefore there is a necessity of periodic storage of the fresh grain mass, so there is a risk that undesirable processes will occur, which can lead to a decline in quality, and even entire damage of grain. It is therefore necessary to determine the time of safe grain storage, i. e. the time in which the growth of undesirable processes does not cause any es‐ sential changes in the quality of grain. The basic criteria of determination the length of this period are: CO2production and connected with it loss of the dry matter of grain, appearance

The dependencies for determining the time of safe grain storage were discussed. The gener‐ al conclusions for all discussed criteria are the same: longer storage times are possible with lower both grain moisture contents and temperatures and with lower levels of mechanical

[1] Abdullah, N., Nawawi, A., Othman, I. (2000). Fungal spoilage of starch-based foods in relation to its water activity (aw). *Journal of Stored Products Research*, Vol. 36, No. 1,

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**Chapter 13**

**Extrusion-Cooking of Starch**

L. Moscicki, M. Mitrus, A. Wojtowicz,

Additional information is available at the end of the chapter

the production of so called engineered food and special feed.

ties of the extrudates in comparison to raw materials used.

most popular extrusion-cooked products are following:

The extrusion technology, well-known in the plastic industry, has recently become widely used in food industry, where it is referred to as extrusion-cooking. It has been employed for

Generally speaking, extrusion-cooking of vegetable raw materials consists in the extrusion of grinded material at baro-thermal conditions. With the help of shear energy, exerted by the rotating screw, and additional heating by the barrel, the food material is heated to its melting point, than is conveyed under high pressure through a series of dies and the prod‐ uct expands to its final shape. That results in much different physical and chemical proper‐

Food extruders – processing machines (see fig. 1), belong to the family of HTST (High Tem‐ perature Short Time) equipment, with a capability to perform cooking tasks under high pressure. This aspect may be explained for vulnerable food and feed as an advantageous process since small time span exposures to high temperatures will restrict unwanted dena‐ turation effects on e.g. proteins, amino acids, vitamins, starches and enzymes. Physical tech‐ nological aspects like heat transfer, mass transfer, momentum transfer, residence time and residence time distribution have a strong impact on the food and feed properties during ex‐ trusion-cooking and can drastically influence the final product quality (Mościcki et al., 2009,

Nowadays, extrusion-cooking as a method is used for the production of different food staff, ranging from the simplest expanded snacks to the highly-processed meat analogues. The

> © 2013 Moscicki et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2013 Moscicki et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

T. Oniszczuk and A. Rejak

http://dx.doi.org/10.5772/52323

Moscicki, 2011, Mościcki, 2011).

**1. Introduction**


## **Chapter 13**

## **Extrusion-Cooking of Starch**

L. Moscicki, M. Mitrus, A. Wojtowicz,

T. Oniszczuk and A. Rejak

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/52323

## **1. Introduction**

[64] Wieman, D. M., White, G. M., Taroba, J. L., Ross, I. J., Hicks, C. L., Langlois, B. E. (1986). Production of aflatoxin in damaged corn under controlled environmental con‐

ditions. *Transactions of the ASAE*, Vol. 29, No. 4, pp. 1150-1155, ISSN 0001-2351.

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pp. 233-238, ISSN 0045-432X.

318 Advances in Agrophysical Research

The extrusion technology, well-known in the plastic industry, has recently become widely used in food industry, where it is referred to as extrusion-cooking. It has been employed for the production of so called engineered food and special feed.

Generally speaking, extrusion-cooking of vegetable raw materials consists in the extrusion of grinded material at baro-thermal conditions. With the help of shear energy, exerted by the rotating screw, and additional heating by the barrel, the food material is heated to its melting point, than is conveyed under high pressure through a series of dies and the prod‐ uct expands to its final shape. That results in much different physical and chemical proper‐ ties of the extrudates in comparison to raw materials used.

Food extruders – processing machines (see fig. 1), belong to the family of HTST (High Tem‐ perature Short Time) equipment, with a capability to perform cooking tasks under high pressure. This aspect may be explained for vulnerable food and feed as an advantageous process since small time span exposures to high temperatures will restrict unwanted dena‐ turation effects on e.g. proteins, amino acids, vitamins, starches and enzymes. Physical tech‐ nological aspects like heat transfer, mass transfer, momentum transfer, residence time and residence time distribution have a strong impact on the food and feed properties during ex‐ trusion-cooking and can drastically influence the final product quality (Mościcki et al., 2009, Moscicki, 2011, Mościcki, 2011).

Nowadays, extrusion-cooking as a method is used for the production of different food staff, ranging from the simplest expanded snacks to the highly-processed meat analogues. The most popular extrusion-cooked products are following:

© 2013 Moscicki et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Moscicki et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**•** direct extrusion snacks, RTE (ready-to-eat) cereal flakes and diverse breakfast foods pro‐ duced from cereal material and differing in shape, colour and taste and easiest to imple‐ ment in terms of production;

**2. Starch and starchy products**

tin and its ratio in the processed material.

by amylose bounding with fatty acids or monoglycerides.

ing screw, appropriate die size, SME input, etc.

Extrusion-cooking is accompanied by the process of starch gelatinization, involving the cleavage of intermolecular hydrogen bonds. It causes a significant increase in water absorp‐ tion, including the breakage of starch granules. Gelatinized starch increases the dough vis‐ cosity, and high protein content in the processed material facilitates higher flexibility and dough aeration. After leaving the die hot material rapidly expands as a result of immediate vaporisation and takes on a porous structure. In the extruded dough protein membranes closing occur creating cell-like spaces, and starch, owing to dehydration, loses its plasticity and fixes the porous nature of the material. Rapid cooling causes the stiffening of the mass, which is typical for carbohydrate complexes embedded in a protein matrix and their total enclosure by the membrane of hydrated protein. The resulting product is structurally simi‐

Extrusion-Cooking of Starch http://dx.doi.org/10.5772/52323 321

Starch occurs primarily in cereal grains and potatoes. It takes the form of granules of differ‐ ent and characteristic shape, depending on the origin as well as on the variety and type of fertilization. As commonly known, two main components of starch are amylose and amylo‐ pectin displaying different physical and chemical properties, for example, chemical struc‐ ture. The technological assessment of extrudates takes two factors into account: the water solubility index (WSI) and the water absorption index (WAI). These properties were studied in many laboratories and the conclusions were that WAI of many starch products increases together with the temperature rising in the extruder's barrel. It has been assumed that the maximum value is obtained around the temperature ranges from 180 to 200 °C. When these temperatures are exceeded, WAI drops and causes the WSI increase. The lower material ini‐ tial moisture content used in extrusion, the higher extrudate's WSI rate can be obtained. A noticeable influence on the product properties has the percentage of amylose and amylopec‐

The extrusion processing of starchy materials certainly impacts the changes in product vis‐ cosity (pasting characteristic) after dissolving in water. This feature is very important for the technological point of view. Using Brabender viscometer we can see that the characteristic viscosity curve for starch is clearly reduced through extrusion; at the same time, the de‐ crease of viscosity is greater if higher temperatures were applied during the extrusion-cook‐ ing. The application of higher pressure during the extrusion (compression changing) does not affect the extrudate viscosity; however, it affects on viscosity stability of products re‐ tained at a temperature of 95 °C. In some cases, the properties of extrudate may be arranged

Another factor determining changes in the starch molecules during the extrusion-cooking process is the pressure and the values of existing shearing forces. In order to obtain certain technological properties of extrudates, which are often semi-finished products intended for further processing, it is necessary to set proper parameters of the extrusion process. This is achieved by the use of screws with varying compression degrees, relevant rpm of the work‐

lar to a honeycomb shaped by the clusters of molten protein fibres.


**Figure 1.** A cross-section of a single-screw extrusion-cooker: 1 - engine, 2 - feeder, 3 - cooling jacket, 4 - thermocouple, 5 – screw, 6 - barrel, 7 - heating jacket, 8 - head, 9 - net, 10 -cutter, I - transport section, II – compression section, III – melting and plasticization section (Mościcki et al., 2009).

**Figure 2.** Different type of extrusion-cooked food and feed products (Mościcki et al., 2009).

## **2. Starch and starchy products**

**•** direct extrusion snacks, RTE (ready-to-eat) cereal flakes and diverse breakfast foods pro‐ duced from cereal material and differing in shape, colour and taste and easiest to imple‐

**•** snack pellets - half products suitable for fried or hot air expanded snacks, pre-cooked pasta;

**•** textured vegetable protein (mainly from soybeans, though not always) used in the pro‐

**•** baro-thermally processed vegetable components for the pharmaceutical, chemical, paper

**Figure 1.** A cross-section of a single-screw extrusion-cooker: 1 - engine, 2 - feeder, 3 - cooling jacket, 4 - thermocouple, 5 – screw, 6 - barrel, 7 - heating jacket, 8 - head, 9 - net, 10 -cutter, I - transport section, II – compression section, III –

**•** baby food, pre-cooked flours, instant concentrates, functional components;

**•** confectionery: different kinds of sweets, chewing gum, and many others.

**Figure 2.** Different type of extrusion-cooked food and feed products (Mościcki et al., 2009).

**•** pet food, aquafeed, feed concentrates and calf-milk replacers;

**•** crispy bread, bread crumbs, emulsions and pastes;

melting and plasticization section (Mościcki et al., 2009).

ment in terms of production;

320 Advances in Agrophysical Research

duction of meat analogues;

and brewing industry;

Extrusion-cooking is accompanied by the process of starch gelatinization, involving the cleavage of intermolecular hydrogen bonds. It causes a significant increase in water absorp‐ tion, including the breakage of starch granules. Gelatinized starch increases the dough vis‐ cosity, and high protein content in the processed material facilitates higher flexibility and dough aeration. After leaving the die hot material rapidly expands as a result of immediate vaporisation and takes on a porous structure. In the extruded dough protein membranes closing occur creating cell-like spaces, and starch, owing to dehydration, loses its plasticity and fixes the porous nature of the material. Rapid cooling causes the stiffening of the mass, which is typical for carbohydrate complexes embedded in a protein matrix and their total enclosure by the membrane of hydrated protein. The resulting product is structurally simi‐ lar to a honeycomb shaped by the clusters of molten protein fibres.

Starch occurs primarily in cereal grains and potatoes. It takes the form of granules of differ‐ ent and characteristic shape, depending on the origin as well as on the variety and type of fertilization. As commonly known, two main components of starch are amylose and amylo‐ pectin displaying different physical and chemical properties, for example, chemical struc‐ ture. The technological assessment of extrudates takes two factors into account: the water solubility index (WSI) and the water absorption index (WAI). These properties were studied in many laboratories and the conclusions were that WAI of many starch products increases together with the temperature rising in the extruder's barrel. It has been assumed that the maximum value is obtained around the temperature ranges from 180 to 200 °C. When these temperatures are exceeded, WAI drops and causes the WSI increase. The lower material ini‐ tial moisture content used in extrusion, the higher extrudate's WSI rate can be obtained. A noticeable influence on the product properties has the percentage of amylose and amylopec‐ tin and its ratio in the processed material.

The extrusion processing of starchy materials certainly impacts the changes in product vis‐ cosity (pasting characteristic) after dissolving in water. This feature is very important for the technological point of view. Using Brabender viscometer we can see that the characteristic viscosity curve for starch is clearly reduced through extrusion; at the same time, the de‐ crease of viscosity is greater if higher temperatures were applied during the extrusion-cook‐ ing. The application of higher pressure during the extrusion (compression changing) does not affect the extrudate viscosity; however, it affects on viscosity stability of products re‐ tained at a temperature of 95 °C. In some cases, the properties of extrudate may be arranged by amylose bounding with fatty acids or monoglycerides.

