**3. Effects of ionizing radiation on functional properties**

The physicochemical and functional properties of starch in various applications are of great interest, especially for manufacturers of starch-based products. Aspects related to the ionizing radiation effects on physical, chemical, and functional characteristics of starch are onward presented.

### **3.1. Physicochemical properties**

**2.2. Radiation quantities**

56 Applications of Modified Starches

point in the region of interest [29]:

where *dε*

*D* = \_\_\_ *<sup>d</sup><sup>ε</sup>*

*D*̇ = \_\_\_ *dD*

The SI derived unit of absorbed dose rate is the *Gy/s*.

and irradiation dose rate, respectively.

Gamma rays -Cold method

Electron beam -Cold method

absorbed dose, the *rad* that is still tolerated, but less used:

1 Gy = 1 J/kg = 100 rad

**2.3. Advantages and disadvantages of ionizing radiation processing**

**Type of radiation Advantages Disadvantages**

accompanied by some disadvantages as shown in **Table 2**.


**Table 2.** Ionizing radiation processing: Advantages and disadvantages.



and d*m* is the mass of that volume element.

The most used dosimetric quantities and their units are the absorbed dose and the absorbed dose rate according to the International Commission on Radiation Units and Measurements (ICRU) Report no. 33 [28]. Moreover, these radiation quantities are the most important in the physical quantities used in the dosimetry field in order to optimize and control the irradiation process [29, 30].

The *absorbed dose*, *D*, is the amount of energy absorbed per unit mass of irradiated matter at a

The SI derived unit of absorbed dose is the *gray* (Gy), which replaced the earlier unit of

For this absorbed dose, the rate of change of it with time can be defined as the absorbed dose rate, *D*̇

The absorbed dose and the absorbed dose rate will be hereinafter referred as irradiation dose

Ionizing radiation has many advantages in material processing, being an effective tool to induce changes in structure and functional properties of materials without environmental negative implication. Thus, it is an environmentally friendly process that involves no use of polluting agents, no generation of undesirable residual products, and no penetration of toxic substances in treated products. Despite the advantages, ionizing radiation processing is

¯

¯ is the mean energy imparted by ionizing radiation to the matter in a volume element

*dm* (1)

*dt* (2)




:

The moisture contents of starches extracted from various botanical sources (lotus, sago, tapioca, wheat) were insignificantly affected by gamma radiation up to 20 kGy (dose rate ≤ 9 kGy/h) and electron beam up to 30 kGy [13, 23]. On the other hand, the moisture contents of rice starches were also insignificantly affected by gamma radiation at low doses (<1.5 kGy with dose rate of 0.63 kGy/h) [31], whereas a significant reduction in moisture content occurred at irradiation doses >2 kGy (dose rate of 0.4 kGy/h) as a result of radiation energy dissipation while ionizing radiation penetrates the starch sample [15]. Also, for starch extracted from elephant foot yam, the amount of moisture decreased significantly by gamma irradiation up to 25 kGy with dose rate of 2 kGy/h [19]. According to Reddy et al. [19], the reduction in the moisture content of starch sample by radiation processing may improve the shelf life of starch by avoiding the microorganisms' development.

pH of aqueous starch solutions decreased with increase of irradiation dose regardless of the botanical origin of the starch [5, 14, 16, 19, 23, 31–33]. The descending change of solution pH after irradiation could be attributed to the formation of chemical groups with acidic character such as carboxyl, carbonyl, or peroxide groups. Moreover, this behavior is sustained due to the fact that radiation processing of starch was generally performed in the presence of oxygen, thus promoting the appearance of free radicals, compounds with carbonyl bonds (aldehydes/ketones), organic peroxides, or other polysaccharide degradation products [34] that can lead to the increase of starch acidity. Therefore, the reduction of solution pH is strongly correlated with the increase of carboxyl content by the ionizing radiation processing of starch.

The water solubility can be improved concomitantly with the reduction of swelling power of granule by ionizing radiation processing for all starches. Therefore, the solubility value increased with the increase of irradiation dose for starches extracted from various botanical sources (corn, wheat, rice, potato, bean, elephant foot yam, lotus, chickpea, and Indian horse chestnut) [5, 9, 10, 15, 16, 18, 19, 21–23, 31–33, 35, 36]. The increase in solubility was due to the increase in polarity as a result of chain scission under irradiation and the decrease in inter-chain hydrogen bonds [35]. Such behavior demonstrates clearly that the starch molecules suffered important changes as a consequence of a degradation phenomenon induced by ionizing radiation processing.