Another factor determining changes in the starch molecules during the extrusion-cooking process is the pressure and the values of existing shearing forces. In order to obtain certain technological properties of extrudates, which are often semi-finished products intended for further processing, it is necessary to set proper parameters of the extrusion process. This is achieved by the use of screws with varying compression degrees, relevant rpm of the work‐ ing screw, appropriate die size, SME input, etc.

## **3. Starch transformation by thermo-mechanical treatment**

Starch can be modifying by enzymatic, chemical or physical methods depend on processing and application fields of final products. Different types of processing, based on disruption and melting the semi-crystalline structure of starch may be used to transformation of native starch to form a thermoplastic starch (TPS) starch. Thermo-mechanical treatment that com‐ bines temperature and shear stress, like extrusion or injection moulding, is useful to trans‐ form granular starch into TPS. TPS modify by these methods may be applied as basic raw material or partial replacement of plastics for packaging materials applications in selected areas of food industry, horticulture, agriculture, but also for biomedical and cosmetic indus‐ tries as gels, foams, films or in the form of a membrane with defined properties or biode‐ gradability (Yimlaz, 2003).

compression moulding device. All these devises can simulate to a certain extent different temperature and treating time processes i.e. mixing-kneading, extrusion-cooking or injection moulding (Yimlaz, 2003, Peighambardoust et al., 2004, Peighambardoust et al., 2007, van den Einde et al., 2004, van den Veen, 2005). The shear rate, temperature profile, residence time during treatment influence simultaneously the starch behaviour and properties. Also in these research results the changes in properties in excess of water were observed. Most stud‐ ies on the influence of water on the properties were carried out at high water content, but it is well known that extrusion-cooking or injection moulding processes are done with a limit‐ ed (10-30%) water content. Properties of products can be measured by WAXS or intrinsic viscosity (Barron et al., 2000). Product behaviour and properties after extrusion with a high level of water content are not always acceptable because of crystallinity, retrogradation and stress-strain profiles of the materials expressed by the tensile strength or elongation (van So‐ est & Knooren, 1997). Depending on the amount of glycerol in TPS the product may be in its glassy or rubbery state at ambient temperature (Yimlaz, 2003). In the presence of sufficient water or glycerol under gelatinization conditions native starch becomes gel-like in appear‐ ance or properties but during the thermoplastic processing behaves like a polymer melt. The tests with different starch origins can be found in literature (Yimlaz, 2003, Peighambardoust

Extrusion-Cooking of Starch http://dx.doi.org/10.5772/52323 323

Tests of starch melting usually are performed in a two-bladed counter rotating batch mixer Brabender Mixograph simulating mixing-kneading conditions interfaced with a computer and control unit. Wójtowicz (2009) tested various starches with water and glycerol accord‐ ing to following procedure: mixer temperature was set to 85 °C and heating was started di‐ rectly after chamber closing and rotation of screws was increased from 5 to 100 rpm during 3 minutes. Comparison of starches origins were performed at the same temperature-time but screw rotation increased from 5 to 80 rpm. Samples were treated during 10 minutes in

In the study presented by Wójtowicz & van der Goot (2005) investigations results on similar starch–glycerol mixtures with limited water addition (below 30%) subjected on the heating and shearing behaviour are presented. The purpose of the treatment was to use special de‐ signed shearing device - Shear Cell for obtains a starchy molten phase under thermo-me‐ chanical processing similar to extrusion. This new equipment is based on the cone and plate rheometer ideology on a pilot scale (Figure 3). There is possibility to isolate singular param‐ eters during processing like temperature, rotation speed or shear stress in this equipment (van den Einde et al., 2003). The details of this shearing device can be found elsewhere (Peighambardoust et al., 2004, van den Einde et al., 2004, van den Veen et al., 2004). The based material was potato starch with addition of glycerol 20-25% and with 5-20% amount of added water (w/w). Treatment temperature was selected on 85 °C for samples with 15 and 20% of water added, 88 °C for samples with 5 and 10% of water added and 115 °C for starch – glycerol mixtures. The rotation speed was 10 rpm during first 2 minutes and in‐ creased simultaneously to 100 rpm during 3 minutes. The torque changes during the treat‐

et al., 2004, van den Einde et al., 2004).

ment were recorded.

total. During mixing the torque was recorded continuously.

Starch modification with thermomechanical treatment is difficult because of important in‐ crease of starch viscosity during heating and shearing, what may be the reason of uncon‐ trolled dextrin's formation and browning reaction, especially when temperature above 100 °C is used. Some kind of plasticizers may improve intensity of starch transforma‐ tions, i.e. water is most commonly used and the minimum moisture content required for starch gelatinization is around 33%. There are many studies about the different transfor‐ mations of starchy material to thermoplastic forms with intermediate and high water lev‐ el. High water content in the mixture also influences the onset temperature, glass transition temperature and rheological properties of molten materials (Della Valle et al., 1995, Igura et al, 2001, Nashed et al., 2003, van Soest et al., 1996a). In many scientific publications also other plasticizers were examined i.e. monoglycerides or glycerol, as flexibility improvers (Schogren, 1993). Addition of glycerol is of influenced on the onset of gelatinization and results in an increase in the activation energy for the melting of the starch crystallites and results in higher glass transition temperatures and higher interac‐ tions forces between glycerol and starch polymers (Della Valle et al., 1995, van Soest & Knooren, 1997, van Soest et al., 1996b, You et al., 2003). During the extrusion process high shear stresses and high values of energy input take place and under these condi‐ tions the melting process may be enhanced (Della Valle et al., 1995). Specific mechanical energy (SME) values necessary to transformations decrease with increasing water level in raw material. Corn or waxy corn and wheat or barley starch were most often investigat‐ ed as basic thermoplastic raw materials (Nashed et al., 2003, Barron et al., 2000).

Modifications in the presence of plasticizers can be done by thermomechanical processing techniques like heating, kneading, injection, compression or vacuum moulding or extrusion below 150 °C (Yimlaz, 2003). Depending on the starch origin some specific differences are observed. Wheat, corn or potato starches behave different for different plasticisers or lubri‐ cants content and different processing conditions.

Test results achieved with different types of rheometers used to simulate the thermome‐ chanical conditions differ and depend on the equipment used. The influence of the intensity of the treatment can be tested with a batch mixer, a cone and plate rheometer, a Shear Cell device with well defined shear rate, a Couette-type device with variable eccentricity or a compression moulding device. All these devises can simulate to a certain extent different temperature and treating time processes i.e. mixing-kneading, extrusion-cooking or injection moulding (Yimlaz, 2003, Peighambardoust et al., 2004, Peighambardoust et al., 2007, van den Einde et al., 2004, van den Veen, 2005). The shear rate, temperature profile, residence time during treatment influence simultaneously the starch behaviour and properties. Also in these research results the changes in properties in excess of water were observed. Most stud‐ ies on the influence of water on the properties were carried out at high water content, but it is well known that extrusion-cooking or injection moulding processes are done with a limit‐ ed (10-30%) water content. Properties of products can be measured by WAXS or intrinsic viscosity (Barron et al., 2000). Product behaviour and properties after extrusion with a high level of water content are not always acceptable because of crystallinity, retrogradation and stress-strain profiles of the materials expressed by the tensile strength or elongation (van So‐ est & Knooren, 1997). Depending on the amount of glycerol in TPS the product may be in its glassy or rubbery state at ambient temperature (Yimlaz, 2003). In the presence of sufficient water or glycerol under gelatinization conditions native starch becomes gel-like in appear‐ ance or properties but during the thermoplastic processing behaves like a polymer melt. The tests with different starch origins can be found in literature (Yimlaz, 2003, Peighambardoust et al., 2004, van den Einde et al., 2004).

**3. Starch transformation by thermo-mechanical treatment**

gradability (Yimlaz, 2003).

322 Advances in Agrophysical Research

Starch can be modifying by enzymatic, chemical or physical methods depend on processing and application fields of final products. Different types of processing, based on disruption and melting the semi-crystalline structure of starch may be used to transformation of native starch to form a thermoplastic starch (TPS) starch. Thermo-mechanical treatment that com‐ bines temperature and shear stress, like extrusion or injection moulding, is useful to trans‐ form granular starch into TPS. TPS modify by these methods may be applied as basic raw material or partial replacement of plastics for packaging materials applications in selected areas of food industry, horticulture, agriculture, but also for biomedical and cosmetic indus‐ tries as gels, foams, films or in the form of a membrane with defined properties or biode‐

Starch modification with thermomechanical treatment is difficult because of important in‐ crease of starch viscosity during heating and shearing, what may be the reason of uncon‐ trolled dextrin's formation and browning reaction, especially when temperature above 100 °C is used. Some kind of plasticizers may improve intensity of starch transforma‐ tions, i.e. water is most commonly used and the minimum moisture content required for starch gelatinization is around 33%. There are many studies about the different transfor‐ mations of starchy material to thermoplastic forms with intermediate and high water lev‐ el. High water content in the mixture also influences the onset temperature, glass transition temperature and rheological properties of molten materials (Della Valle et al., 1995, Igura et al, 2001, Nashed et al., 2003, van Soest et al., 1996a). In many scientific publications also other plasticizers were examined i.e. monoglycerides or glycerol, as flexibility improvers (Schogren, 1993). Addition of glycerol is of influenced on the onset of gelatinization and results in an increase in the activation energy for the melting of the starch crystallites and results in higher glass transition temperatures and higher interac‐ tions forces between glycerol and starch polymers (Della Valle et al., 1995, van Soest & Knooren, 1997, van Soest et al., 1996b, You et al., 2003). During the extrusion process high shear stresses and high values of energy input take place and under these condi‐ tions the melting process may be enhanced (Della Valle et al., 1995). Specific mechanical energy (SME) values necessary to transformations decrease with increasing water level in raw material. Corn or waxy corn and wheat or barley starch were most often investigat‐

ed as basic thermoplastic raw materials (Nashed et al., 2003, Barron et al., 2000).

cants content and different processing conditions.

Modifications in the presence of plasticizers can be done by thermomechanical processing techniques like heating, kneading, injection, compression or vacuum moulding or extrusion below 150 °C (Yimlaz, 2003). Depending on the starch origin some specific differences are observed. Wheat, corn or potato starches behave different for different plasticisers or lubri‐

Test results achieved with different types of rheometers used to simulate the thermome‐ chanical conditions differ and depend on the equipment used. The influence of the intensity of the treatment can be tested with a batch mixer, a cone and plate rheometer, a Shear Cell device with well defined shear rate, a Couette-type device with variable eccentricity or a Tests of starch melting usually are performed in a two-bladed counter rotating batch mixer Brabender Mixograph simulating mixing-kneading conditions interfaced with a computer and control unit. Wójtowicz (2009) tested various starches with water and glycerol accord‐ ing to following procedure: mixer temperature was set to 85 °C and heating was started di‐ rectly after chamber closing and rotation of screws was increased from 5 to 100 rpm during 3 minutes. Comparison of starches origins were performed at the same temperature-time but screw rotation increased from 5 to 80 rpm. Samples were treated during 10 minutes in total. During mixing the torque was recorded continuously.

In the study presented by Wójtowicz & van der Goot (2005) investigations results on similar starch–glycerol mixtures with limited water addition (below 30%) subjected on the heating and shearing behaviour are presented. The purpose of the treatment was to use special de‐ signed shearing device - Shear Cell for obtains a starchy molten phase under thermo-me‐ chanical processing similar to extrusion. This new equipment is based on the cone and plate rheometer ideology on a pilot scale (Figure 3). There is possibility to isolate singular param‐ eters during processing like temperature, rotation speed or shear stress in this equipment (van den Einde et al., 2003). The details of this shearing device can be found elsewhere (Peighambardoust et al., 2004, van den Einde et al., 2004, van den Veen et al., 2004). The based material was potato starch with addition of glycerol 20-25% and with 5-20% amount of added water (w/w). Treatment temperature was selected on 85 °C for samples with 15 and 20% of water added, 88 °C for samples with 5 and 10% of water added and 115 °C for starch – glycerol mixtures. The rotation speed was 10 rpm during first 2 minutes and in‐ creased simultaneously to 100 rpm during 3 minutes. The torque changes during the treat‐ ment were recorded.

low amount 5% of water added showed the highest values of torque and increasing the wa‐

Extrusion-Cooking of Starch http://dx.doi.org/10.5772/52323 325

**Figure 4.** Torque values during mixing-kneading of various starch origins with 20% of glycerol addition and different

Differences between curves in Fig. 5 and 6 may be important for definition of shearing influ‐ ence on samples behaviour and properties. Also time of the beginning of rheological changes is similar except sample with 5% of added water. During intensive thermomechani‐ cal treatment in the Shear Cell shorter time required to starting changes inside the structure is observed. It may be explained much higher shear stress during shearing-heating in Shear Cell (Wójtowicz, 2009). It was not possible to start the melting process in potato starch-glyc‐ erol mixture without water addition because of to low temperature of heating in Brabender device equipped with water heating system and maximum temperature which can be ach‐ ieved is 98 °C during heating. After tests in Shear Cell it is known now that start-melting

It is also important that increasing of total amount of plasticizers (water and glycerol) influ‐ enced on lower torque values during measurements, as showed on the Figure 7 and 8. In‐ creased glycerol addition also has a strong effect on torque results. Nashed et al. (2003) reported through DSC that glycerol behaves as an anti-plasticizer because of hindering the gelatinization process and linear increase of onset temperature with increasing glycerol con‐ tent was observed during treatment of wheat starch-water-glycerol mixtures. During ther‐ mo-mechanical treatment of starch-glycerol mixtures it was clear that higher glycerol addition influenced on decreasing melting or gelatinization time and temperature and also

temperature for these recipes is about 115 °C (Wójtowicz& van der Goot, 2005).

torque during treatment decreased (Wójtowicz & van der Goot, 2005).

ter content influence on lower torque in both types of treatment.

level of water added (Wójtowicz, 2009)

**Figure 3.** Shear Cell equipment scheme and after starch processing: 1- shearing zone, 2 – heating elements, 3 – rotat‐ ing plate, 4 – non-rotating cone, 5 – thermocouple, 6 – torque measurement point. Cone angle = 100°, shear zone angle = 2,5°, r = 0,1 m, h = 0,082 m (Wójtowicz & van der Goot, 2005)

Research results showed that the addition of water in amount from 5 to 20% influenced on almost every recorded parameter during treatment in Brabender Mixograph. During treatment starch-glycerol-water mixtures it was observed decreasing start melting tem‐ perature from 80 °C for mixtures with limited water addition (5%) to 65-70 °C for sam‐ ples with 20% of added water. Also the time needed to start melting of samples decreased with increasing of water addition. It seems to be that water becomes a plasti‐ cizer for starch and this is in accordance with previous reports (van Soest et al., 1996a). Also the effect of water addition on torque values and decrease of torque with increas‐ ing water content in mixtures was observed.

It was also found that potato starch required lower melting temperature than wheat and corn starch with glycerol and water addition but simultaneously higher maximum torque values were reported during the melting tests. The lowest torque values were reached for corn starch samples independent on water addition. The temperature range needed to melt‐ ing beginning was 80-95 °C for corn starch-glycerol mixtures, 78-91 °C for wheat starch-glyc‐ erol mixtures and 78-88 °C for potato starch-glycerol mixtures mixed under 80 rpm used, depend on water content in the treated sample. Higher water level influences on lower tem‐ perature reached and lower max torque values during tests (Fig. 4).

During the tests the effect of water addition on torque values and decrease of torque with increasing water content in mixtures was observed. Torque values reported for mixingkneading were quite low comparing the extrusion process and Shear Cell treatment. On the Figure 5 and 6 there are shown potato starch-glycerol (80-20) mixtures behaviours during treatment with different water addition in similar condition (85 °C heating temperature and 100 rpm) in Brabender Mixograpf and Shear Cell, respectively. Unfortunately mixtures with low amount 5% of water added showed the highest values of torque and increasing the wa‐ ter content influence on lower torque in both types of treatment.

**Figure 3.** Shear Cell equipment scheme and after starch processing: 1- shearing zone, 2 – heating elements, 3 – rotat‐ ing plate, 4 – non-rotating cone, 5 – thermocouple, 6 – torque measurement point. Cone angle = 100°, shear zone

Research results showed that the addition of water in amount from 5 to 20% influenced on almost every recorded parameter during treatment in Brabender Mixograph. During treatment starch-glycerol-water mixtures it was observed decreasing start melting tem‐ perature from 80 °C for mixtures with limited water addition (5%) to 65-70 °C for sam‐ ples with 20% of added water. Also the time needed to start melting of samples decreased with increasing of water addition. It seems to be that water becomes a plasti‐ cizer for starch and this is in accordance with previous reports (van Soest et al., 1996a). Also the effect of water addition on torque values and decrease of torque with increas‐

It was also found that potato starch required lower melting temperature than wheat and corn starch with glycerol and water addition but simultaneously higher maximum torque values were reported during the melting tests. The lowest torque values were reached for corn starch samples independent on water addition. The temperature range needed to melt‐ ing beginning was 80-95 °C for corn starch-glycerol mixtures, 78-91 °C for wheat starch-glyc‐ erol mixtures and 78-88 °C for potato starch-glycerol mixtures mixed under 80 rpm used, depend on water content in the treated sample. Higher water level influences on lower tem‐

During the tests the effect of water addition on torque values and decrease of torque with increasing water content in mixtures was observed. Torque values reported for mixingkneading were quite low comparing the extrusion process and Shear Cell treatment. On the Figure 5 and 6 there are shown potato starch-glycerol (80-20) mixtures behaviours during treatment with different water addition in similar condition (85 °C heating temperature and 100 rpm) in Brabender Mixograpf and Shear Cell, respectively. Unfortunately mixtures with

angle = 2,5°, r = 0,1 m, h = 0,082 m (Wójtowicz & van der Goot, 2005)

324 Advances in Agrophysical Research

ing water content in mixtures was observed.

perature reached and lower max torque values during tests (Fig. 4).

**Figure 4.** Torque values during mixing-kneading of various starch origins with 20% of glycerol addition and different level of water added (Wójtowicz, 2009)

Differences between curves in Fig. 5 and 6 may be important for definition of shearing influ‐ ence on samples behaviour and properties. Also time of the beginning of rheological changes is similar except sample with 5% of added water. During intensive thermomechani‐ cal treatment in the Shear Cell shorter time required to starting changes inside the structure is observed. It may be explained much higher shear stress during shearing-heating in Shear Cell (Wójtowicz, 2009). It was not possible to start the melting process in potato starch-glyc‐ erol mixture without water addition because of to low temperature of heating in Brabender device equipped with water heating system and maximum temperature which can be ach‐ ieved is 98 °C during heating. After tests in Shear Cell it is known now that start-melting temperature for these recipes is about 115 °C (Wójtowicz& van der Goot, 2005).

It is also important that increasing of total amount of plasticizers (water and glycerol) influ‐ enced on lower torque values during measurements, as showed on the Figure 7 and 8. In‐ creased glycerol addition also has a strong effect on torque results. Nashed et al. (2003) reported through DSC that glycerol behaves as an anti-plasticizer because of hindering the gelatinization process and linear increase of onset temperature with increasing glycerol con‐ tent was observed during treatment of wheat starch-water-glycerol mixtures. During ther‐ mo-mechanical treatment of starch-glycerol mixtures it was clear that higher glycerol addition influenced on decreasing melting or gelatinization time and temperature and also torque during treatment decreased (Wójtowicz & van der Goot, 2005).

haves flexible and easy undergo elongation and formation different shapes. After cooling at room temperature material became hard to formulation, and no more flexible. All the sam‐ ples with addition of glycerol and heated-sheared in the Shear Cell had visibly transparent glassy-like appearance and smooth surface, directly after processing in worm stage they were easily to elongation, showed rubbery properties and they were longer elastic after cooling to room temperature (Wójtowicz & van der Goot, 2005). This phenomenon may be the result of pressure differences between both types of equipment during processing, in Shear Cell the pressure was much higher than in mixer and air bubbles or steam formed in transformed material disappeared pushed out through silicone seal by pressure inside the apparatus. Mixing-kneading equipment had lower pressure in testing chamber and it was not possible venting processed material, it may be the reasons of foamy structure of modify

Extrusion-Cooking of Starch http://dx.doi.org/10.5772/52323 327

**Figure 7.** Torque values during treatment in the Brabender Mixograph of potato starch-glycerol (75-25) mixtures with

The intrinsic viscosity of starch (*η*) is very sensitive for thermomechanical treatment and the degradation of molecular weight compounds in starch, therefore it can be used as a method to molecular weight measurement. The authors (Wójtowicz & van der Goot, 2005) report an intrinsic viscosity of native starch and sheared-heated samples measured according the Ub‐

Intrinsic viscosity of native potato starch was 369,8 ml/g. Intrinsic viscosity of samples treat‐ ed in Brabender Mixograph varied from 174 ml/g for starch-glycerol (80:20) mixtures with 5% water added to 202 ml/g for starch-glycerol (75:25) with 20% water added. These values compare to native starch were much lower and it may suggest breakdown of starch granules during Brabender treatment. But differences between samples were smaller than observed after shearing-heating process in Shear Cell. Results for samples processed in Shear Cell also were lower than for native starch and values variation was between 108 for samples of starch-glycerol (80:20) mixtures with 10% water added and 215 ml/g for starch-glycerol

belohde viscometer method (Cunningham, 1996) at 25 °C.

starch.

different water addition

**Figure 5.** Torque values during treatment in the Brabender Mixograph of potato starch-glycerol (80-20) mixtures with different water addition (Wójtowicz, 2009)

**Figure 6.** Torque values during treatment in the Shear Cell of potato starch-glycerol (80-20) mixtures with different water addition (Wójtowicz & van der Goot, 2005)

Wójtowicz and van der Goot (2005) noted that there were also visible differences in trans‐ parency and flexibility of achieved samples after different treatment type (Fig. 9). After mix‐ ing-kneading in Brabender equipment samples became elastic, with foam consistency and non-transparent, milky white colour. Only for samples of potato starch with small amount of water added material became a little brittle and partially transparent with 5% added wa‐ ter and completely transparent, glassy look like with higher level of water added. But these last samples were much stickier after treatment then the others. When they were warm be‐ haves flexible and easy undergo elongation and formation different shapes. After cooling at room temperature material became hard to formulation, and no more flexible. All the sam‐ ples with addition of glycerol and heated-sheared in the Shear Cell had visibly transparent glassy-like appearance and smooth surface, directly after processing in worm stage they were easily to elongation, showed rubbery properties and they were longer elastic after cooling to room temperature (Wójtowicz & van der Goot, 2005). This phenomenon may be the result of pressure differences between both types of equipment during processing, in Shear Cell the pressure was much higher than in mixer and air bubbles or steam formed in transformed material disappeared pushed out through silicone seal by pressure inside the apparatus. Mixing-kneading equipment had lower pressure in testing chamber and it was not possible venting processed material, it may be the reasons of foamy structure of modify starch.

**Figure 5.** Torque values during treatment in the Brabender Mixograph of potato starch-glycerol (80-20) mixtures with

**Figure 6.** Torque values during treatment in the Shear Cell of potato starch-glycerol (80-20) mixtures with different

Wójtowicz and van der Goot (2005) noted that there were also visible differences in trans‐ parency and flexibility of achieved samples after different treatment type (Fig. 9). After mix‐ ing-kneading in Brabender equipment samples became elastic, with foam consistency and non-transparent, milky white colour. Only for samples of potato starch with small amount of water added material became a little brittle and partially transparent with 5% added wa‐ ter and completely transparent, glassy look like with higher level of water added. But these last samples were much stickier after treatment then the others. When they were warm be‐

different water addition (Wójtowicz, 2009)

326 Advances in Agrophysical Research

water addition (Wójtowicz & van der Goot, 2005)

**Figure 7.** Torque values during treatment in the Brabender Mixograph of potato starch-glycerol (75-25) mixtures with different water addition

The intrinsic viscosity of starch (*η*) is very sensitive for thermomechanical treatment and the degradation of molecular weight compounds in starch, therefore it can be used as a method to molecular weight measurement. The authors (Wójtowicz & van der Goot, 2005) report an intrinsic viscosity of native starch and sheared-heated samples measured according the Ub‐ belohde viscometer method (Cunningham, 1996) at 25 °C.

Intrinsic viscosity of native potato starch was 369,8 ml/g. Intrinsic viscosity of samples treat‐ ed in Brabender Mixograph varied from 174 ml/g for starch-glycerol (80:20) mixtures with 5% water added to 202 ml/g for starch-glycerol (75:25) with 20% water added. These values compare to native starch were much lower and it may suggest breakdown of starch granules during Brabender treatment. But differences between samples were smaller than observed after shearing-heating process in Shear Cell. Results for samples processed in Shear Cell also were lower than for native starch and values variation was between 108 for samples of starch-glycerol (80:20) mixtures with 10% water added and 215 ml/g for starch-glycerol (75:25) without water added (Wójtowicz & van der Goot, 2005). It means that during shear‐ ing-heating treatment in Shear Cell high macromolecular degradation takes place. Intrinsic viscosity values were slightly dependent on glycerol content in mixtures and with increas‐ ing glycerol content decrease of intrinsic viscosity were observed in potato starch-glycerolwater mixtures treated in the Shear Cell under similar conditions.

These results are in accordance with Fujio et al. (1995) for potato, corn and wheat starches, van den Einde et al. (2003) for cornstarch and also Rushing & Hester (2003) for polymers. Intrinsic viscosity is very sensitive especially on thermomechanical degradation. Low values of shear stress influenced on lower intrinsic viscosity of treated starch-glycerol mixtures. But in all cases variations between intrinsic viscosity's values are quite small and it can be con‐ cluded that almost the same degree of starch molecules degradation was noted. In compar‐ ing with native starch intrinsic viscosity values reduced over 50%, so residue starch molecules was broken by thermomechanical treatment. By comparing those data with data generated by van den Einde et al. (2003), it can be concluded that potato starch was less ther‐

Extrusion-Cooking of Starch http://dx.doi.org/10.5772/52323 329

Native starch is not always suitable for practical use. Therefore, various starch modification techniques have been developed for food and non-food applications. Generally there are chemical methods. In many cases, especially in the food sector, chemically modified starch can be replaced by that extrusion-cooked. During the extrusion-cooking physical and chemi‐ cal transformation of starch takes place and no chemicals are needed. Baro-thermal treat‐ ment causes gelatinisation of starch, accompanied by rupture of intermolecular bonds,

The degree of changes in starch depends on properly selected process parameters and the residence time of raw material in the extruder. That allows us to create the expected proper‐ ties of the obtained modified starches, including the degree of gelatinization and viscosity of the gels. These products may find wide application in food industry as food additives, very often by replacing chemically modified starchy products. Extrusion-cooked starch may find its use as a component of food products in the manufacture of instant products, different kinds of fillings in the confectionery industry, as a gelling agent, structure stabilizer and wa‐ ter- or fat-absorbent fillers. That may be very attractive from the consumer point of view. Application extrusion-cooking is a relatively cheap alternative in the production of modified

Potato starch Superior type was purchased from PEPEES Company (Lomza, Poland). Its moisture content was 17%. During the extrusion-cooking process the 4 levels of moisture

Extrusion-cooking of potato starch was carried out using a modified single screw extrusioncooker TS-45 (Polish design) with L / D = 16, and the die with one opening with a diameter of 3 mm was uses. During the study three temperature of extrusion process (100, 120 and 140 °C) and a variable screw's speed (1.00, 1.33, 1.66 and 2.00 s-1) were used. The process en‐ ergy consumption was measured with a wattmeter connected to the extruder and the specif‐

resulting in rupture of starch grains and significantly increase of water absorption.

mostable than corn starch.

starches.

**4.1. Materials and methods**

**4. Starch modification by extrusion-cooking**

content of raw material (17, 20, 25 and 30%) were used.

**Figure 8.** Torque values during treatment in the Shear Cell of potato starch-glycerol (75-25) mixtures with different water addition

**Figure 9.** Overview of samples after treatment in: a) BrabenderMixograph, b) Shear Cell

These results are in accordance with Fujio et al. (1995) for potato, corn and wheat starches, van den Einde et al. (2003) for cornstarch and also Rushing & Hester (2003) for polymers. Intrinsic viscosity is very sensitive especially on thermomechanical degradation. Low values of shear stress influenced on lower intrinsic viscosity of treated starch-glycerol mixtures. But in all cases variations between intrinsic viscosity's values are quite small and it can be con‐ cluded that almost the same degree of starch molecules degradation was noted. In compar‐ ing with native starch intrinsic viscosity values reduced over 50%, so residue starch molecules was broken by thermomechanical treatment. By comparing those data with data generated by van den Einde et al. (2003), it can be concluded that potato starch was less ther‐ mostable than corn starch.

## **4. Starch modification by extrusion-cooking**

Native starch is not always suitable for practical use. Therefore, various starch modification techniques have been developed for food and non-food applications. Generally there are chemical methods. In many cases, especially in the food sector, chemically modified starch can be replaced by that extrusion-cooked. During the extrusion-cooking physical and chemi‐ cal transformation of starch takes place and no chemicals are needed. Baro-thermal treat‐ ment causes gelatinisation of starch, accompanied by rupture of intermolecular bonds, resulting in rupture of starch grains and significantly increase of water absorption.

The degree of changes in starch depends on properly selected process parameters and the residence time of raw material in the extruder. That allows us to create the expected proper‐ ties of the obtained modified starches, including the degree of gelatinization and viscosity of the gels. These products may find wide application in food industry as food additives, very often by replacing chemically modified starchy products. Extrusion-cooked starch may find its use as a component of food products in the manufacture of instant products, different kinds of fillings in the confectionery industry, as a gelling agent, structure stabilizer and wa‐ ter- or fat-absorbent fillers. That may be very attractive from the consumer point of view. Application extrusion-cooking is a relatively cheap alternative in the production of modified starches.

#### **4.1. Materials and methods**

(75:25) without water added (Wójtowicz & van der Goot, 2005). It means that during shear‐ ing-heating treatment in Shear Cell high macromolecular degradation takes place. Intrinsic viscosity values were slightly dependent on glycerol content in mixtures and with increas‐ ing glycerol content decrease of intrinsic viscosity were observed in potato starch-glycerol-

**Figure 8.** Torque values during treatment in the Shear Cell of potato starch-glycerol (75-25) mixtures with different

**Figure 9.** Overview of samples after treatment in: a) BrabenderMixograph, b) Shear Cell

water mixtures treated in the Shear Cell under similar conditions.

water addition

328 Advances in Agrophysical Research

Potato starch Superior type was purchased from PEPEES Company (Lomza, Poland). Its moisture content was 17%. During the extrusion-cooking process the 4 levels of moisture content of raw material (17, 20, 25 and 30%) were used.

Extrusion-cooking of potato starch was carried out using a modified single screw extrusioncooker TS-45 (Polish design) with L / D = 16, and the die with one opening with a diameter of 3 mm was uses. During the study three temperature of extrusion process (100, 120 and 140 °C) and a variable screw's speed (1.00, 1.33, 1.66 and 2.00 s-1) were used. The process en‐ ergy consumption was measured with a wattmeter connected to the extruder and the specif‐ ic mechanical energy (SME) input was calculated (Janssen et al, 2002, Mitrus, 2005a, Mitrus & Moscicki, 2009, Wolf, 2010).

Degree of starch gelatinization was measured by enzymatic method in accordance with Pol‐ ish standard PN-A-79011-11:1998.

Cross-sectional expansion index was determined as the diameter of extrudates divided by the diameter of the matrix opening (Moscicki, 2011). Measurements were done in 10 repetitions.

Water absorption index was determined according to the method of Anderson et al. (1970) with own modification. The extrudates were crushed using a laboratory mill to particles with a diameter less than 0.3 mm. A 0.7 g ground sample was suspended in 7 ml of distilled water at 20 °C in a tared centrifuge tube, stirred intermittently over a 10 min period. The resulting suspension was centrifuged at speeds 250 s-1 for 10 minutes in T24D type centri‐ fuge. The supernatant liquid was poured into a tared evaporating dish. The remaining gel was weighted and the WAI was calculated as WAI = wg/ws(%), where wg is a weight of gel and ws is the weight of dry sample. Measurements were performed in 6 replications.

Water solubility index was determined from the amount of dried solids recovered during evaporation of supernatant obtained from the WAI analysis according to the method of Harper (1981). Results were calculated from formula WSI = wds/ws (%), where wds is the weight of dry solids of supernatant and ws is the weight of dry sample. Measurements were performed in 6 replications.

**Figure 10.** SME changes during potato starch extrusion-cooking at 120 °C

**Figure 11.** Degree of gelatinization of the potato starch extrusion-cooked at 100 °C

During our research has been noticed that the degree of potato starch gelatinization de‐ creased with increase of extrusion-cooking temperature and when processed starch con‐ tained more water (Fig. 11). That was evident especially when high rpm of the screw was

Extrusion-Cooking of Starch http://dx.doi.org/10.5772/52323 331

The data reported was subjected to analysis of variance (ANOVA) by Duncan's test (P<0.05) using SAS 9.1 software.

#### **4.2. Results and discussion**

Specific mechanical energy during potato starch extrusion-cooking depends on the process parameters. The research revealed that the values of SME were within a range 298.8-990 kJkg-1 (0.083-0.275 kWhkg-1). These values were lower than the values obtained by Della Valle et al. (1995). The lowest energy consumption was observed during the extrusion-cook‐ ing process of potato starch at 140 °C. The highest energy consumption was recorded during the extrusion-cooking process at a temperature of 100 °C (at moisture content of 17 and 20%) and at 120 °C (moisture content 25 and 30%).

Studies have shown the energy consumption dependence from extruder screw speed (Fig. 10). Effect of moisture content on the SME was inconclusive. When carrying out the process at 100 °C, little change was observed (decrease) in specific mechanical energy. At higher temperature of extrusion it was observed that an increase in moisture content of starch in‐ creases the rate of the SME. It was most likely caused by increasing viscosity of processed slurry. Due to the presence of water the starch melts and underwent liquefaction, resulting in lower glass transition temperature.

**Figure 10.** SME changes during potato starch extrusion-cooking at 120 °C

ic mechanical energy (SME) input was calculated (Janssen et al, 2002, Mitrus, 2005a, Mitrus

Degree of starch gelatinization was measured by enzymatic method in accordance with Pol‐

Cross-sectional expansion index was determined as the diameter of extrudates divided by the diameter of the matrix opening (Moscicki, 2011). Measurements were done in 10

Water absorption index was determined according to the method of Anderson et al. (1970) with own modification. The extrudates were crushed using a laboratory mill to particles with a diameter less than 0.3 mm. A 0.7 g ground sample was suspended in 7 ml of distilled water at 20 °C in a tared centrifuge tube, stirred intermittently over a 10 min period. The resulting suspension was centrifuged at speeds 250 s-1 for 10 minutes in T24D type centri‐ fuge. The supernatant liquid was poured into a tared evaporating dish. The remaining gel was weighted and the WAI was calculated as WAI = wg/ws(%), where wg is a weight of gel

and ws is the weight of dry sample. Measurements were performed in 6 replications.

Water solubility index was determined from the amount of dried solids recovered during evaporation of supernatant obtained from the WAI analysis according to the method of Harper (1981). Results were calculated from formula WSI = wds/ws (%), where wds is the weight of dry solids of supernatant and ws is the weight of dry sample. Measurements were

The data reported was subjected to analysis of variance (ANOVA) by Duncan's test (P<0.05)

Specific mechanical energy during potato starch extrusion-cooking depends on the process parameters. The research revealed that the values of SME were within a range 298.8-990 kJkg-1 (0.083-0.275 kWhkg-1). These values were lower than the values obtained by Della Valle et al. (1995). The lowest energy consumption was observed during the extrusion-cook‐ ing process of potato starch at 140 °C. The highest energy consumption was recorded during the extrusion-cooking process at a temperature of 100 °C (at moisture content of 17 and 20%)

Studies have shown the energy consumption dependence from extruder screw speed (Fig. 10). Effect of moisture content on the SME was inconclusive. When carrying out the process at 100 °C, little change was observed (decrease) in specific mechanical energy. At higher temperature of extrusion it was observed that an increase in moisture content of starch in‐ creases the rate of the SME. It was most likely caused by increasing viscosity of processed slurry. Due to the presence of water the starch melts and underwent liquefaction, resulting

& Moscicki, 2009, Wolf, 2010).

330 Advances in Agrophysical Research

performed in 6 replications.

**4.2. Results and discussion**

and at 120 °C (moisture content 25 and 30%).

in lower glass transition temperature.

using SAS 9.1 software.

repetitions.

ish standard PN-A-79011-11:1998.

**Figure 11.** Degree of gelatinization of the potato starch extrusion-cooked at 100 °C

During our research has been noticed that the degree of potato starch gelatinization de‐ creased with increase of extrusion-cooking temperature and when processed starch con‐ tained more water (Fig. 11). That was evident especially when high rpm of the screw was used. The highest degree of gelatinization (96.5%) was recorded for starch extruded at 100 and 120 °C at the moisture content of 17%. The lowest degree of gelatinization (41%) was recorded for starch extruded at 140 °C at the moisture content of 30%. Such relatively low degree of gelatinization may happen due to relative short residence time of the dough in the extruder, which could stimulate the process. Nevertheless that has to be proved in more de‐ tailed measurements. Extrudates obtained under these conditions had properties of thermo‐ plastic starch.

tents Tp is much higher than 100 °C and, therefore, an increase of steam bubbles before

Extrusion-Cooking of Starch http://dx.doi.org/10.5772/52323 333

Native potato starch has WAI approximately 97% and WSI approximately 0.25%. The study showed that the baro-thermal modification of starch significantly affects on its water absorp‐

The research revealed that the value of WAI initially increased with increasing screw speed, and decreased at high speeds of extruder screw. With the increase in moisture content of processed potato starch the increase of water absorption was observed (Fig. 13). WAI values of the extruded potato starch ranged from 282 to 569% and generally did not deviate from

The highest values of water absorption were observed for starch extruded at 100 °C, the lowest for starch processed at 120 °C. It was connected with the progress of the degree of gelatinization. The increase in extrusion temperature to 140 °C caused a re-appreciation of WAI. Most likely due to lower glass transition temperature, the starch was more rapid melt‐ ing, and liquefaction, which could limit the degree of its degradation. Analysis of variance of the WAI, depending on the moisture content and screw speed, showed statistically signif‐ icant differences, with significance level of 0.05. Only for extrudates obtained at 140 °C there were no significant statistical differences in the relationship between water absorption and

The research showed that the value of the WSI increased with screw speed increase. The starch moisture content increase caused reduction of extruded starch solubility (Fig. 14). The

they end up collapsing, resulting in a high degree of expansion.

the values obtained for a typical starch extrudates (Mercier et al., 1998).

**Figure 13.** WAI of the potato starch extrusion-cooked at 100 °C

the screw speed.

tion and solubility in cold water.

**Figure 12.** Expansion index of the potato starch extrusion-cooked at 100 °C

Measurements of the expansion index of extruded potato starch showed that its value decreases with moisture content increase (Fig. 12). Extruder screw speed increase caused increase of expansion index. This is a common phenomenon for the most of the extru‐ dates. Extrudates were characterized by a typical structure, resembling a honeycomb structure. At high moisture contents of raw material (25 and 30%) the formation of "glassy" extrudates with a low degree of expansion was observed. This effect was partic‐ ularly visible for extrusion temperatures of 120 and 140 °C. Extrudates obtained under these conditions had homogeneous, amorphous structure without pores and steam bub‐ bles. Such behavior of the processed material is related to the glass transition tempera‐ ture (Tg) of starch and temperature of steam bubbles formation (Tp) (Della Valle et al., 1997, van Soest et al., 1996c). When the product temperature is higher than Tg and close to Tp, bubbles growth stops and the extrudate obtained its structure. At high moisture contents of raw material Tg and Tp may be lower than the temperature at which extru‐ date shrinkage begins as a result of condensation (about 100 °C). At low moisture con‐ tents Tp is much higher than 100 °C and, therefore, an increase of steam bubbles before they end up collapsing, resulting in a high degree of expansion.

Native potato starch has WAI approximately 97% and WSI approximately 0.25%. The study showed that the baro-thermal modification of starch significantly affects on its water absorp‐ tion and solubility in cold water.

The research revealed that the value of WAI initially increased with increasing screw speed, and decreased at high speeds of extruder screw. With the increase in moisture content of processed potato starch the increase of water absorption was observed (Fig. 13). WAI values of the extruded potato starch ranged from 282 to 569% and generally did not deviate from the values obtained for a typical starch extrudates (Mercier et al., 1998).

**Figure 13.** WAI of the potato starch extrusion-cooked at 100 °C

used. The highest degree of gelatinization (96.5%) was recorded for starch extruded at 100 and 120 °C at the moisture content of 17%. The lowest degree of gelatinization (41%) was recorded for starch extruded at 140 °C at the moisture content of 30%. Such relatively low degree of gelatinization may happen due to relative short residence time of the dough in the extruder, which could stimulate the process. Nevertheless that has to be proved in more de‐ tailed measurements. Extrudates obtained under these conditions had properties of thermo‐

**Figure 12.** Expansion index of the potato starch extrusion-cooked at 100 °C

Measurements of the expansion index of extruded potato starch showed that its value decreases with moisture content increase (Fig. 12). Extruder screw speed increase caused increase of expansion index. This is a common phenomenon for the most of the extru‐ dates. Extrudates were characterized by a typical structure, resembling a honeycomb structure. At high moisture contents of raw material (25 and 30%) the formation of "glassy" extrudates with a low degree of expansion was observed. This effect was partic‐ ularly visible for extrusion temperatures of 120 and 140 °C. Extrudates obtained under these conditions had homogeneous, amorphous structure without pores and steam bub‐ bles. Such behavior of the processed material is related to the glass transition tempera‐ ture (Tg) of starch and temperature of steam bubbles formation (Tp) (Della Valle et al., 1997, van Soest et al., 1996c). When the product temperature is higher than Tg and close to Tp, bubbles growth stops and the extrudate obtained its structure. At high moisture contents of raw material Tg and Tp may be lower than the temperature at which extru‐ date shrinkage begins as a result of condensation (about 100 °C). At low moisture con‐

plastic starch.

332 Advances in Agrophysical Research

The highest values of water absorption were observed for starch extruded at 100 °C, the lowest for starch processed at 120 °C. It was connected with the progress of the degree of gelatinization. The increase in extrusion temperature to 140 °C caused a re-appreciation of WAI. Most likely due to lower glass transition temperature, the starch was more rapid melt‐ ing, and liquefaction, which could limit the degree of its degradation. Analysis of variance of the WAI, depending on the moisture content and screw speed, showed statistically signif‐ icant differences, with significance level of 0.05. Only for extrudates obtained at 140 °C there were no significant statistical differences in the relationship between water absorption and the screw speed.

The research showed that the value of the WSI increased with screw speed increase. The starch moisture content increase caused reduction of extruded starch solubility (Fig. 14). The highest values of solubility (40%) were obtained for the modified starch at 120 °C. Process temperature growth caused an initial increase (120 °C) and than decrease (140 °C) in starch WSI. The changes of the solubility of starch were related with changes in the process of ge‐ latinization and starch degradation due to starch moisture content increase. At low to inter‐ mediate moisture content and high temperature, the water contained in starch might behave like a lubricant (Igura et al., 2001). Degradation of starch progressed by increasing extruder screw speed at low moisture content because less lubricant (water) was available. Analysis of variance of the WSI, depending on the moisture content and screw speed, showed statisti‐ cally significant differences, with significance level of 0.05.

scale researches to increase amount of starch in starch-plastic composites to the highest possible level. The final objective of these investigations is to obtain commercial items for one-time use, produced from pure starch and to exclude synthetic polymers from the formulation. Thermoplastic starch (TPS) seems to be a perfect solution because it can be processed with conventional technologies used in synthetic plastic manufacture (extru‐

Extrusion-Cooking of Starch http://dx.doi.org/10.5772/52323 335

To obtain thermoplastic starch, thermal and mechanical processing should disrupt semi crystalline starch granules. As the melting temperature of pure starch is substantially higher than its decomposition temperature there is a necessity to use plasticizers, for example wa‐ ter. Under the influence of temperature and shear forces, disruption of the natural crystal‐ line structure of starch granules and polysaccharides form a continuous polymer phase is reported. TPS produced from starch plastified only with water becomes very brittle at room temperature. To increase material flexibility and improve processing other plasticizers are also used, e.g. glycerol, propylene glycol, glucose, sorbitol and others. To improve the me‐ chanical properties of TPS based materials also other additives can be applied, like emulsifi‐

The blends of a potato starch Superior type, produced by AVEBE Company (NL), a glycerol (98,5% purity) produced by Polfa Odczynniki (PL) and cut flax fibres supplied by Polish producer BELKO Ltd Co., were used as a basic material during processing. The raw materi‐ als were mixed in a ribbon blender; a glycerol content varied from 18 to 30 wt % blend mass, and the fibres from 5% to 10% at the selected blends. After mixing the bland samples were packed in airtight plastic bags and stored for 24 hrs to intensify glycerol penetration into

Production of thermoplastic starch (TPS) was made in two steps. In first step starch, glycerol and flax fibre blends were extruded in a twin-screw extruder PASQUETTI, an Italian design, characterized by L/D = 5, and the screws diameter - 45mm. The extruder's die was fitted with a bronze matrix having one hole of the diameter ϕ = 3 mm. Thermoplastic starch was made with the screw's speed of 1,5 s-1. The temperature of extrusion in particular barrel parts and a die were between 80 °C and 140 °C; pressure in the die fluctuated between 10 MPa and 18 MPa. The product was cut by high-speed knife, which helped obtain pellets of

In the second step, the TPS pellets were processed on the injection moulding machine AR‐ BURG 220H90-350, L/D = 20,5. The injection speed was maintained at the level of 0,07-0,09 ms-1, injection time - 3s, and the temperature of the processes reached from 100 °C to 180 °C. The samples of injection mouldings (Fig. 15) were used during further examination of me‐

starch grains. Immediately before the extrusion the blends were remixed.

sion, injection moulding).

**5.1. Materials and methods**

previously set small size (Oniszczuk, 2006).

chanical properties of mouldings (Oniszczuk, 2006).

*5.1.1. Injecting moulding*

ers, cellulose, plant fibres, bark, kaolin, pectin and others.

**Figure 14.** WSI of the potato starch extrusion-cooked at 100 °C

### **5. Thermoplastic starch**

The interest to use starch as a basis for packaging material originates to the 1970's when en‐ vironmental awareness increased drastically. Since then a steady development of new prod‐ ucts can be seen. The possibility to compete in price with traditional materials, like plastics, has always been indispensable for the general acceptance of these new materials.

Starch biodegrades to carbon dioxide and water in a relatively short time compared with most synthetic polymers. Considering some drawbacks of the existing technologies of bi‐ odegradable materials manufacture, in the recent years there have been started largescale researches to increase amount of starch in starch-plastic composites to the highest possible level. The final objective of these investigations is to obtain commercial items for one-time use, produced from pure starch and to exclude synthetic polymers from the formulation. Thermoplastic starch (TPS) seems to be a perfect solution because it can be processed with conventional technologies used in synthetic plastic manufacture (extru‐ sion, injection moulding).

To obtain thermoplastic starch, thermal and mechanical processing should disrupt semi crystalline starch granules. As the melting temperature of pure starch is substantially higher than its decomposition temperature there is a necessity to use plasticizers, for example wa‐ ter. Under the influence of temperature and shear forces, disruption of the natural crystal‐ line structure of starch granules and polysaccharides form a continuous polymer phase is reported. TPS produced from starch plastified only with water becomes very brittle at room temperature. To increase material flexibility and improve processing other plasticizers are also used, e.g. glycerol, propylene glycol, glucose, sorbitol and others. To improve the me‐ chanical properties of TPS based materials also other additives can be applied, like emulsifi‐ ers, cellulose, plant fibres, bark, kaolin, pectin and others.

#### **5.1. Materials and methods**

#### *5.1.1. Injecting moulding*

highest values of solubility (40%) were obtained for the modified starch at 120 °C. Process temperature growth caused an initial increase (120 °C) and than decrease (140 °C) in starch WSI. The changes of the solubility of starch were related with changes in the process of ge‐ latinization and starch degradation due to starch moisture content increase. At low to inter‐ mediate moisture content and high temperature, the water contained in starch might behave like a lubricant (Igura et al., 2001). Degradation of starch progressed by increasing extruder screw speed at low moisture content because less lubricant (water) was available. Analysis of variance of the WSI, depending on the moisture content and screw speed, showed statisti‐

The interest to use starch as a basis for packaging material originates to the 1970's when en‐ vironmental awareness increased drastically. Since then a steady development of new prod‐ ucts can be seen. The possibility to compete in price with traditional materials, like plastics,

Starch biodegrades to carbon dioxide and water in a relatively short time compared with most synthetic polymers. Considering some drawbacks of the existing technologies of bi‐ odegradable materials manufacture, in the recent years there have been started large-

has always been indispensable for the general acceptance of these new materials.

cally significant differences, with significance level of 0.05.

334 Advances in Agrophysical Research

**Figure 14.** WSI of the potato starch extrusion-cooked at 100 °C

**5. Thermoplastic starch**

The blends of a potato starch Superior type, produced by AVEBE Company (NL), a glycerol (98,5% purity) produced by Polfa Odczynniki (PL) and cut flax fibres supplied by Polish producer BELKO Ltd Co., were used as a basic material during processing. The raw materi‐ als were mixed in a ribbon blender; a glycerol content varied from 18 to 30 wt % blend mass, and the fibres from 5% to 10% at the selected blends. After mixing the bland samples were packed in airtight plastic bags and stored for 24 hrs to intensify glycerol penetration into starch grains. Immediately before the extrusion the blends were remixed.

Production of thermoplastic starch (TPS) was made in two steps. In first step starch, glycerol and flax fibre blends were extruded in a twin-screw extruder PASQUETTI, an Italian design, characterized by L/D = 5, and the screws diameter - 45mm. The extruder's die was fitted with a bronze matrix having one hole of the diameter ϕ = 3 mm. Thermoplastic starch was made with the screw's speed of 1,5 s-1. The temperature of extrusion in particular barrel parts and a die were between 80 °C and 140 °C; pressure in the die fluctuated between 10 MPa and 18 MPa. The product was cut by high-speed knife, which helped obtain pellets of previously set small size (Oniszczuk, 2006).

In the second step, the TPS pellets were processed on the injection moulding machine AR‐ BURG 220H90-350, L/D = 20,5. The injection speed was maintained at the level of 0,07-0,09 ms-1, injection time - 3s, and the temperature of the processes reached from 100 °C to 180 °C. The samples of injection mouldings (Fig. 15) were used during further examination of me‐ chanical properties of mouldings (Oniszczuk, 2006).

**Figure 15.** Samples of TPS mouldings

#### *5.1.2. Film blowing*

Similar procedure of the TPS granulates production was used to obtain half product for the film blowing. The basic materials were the blends of 2 main components: potato starch and a glycerol. Selected blends were enriched with the addition of the emulsifiers: polyoxyethy‐ lene sorbitan monolaurate (Tween 20) and glycerol monostearate at the amount up to 2%.

**Figure 16.** TPS film blowing

elongation during stretching (Oniszczuk, 2006).

at the maximum strength and tensile.

**5.2. Results and discussion**

The examination of the mechanical properties of TPS mouldings was performer on a univer‐ sal texture appliance Zwick type BDO-FBO0, 5TH equipped in the head 0,5kN. The travel speed of the head was 3 mmmin-1. The test focused on the maximum stress and maximum

Extrusion-Cooking of Starch http://dx.doi.org/10.5772/52323 337

The assessment of the original shrinkage of the biopolymer mouldings was done by means of the micrometer screw initiating the measurement 24 hours after producing the samples.

The tensile testing of film proceeded at the tester Zwick type Z2.5/TN1S using the standard tensile test ISO 527. There was applied the crosshead 1 kN, sample length 100 mm, sample width 17 mm, each sample thickness was measured with micrometer. The crosshead speed for initial stress was 10 mmmin-1, speed up to flexibility limit – 50 mmmin-1, test speed – 200 mmmin-1. The measurements were made on maximum strength, tensile strength, elongation

DSC technique has been used often to study the glass transition temperature of thermoplas‐ tic starch. The results differ from one another significantly (Shi et al., 2007, van Soest, 1996, Talja et al., 2007). In accordance to Yu & Christi (2001) some key factors, such as sample

The process of film extrusion with film blowing method was conducted on a line specially designed for film manufacture in the Department of Food Process Engineering, Lublin Uni‐ versity of Life Science (PL), based on a single screw plastic extruder of L/D=35 (see Fig. 16). That line was produced by SAVO Ltd Co., Poland. TPS film was produced using 2 screws of varied geometry (a compression ratio: 2,0 and 3,5), and the screw rotational speed ranged from 50 till 90 rpm. The film was extruded at the barrel and crossdie temperature ranging 70 – 155 °C.

#### *5.1.3. Measurement of physical properties*

The measurements of glass transition temperature Tg of thermoplastic starch were done with the use of the Differential Scanning Calorimetry on the Perkin Elmer DSC 7. The samples of thermoplastic starch 7 – 10 mg mass were heated from the temperature of 25 °C to 180 °C at 10 °Cmin-1 speed, and next cooled at the same rate down to 25 °C and fi‐ nally heated up to 180 °C. The thermal transitions were calculated from the second heat‐ ing cycle. To confirm the obtained results the tests were repeated in a DSC 2920 modulated DSC TA Instruments. The samples were heated from 0 °C up to 150 °C at the rate 1 °Cmin-1 and then cooled at the same rate to 0 °C (Mitrus, 2005b).

**Figure 16.** TPS film blowing

**Figure 15.** Samples of TPS mouldings

336 Advances in Agrophysical Research

*5.1.3. Measurement of physical properties*

Similar procedure of the TPS granulates production was used to obtain half product for the film blowing. The basic materials were the blends of 2 main components: potato starch and a glycerol. Selected blends were enriched with the addition of the emulsifiers: polyoxyethy‐ lene sorbitan monolaurate (Tween 20) and glycerol monostearate at the amount up to 2%.

The process of film extrusion with film blowing method was conducted on a line specially designed for film manufacture in the Department of Food Process Engineering, Lublin Uni‐ versity of Life Science (PL), based on a single screw plastic extruder of L/D=35 (see Fig. 16). That line was produced by SAVO Ltd Co., Poland. TPS film was produced using 2 screws of varied geometry (a compression ratio: 2,0 and 3,5), and the screw rotational speed ranged from 50 till 90 rpm. The film was extruded at the barrel and crossdie temperature ranging 70

The measurements of glass transition temperature Tg of thermoplastic starch were done with the use of the Differential Scanning Calorimetry on the Perkin Elmer DSC 7. The samples of thermoplastic starch 7 – 10 mg mass were heated from the temperature of 25 °C to 180 °C at 10 °Cmin-1 speed, and next cooled at the same rate down to 25 °C and fi‐ nally heated up to 180 °C. The thermal transitions were calculated from the second heat‐ ing cycle. To confirm the obtained results the tests were repeated in a DSC 2920 modulated DSC TA Instruments. The samples were heated from 0 °C up to 150 °C at the

rate 1 °Cmin-1 and then cooled at the same rate to 0 °C (Mitrus, 2005b).

*5.1.2. Film blowing*

– 155 °C.

The examination of the mechanical properties of TPS mouldings was performer on a univer‐ sal texture appliance Zwick type BDO-FBO0, 5TH equipped in the head 0,5kN. The travel speed of the head was 3 mmmin-1. The test focused on the maximum stress and maximum elongation during stretching (Oniszczuk, 2006).

The assessment of the original shrinkage of the biopolymer mouldings was done by means of the micrometer screw initiating the measurement 24 hours after producing the samples.

The tensile testing of film proceeded at the tester Zwick type Z2.5/TN1S using the standard tensile test ISO 527. There was applied the crosshead 1 kN, sample length 100 mm, sample width 17 mm, each sample thickness was measured with micrometer. The crosshead speed for initial stress was 10 mmmin-1, speed up to flexibility limit – 50 mmmin-1, test speed – 200 mmmin-1. The measurements were made on maximum strength, tensile strength, elongation at the maximum strength and tensile.

#### **5.2. Results and discussion**

DSC technique has been used often to study the glass transition temperature of thermoplas‐ tic starch. The results differ from one another significantly (Shi et al., 2007, van Soest, 1996, Talja et al., 2007). In accordance to Yu & Christi (2001) some key factors, such as sample preparation, type of pan and measurements conditions, have an affect on the results of ther‐ mal behavior of starch as measured by DSC. The tests show that both, amylose and amylo‐ pectin had a higher Tg`s in absence of glycerol. The estimates demonstrated that the Tg of dry amylose and amylopctin is 227 °C, while Bizot et al. (1997) assessed the dry starch Tg – 332 °C. What's more, to lower the Tg of potato starch closer to the ambient temperature 0,21 g of water should be used for 1g of starch (Bizot et al., 1997, Myllarinen et al., 2002). Myllari‐ nen et al. (2002) confirmed that the Tg of amylose and amylopectin can be equal to the ambi‐ ent temperature when the water content is 21%, however at the same glycerol level the Tg can be still as high as 93 °C. It can be concluded that glycerol is a less effective plasticizer than water. On the basis of computations they claim that in order to lower a Tg value to the ambient temperature 35% glycerol should be applied.

temperature of 120 °C. On the basis of the performed examination, it can be stated that the addition of flax fibres positively influenced the mechanical properties of biopolymer mould‐ ings. It was noted that together with the percentage growth of the fibres content the me‐ chanical strength of samples was improved. The samples with 20% of glycerol content and 10 % of flax fibres were of the highest strength (26,5 MPa). In the case of mouldings obtained from granulate containing 22% of glycerol, the addition of 5% and 10% of fibres slightly in‐ fluenced the improvement in strength. It was noted that together with the growth of the glycerol content in mouldings containing flax fibres their mechanical strength dropped. Glycerol acts like diluent and weakens the intermolecular bonds between flax fibres and starch. The lowest mechanical strength was observed with mouldings produced from gran‐ ulates containing 25% of glycerol. The same tendency was registered in the case of samples obtained at different production temperatures the highest mechanical strength was dis‐ played by mouldings produced at the material injection temperature of 140 °C (maximal stress 27,8 MPa), and the the lowest mechanical strength was noticed for mouldings ob‐

Extrusion-Cooking of Starch http://dx.doi.org/10.5772/52323 339

**Figure 18.** Relationship between the maximal stress and the fibre content in samples (sample injection temperature

Another important parameter is the maximal elongation of the samples during stretching. For TPS without fibres added, it can be stated that for the full spectrum of injection tempera‐ tures and for all glycerol concentrations investigated the maximal elongation coincides with increasing injection temperature and with the increase of the glycerol content of the sample. The addition of fibres affected the elongational behaviour of the material considerably.

During the research it was noticed that the maximal elongation values coincided with the growing temperature of material injection and with the increase of the glycerol con‐ tent in the sample. The largest maximal elongation (58,5%) was recorded at the level of 25% of glycerol content in mouldings and the material injection temperature of 180 °C. The lowest maximal elongation of 10% was recorded with mouldings having 20% of

tained at the temperature of 180 °C (10,8 MPa).

120 °C)

The glass temperature measurements revealed that with glycerol content growth in mate‐ rial blend, the Tg of the obtained material decreases almost linearly. The highest ob‐ served Tg was 132 °C for 15% glycerol, the lowest was 18 °C at a glycerol level of 30%. Figure 17 shows the changes of the glass transition temperature with changing glycerol content. The moisture content of all the mixtures was 15%. This results are similar to this obtained by Graff et al. (2003).

**Figure 17.** Influence of the glycerol content on the Tg of thermoplastic starch

The mechanical properties of biocomposites depend on a number of factors. These are the quantity and type of fibre added to the material, but also type and amount of plasticizers, finally - the production temperature plays also important role. A predominant influence on the mechanical properties of biocomposites have both: natural fibres and plasticizer. During our investigations it has been observed that the addition of fibres enhances the mechanical strength of mouldings samples. The addition of extra plasticizer causes the decline in its maximum stress.

Figure 18 shows the relationship between the maximal stress and the content of flax fibres in the samples containing 20, 22 and 25% of glycerol and produced at the material injection temperature of 120 °C. On the basis of the performed examination, it can be stated that the addition of flax fibres positively influenced the mechanical properties of biopolymer mould‐ ings. It was noted that together with the percentage growth of the fibres content the me‐ chanical strength of samples was improved. The samples with 20% of glycerol content and 10 % of flax fibres were of the highest strength (26,5 MPa). In the case of mouldings obtained from granulate containing 22% of glycerol, the addition of 5% and 10% of fibres slightly in‐ fluenced the improvement in strength. It was noted that together with the growth of the glycerol content in mouldings containing flax fibres their mechanical strength dropped. Glycerol acts like diluent and weakens the intermolecular bonds between flax fibres and starch. The lowest mechanical strength was observed with mouldings produced from gran‐ ulates containing 25% of glycerol. The same tendency was registered in the case of samples obtained at different production temperatures the highest mechanical strength was dis‐ played by mouldings produced at the material injection temperature of 140 °C (maximal stress 27,8 MPa), and the the lowest mechanical strength was noticed for mouldings ob‐ tained at the temperature of 180 °C (10,8 MPa).

preparation, type of pan and measurements conditions, have an affect on the results of ther‐ mal behavior of starch as measured by DSC. The tests show that both, amylose and amylo‐ pectin had a higher Tg`s in absence of glycerol. The estimates demonstrated that the Tg of dry amylose and amylopctin is 227 °C, while Bizot et al. (1997) assessed the dry starch Tg – 332 °C. What's more, to lower the Tg of potato starch closer to the ambient temperature 0,21 g of water should be used for 1g of starch (Bizot et al., 1997, Myllarinen et al., 2002). Myllari‐ nen et al. (2002) confirmed that the Tg of amylose and amylopectin can be equal to the ambi‐ ent temperature when the water content is 21%, however at the same glycerol level the Tg can be still as high as 93 °C. It can be concluded that glycerol is a less effective plasticizer than water. On the basis of computations they claim that in order to lower a Tg value to the

The glass temperature measurements revealed that with glycerol content growth in mate‐ rial blend, the Tg of the obtained material decreases almost linearly. The highest ob‐ served Tg was 132 °C for 15% glycerol, the lowest was 18 °C at a glycerol level of 30%. Figure 17 shows the changes of the glass transition temperature with changing glycerol content. The moisture content of all the mixtures was 15%. This results are similar to this

The mechanical properties of biocomposites depend on a number of factors. These are the quantity and type of fibre added to the material, but also type and amount of plasticizers, finally - the production temperature plays also important role. A predominant influence on the mechanical properties of biocomposites have both: natural fibres and plasticizer. During our investigations it has been observed that the addition of fibres enhances the mechanical strength of mouldings samples. The addition of extra plasticizer causes the decline in its

Figure 18 shows the relationship between the maximal stress and the content of flax fibres in the samples containing 20, 22 and 25% of glycerol and produced at the material injection

ambient temperature 35% glycerol should be applied.

**Figure 17.** Influence of the glycerol content on the Tg of thermoplastic starch

obtained by Graff et al. (2003).

338 Advances in Agrophysical Research

maximum stress.

**Figure 18.** Relationship between the maximal stress and the fibre content in samples (sample injection temperature 120 °C)

Another important parameter is the maximal elongation of the samples during stretching. For TPS without fibres added, it can be stated that for the full spectrum of injection tempera‐ tures and for all glycerol concentrations investigated the maximal elongation coincides with increasing injection temperature and with the increase of the glycerol content of the sample. The addition of fibres affected the elongational behaviour of the material considerably.

During the research it was noticed that the maximal elongation values coincided with the growing temperature of material injection and with the increase of the glycerol con‐ tent in the sample. The largest maximal elongation (58,5%) was recorded at the level of 25% of glycerol content in mouldings and the material injection temperature of 180 °C. The lowest maximal elongation of 10% was recorded with mouldings having 20% of glycerol. To conclude, it corroborates the positive influence of plasticizer on the improve‐ ment of moulding flexibility.

When examining the shrinkage of mouldings produced with 25% of glycerol share, consid‐ erable differences. After 24 h from producing mouldings, the shrinkage level was almost 11,7% in samples without fibres, 1,75% when applying 5% of flax fibres and 0,67% when 10% of fibres were added. For mouldings obtained with 20% of glycerol content, the shrink‐ age values were lower and least dependent on the addition of fibres. The shrinkage values for these trials did not exceed 1,5%, which indicates a significant stability of the material ob‐ tained in specific production conditions. The original shrinkage of mouldings without the addition of fibres was high and amounted to about 6% when using 22% of glycerol and about 12% with 25% of plasticizer. This indicates a stabilizing role of fibres, which main‐ tained the original moulding structure in an almost unchanged shape. It is a very desirable feature when it comes to keeping the shape of ready packaging if produced from such bio‐

Extrusion-Cooking of Starch http://dx.doi.org/10.5772/52323 341

**Figure 20.** Influence of flax fibres content and glycerol content on the size of original shrinkage of (measured after 24

The tests of the film extrusion showed that the best results were recorded for the starch mix‐ tures with 20-25% glycerol. At processing temperature below 120 °C the material was not fully processed and some granulate residuals appeared at the film surface. The obtained films were thick, opaque and semi-transparent, that after some time lost flexibility and got brittle due to their drying up. When the higher pressing temperatures were applied as well as a screw with a mixer arm, films of good quality were obtained. They were flexible semitransparent films readily put to the blow moulding. Unfortunately because of the crosshead

polymers.

h); injection temperature 120 °C

Addition of flax fibres influenced the drop of the maximal elongation of biopolymer mould‐ ings. The growth of the percentage share of fibres in the mixture worked upon the decrease of the flexibility of samples during the tension test (Fig. 19).

**Figure 19.** Relationship between the maximal elongation and the flax fibre content in samples (injection temperature 180 °C).

With the application of the production temperature of 180 °C, the largest maximal elonga‐ tion (17,1%) was observed with the samples containing 25% of glycerol and 5% of flax fibres. The lowest maximal elongation (3%) was observed with mouldings produced from granu‐ late containing 20% of glycerol and 10% of flax fibres. In the case of mouldings produced at the injection temperature of 120 °C, the addition of fibres barely influenced the reduction of the maximum elongation and amounted to 10,5% for mouldings containing 5% of flax fibres and 9,7% for mouldings of double fibre content. It proves the negative impact of fibres on the flexibility of biopolymer mouldings containing such material.

Besides the improvement of durability, the fibres used for the mouldings manufacture stabi‐ lize the shape and decrease the original shrinkage of ready products. Oniszczuk & Janssen (2009) describes that an increased linen fibre content is decreased the values for original shrink. The addition of plasticizer (glycerol) had an adverse effect on the original shrinkage.

The examination of original shrinkage of biopolymer mouldings showed that in the whole range of temperatures of sample production (100 °C, 120 °C, 140 °C, 160 °C and 180 °C) and after the time of shrinkage measurement (measured after 24 h) a similar tendency was ob‐ served. Together with the increase of the share of flax fibres, the value of the original shrink‐ age was dropping, regardless of the time when measurement of the shrinkage was made. However, together with the growth of the share of glycerol, the value of the original shrink‐ age of mouldings slightly increased (Fig. 20).

When examining the shrinkage of mouldings produced with 25% of glycerol share, consid‐ erable differences. After 24 h from producing mouldings, the shrinkage level was almost 11,7% in samples without fibres, 1,75% when applying 5% of flax fibres and 0,67% when 10% of fibres were added. For mouldings obtained with 20% of glycerol content, the shrink‐ age values were lower and least dependent on the addition of fibres. The shrinkage values for these trials did not exceed 1,5%, which indicates a significant stability of the material ob‐ tained in specific production conditions. The original shrinkage of mouldings without the addition of fibres was high and amounted to about 6% when using 22% of glycerol and about 12% with 25% of plasticizer. This indicates a stabilizing role of fibres, which main‐ tained the original moulding structure in an almost unchanged shape. It is a very desirable feature when it comes to keeping the shape of ready packaging if produced from such bio‐ polymers.

glycerol. To conclude, it corroborates the positive influence of plasticizer on the improve‐

Addition of flax fibres influenced the drop of the maximal elongation of biopolymer mould‐ ings. The growth of the percentage share of fibres in the mixture worked upon the decrease

**Figure 19.** Relationship between the maximal elongation and the flax fibre content in samples (injection temperature

With the application of the production temperature of 180 °C, the largest maximal elonga‐ tion (17,1%) was observed with the samples containing 25% of glycerol and 5% of flax fibres. The lowest maximal elongation (3%) was observed with mouldings produced from granu‐ late containing 20% of glycerol and 10% of flax fibres. In the case of mouldings produced at the injection temperature of 120 °C, the addition of fibres barely influenced the reduction of the maximum elongation and amounted to 10,5% for mouldings containing 5% of flax fibres and 9,7% for mouldings of double fibre content. It proves the negative impact of fibres on

Besides the improvement of durability, the fibres used for the mouldings manufacture stabi‐ lize the shape and decrease the original shrinkage of ready products. Oniszczuk & Janssen (2009) describes that an increased linen fibre content is decreased the values for original shrink. The addition of plasticizer (glycerol) had an adverse effect on the original shrinkage.

The examination of original shrinkage of biopolymer mouldings showed that in the whole range of temperatures of sample production (100 °C, 120 °C, 140 °C, 160 °C and 180 °C) and after the time of shrinkage measurement (measured after 24 h) a similar tendency was ob‐ served. Together with the increase of the share of flax fibres, the value of the original shrink‐ age was dropping, regardless of the time when measurement of the shrinkage was made. However, together with the growth of the share of glycerol, the value of the original shrink‐

the flexibility of biopolymer mouldings containing such material.

age of mouldings slightly increased (Fig. 20).

ment of moulding flexibility.

340 Advances in Agrophysical Research

180 °C).

of the flexibility of samples during the tension test (Fig. 19).

**Figure 20.** Influence of flax fibres content and glycerol content on the size of original shrinkage of (measured after 24 h); injection temperature 120 °C

The tests of the film extrusion showed that the best results were recorded for the starch mix‐ tures with 20-25% glycerol. At processing temperature below 120 °C the material was not fully processed and some granulate residuals appeared at the film surface. The obtained films were thick, opaque and semi-transparent, that after some time lost flexibility and got brittle due to their drying up. When the higher pressing temperatures were applied as well as a screw with a mixer arm, films of good quality were obtained. They were flexible semitransparent films readily put to the blow moulding. Unfortunately because of the crosshead with 1mm slit application and a low powered compressor the resulting film had minimum thickness 120μm, yet the production of much more thinner ones is possible.

The extrusion process of starch increased the water absorption and cold water solubility. These changes are closely related to the course of the process of starch gelatinization; degra‐

Extrusion-Cooking of Starch http://dx.doi.org/10.5772/52323 343

Modification of starch by extrusion-cooking technique is characterized by relatively low spe‐ cific mechanical energy consumption. SME values were within a range from 298.8 to 990 kJkg-1. Significant impact on the values of the SME had a screw speed, very little impact had

When the glycerol content in TPS increases from 15 to 30% the glass transition temperature

The performed examination of TPS injection moulding showed that it's possible to produce shaped biodegradable packaging materials. The addition of flax fibres to raw material mix‐ ture positively influenced the improvement of the mechanical strength of mouldings in the entire range of glycerol addition to mixtures (mouldings produced from the granulate con‐

The increased glycerol content in the material and the growth of injection temperature re‐ sulted in better elasticity of mouldings. Its drop was caused by the presence of fibres in

The increase of the percentage share of glycerol in the mixture visibly contributed to the growth of the value of the original shrinkage of mouldings. The lowest values of the original shrinkage of samples were observed at the material injection temperature of 180 °C. The ad‐ dition of flax fibres to mouldings in the entire range of their production temperatures posi‐

The most advantageous strength properties were recorded for the films with 20 – 25% glyc‐ erol. Polyoxyethylene sorbitan monolaurate (Tween 20) and glycerol monostearate in amount up to 2% have substantially improved (even by over 50%) film tensile susceptibility. The analysis of the mechanical properties measurements of TPS films proved that the extru‐ sion processing parameters, emulsifier presence and water content in material exert a vital impact on film strength and elongation. The use of screw of 3,5 compression ratio equipped with extra mixing section affected film strength more, while a screw of 2,0 compression ratio influenced film elongation in a greater measure. According to the expectations, the applica‐ tion of the screw of higher compression ratio increases energy-consumption during extru‐

Department of Food Process Engineering, Lublin University of Life Sciences, Lublin, Poland

dation and their extent depends on the extrusion parameters used

decreases almost linearly from 132 to 18 °C at moisture contents 15%.

taining 10% of flax fibres exhibited the greatest mechanical strength).

tively influences the stability of shape and the reduction of shrinkage.

L. Moscicki, M. Mitrus, A. Wojtowicz, T. Oniszczuk and A. Rejak

\*Address all correspondence to: leszek.moscicki@up.lublin.pl

a moisture content of raw material.

granulate.

sion processing.

**Author details**

**Figure 21.** Example of the tests results of the TPS film strength

The addition of the emulsifiers: polyoxyethylene sorbitan monolaurate (Tween 20) and glyc‐ erol monostearate at the amount up to 2% has considerably improved film flexibility. More‐ over, it was found that mixture damped up with only some water (2-5%) induced an increase of film flexibility and strength. Example of the tests results of the TPS film strength is shown on figure 21.

The analysis of the mechanical properties measurements of TPS films proved that the extru‐ sion processing parameters, emulsifier presence and water content in the material exert a vi‐ tal impact on film strength and its elongation. The use of the screw of 3,5 compression ratio, equipped with an extra mixing section affected film strength more, while a screw of 2,0 com‐ pression ratio influenced the film elongation in a greater measure. According to the expecta‐ tions, the application of the screw of 3,5c.r. resulted in higher energy-consumption during extrusion processing.

## **6. Conclusive remarks**

Extrusion-cooking technique allows creating the degree of gelatinization of processed starch. It is possible to achieve low or high level of gelatinization depending on the process parameters. This is especially important for food and feed applications.

Expansion index of starchy extrudates largely depends on the parameters of the extrusion process. Its value decreased with moisture content increase while increased with screw speed increase.

The extrusion process of starch increased the water absorption and cold water solubility. These changes are closely related to the course of the process of starch gelatinization; degra‐ dation and their extent depends on the extrusion parameters used

Modification of starch by extrusion-cooking technique is characterized by relatively low spe‐ cific mechanical energy consumption. SME values were within a range from 298.8 to 990 kJkg-1. Significant impact on the values of the SME had a screw speed, very little impact had a moisture content of raw material.

When the glycerol content in TPS increases from 15 to 30% the glass transition temperature decreases almost linearly from 132 to 18 °C at moisture contents 15%.

The performed examination of TPS injection moulding showed that it's possible to produce shaped biodegradable packaging materials. The addition of flax fibres to raw material mix‐ ture positively influenced the improvement of the mechanical strength of mouldings in the entire range of glycerol addition to mixtures (mouldings produced from the granulate con‐ taining 10% of flax fibres exhibited the greatest mechanical strength).

The increased glycerol content in the material and the growth of injection temperature re‐ sulted in better elasticity of mouldings. Its drop was caused by the presence of fibres in granulate.

The increase of the percentage share of glycerol in the mixture visibly contributed to the growth of the value of the original shrinkage of mouldings. The lowest values of the original shrinkage of samples were observed at the material injection temperature of 180 °C. The ad‐ dition of flax fibres to mouldings in the entire range of their production temperatures posi‐ tively influences the stability of shape and the reduction of shrinkage.

The most advantageous strength properties were recorded for the films with 20 – 25% glyc‐ erol. Polyoxyethylene sorbitan monolaurate (Tween 20) and glycerol monostearate in amount up to 2% have substantially improved (even by over 50%) film tensile susceptibility. The analysis of the mechanical properties measurements of TPS films proved that the extru‐ sion processing parameters, emulsifier presence and water content in material exert a vital impact on film strength and elongation. The use of screw of 3,5 compression ratio equipped with extra mixing section affected film strength more, while a screw of 2,0 compression ratio influenced film elongation in a greater measure. According to the expectations, the applica‐ tion of the screw of higher compression ratio increases energy-consumption during extru‐ sion processing.

## **Author details**

with 1mm slit application and a low powered compressor the resulting film had minimum

The addition of the emulsifiers: polyoxyethylene sorbitan monolaurate (Tween 20) and glyc‐ erol monostearate at the amount up to 2% has considerably improved film flexibility. More‐ over, it was found that mixture damped up with only some water (2-5%) induced an increase of film flexibility and strength. Example of the tests results of the TPS film strength

The analysis of the mechanical properties measurements of TPS films proved that the extru‐ sion processing parameters, emulsifier presence and water content in the material exert a vi‐ tal impact on film strength and its elongation. The use of the screw of 3,5 compression ratio, equipped with an extra mixing section affected film strength more, while a screw of 2,0 com‐ pression ratio influenced the film elongation in a greater measure. According to the expecta‐ tions, the application of the screw of 3,5c.r. resulted in higher energy-consumption during

Extrusion-cooking technique allows creating the degree of gelatinization of processed starch. It is possible to achieve low or high level of gelatinization depending on the process

Expansion index of starchy extrudates largely depends on the parameters of the extrusion process. Its value decreased with moisture content increase while increased with screw

parameters. This is especially important for food and feed applications.

thickness 120μm, yet the production of much more thinner ones is possible.

**Figure 21.** Example of the tests results of the TPS film strength

is shown on figure 21.

342 Advances in Agrophysical Research

extrusion processing.

speed increase.

**6. Conclusive remarks**

L. Moscicki, M. Mitrus, A. Wojtowicz, T. Oniszczuk and A. Rejak

\*Address all correspondence to: leszek.moscicki@up.lublin.pl

Department of Food Process Engineering, Lublin University of Life Sciences, Lublin, Poland

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**Chapter 14**

**Determination of Food Quality by Using Spectroscopic**

Food is a complex system comprised predominantly of water, fat, proteins and carbohy‐ drates together with numerous minor components. The functional properties of these com‐ ponents, which are governed by their molecular structure and intra- and intermolecular interactions within food system, and the amounts present define the characteristics of food products. Quality of food products refers to the minimum standards for substances to quali‐ fy as fit for human consumption or permitted to come in contact with food. Appearance, col‐ or, flavor and texture are critical aspects for the sensory quality of food. The food quality includes also chemical, biological and microbial factors, e.g. instability of food products, which limits their shelf life and is connected with irreversible chemical and enzymatic reac‐ tions [1]. Recently, public interest in food quality and production has increased, probably re‐ lated to changes in eating habits, consumer behavior, and the development and increased industrialization of the food supplying chains. The demand for high quality and safety in food production obviously calls for high standards for quality and process control, which in

Spectroscopic methods have been historically very successful at evaluating the quality of ag‐ ricultural products, especially food. These methods are highly desirable for analysis of food components because they often require minimal or no sample preparation, provide rapid and on-line analysis, and have the potential to run multiple tests on a single sample. These advantages particularly apply to nuclear magnetic resonance (NMR), infrared (IR), and near-infrared (NIR) spectroscopy. The latter technique is routinely used as a quality assur‐ ance tool to determine compositional and functional analysis of food ingredients, process in‐ termediates, and finished products [1]. Additionally, UV–VIS spectroscopy, fluorescence and mid-infrared (MIR) and Raman spectroscopy are used in the food quality monitoring.

> © 2013 Nawrocka and Lamorska; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2013 Nawrocka and Lamorska; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

**Methods**

**1. Introduction**

http://dx.doi.org/10.5772/52722

Agnieszka Nawrocka and Joanna Lamorska

Additional information is available at the end of the chapter

turns requires appropriate analytical tools to investigate food.