The ionizing radiation processing of all types of starches caused the reduction of **swelling power** as the increase of the irradiation dose, especially at higher doses [5, 9, 10, 15–17, 19, 21, 22, 31, 32, 36–38]. This evolution could be attributed to the fact that starch granules become sensitive being weaker and easier to break after irradiation. In addition, a consequence of starch radiation-induced degradation can be also the inhibition of granule ability to trap water and provoke the swelling explaining thus the reduction of swelling power by irradiation.

### **3.2. Rheological properties**

Ionizing radiation processing is able to produce significant changes in the rheological properties of starch especially by decreasing its viscosity. In this way, the most studies approached the evaluation of pasting behavior of irradiated starches. Thus, a considerable decrease in the paste viscosities was noted as the irradiation dose increased (up to 500 kGy) for starches with different botanical origins [2, 3, 6, 9, 12, 13, 15–17, 19–23, 27, 31–33, 35, 38]. However, exceptions were reported for the breakdown viscosity that increased with the irradiation dose up to 10 kGy for corn or wheat starches [35, 37, 39]. In addition, a comparative study on corn starch treated with the same gamma irradiation dose (10 kGy) in the dose rate range of 0.4–2 kGy/h clearly revealed that the viscosities of the starch pasting profile decreased more at lower dose rates in comparison to native starch [37].

From the outset, it should be emphasized that the multitude of experimental data reported in a large volume of papers shows that although the gelatinization properties of starch are affected by irradiation, a pattern of alterations cannot be identified. More specifically, it can be claimed that the evolution of gelatinization temperatures and enthalpy is practically unpre-

Aspects on Starches Modified by Ionizing Radiation Processing

http://dx.doi.org/10.5772/intechopen.71626

59

Several investigations [1, 2, 5, 6, 35] reported the decrease of both gelatinization temperatures (onset, peak and conclusion temperatures) and enthalpy as the irradiation increasing (up to 50 kGy) for cereal starches. However, Liu et al. [35] reported that the gelatinization parameters of corn starch almost remained constant under 20 kGy, and afterwards, their significant decrease occurred for irradiation doses up to 500 kGy. Later on, certain decrease in the gelatinization temperatures was reported for corn starch with different amylose content, up to 50 kGy, but only marginal effect on enthalpy values was identified [1]. These results indicated that gamma irradiation caused the production of defective crystalline structure and an increase in the proportion of short chains in amylopectin, which caused a decrease in gelatinization temperature [17]. The decrease in enthalpy value was explained by the disruption of the crystalline domain of starch granules in addition to disruption of double helical order [2, 17]. Other investigations [10] revealed that the gelatinization temperatures and enthalpy had no statistically significant alteration after irradiation with gamma rays for wheat starch treated with irradiation doses up to 50 kGy at a dose rate of 13 Gy/min. More than that, another study [39], using a higher dose rate (1 kGy/h) in the irradiation dose range up to 9 kGy, pointed out no significant difference in gelatinization temperatures and enthalpy for wheat starch after

The investigations on rice starch irradiated at low rate of 0.4 kGy/h, with irradiation doses up to 10 kGy [15], also showed no significant shift of gelatinization temperatures up to 5 kGy, confirming the previously reported results [14], but a decrease of gelatinization temperatures and enthalpy was observed after 10 kGy irradiation. Similar results showing no important alteration of gelatinization parameters were also reported for elephant foot yam starch treated

An extensive study on four varieties of starch extracted from the beans [20] revealed the reduction of the gelatinization temperatures and enthalpy of bean starch by irradiation with doses up to 25 kGy at low dose rate of 185 Gy/h. Contrary, Chung et al. [17] have found that the gelatinization temperatures for bean starch remained unaffected at 10 kGy and increased slightly at 50 kGy (2 kGy/h). An increasing behavior of gelatinization temperatures has also been reported for potato starch exposed to e-beam up to 50 kGy at high dose rate (2 kGy/min) [5], while the gamma irradiation at a dose rate of 2 kGy/h caused the increase of gelatinization temperatures when irradiated at 10 kGy, but decreased at 50 kGy [17]. A significant increase in the onset and peak temperatures was reported while no important effect on the gelatinization enthalpy was noticed for sago starches under irradiation treatment with doses less than 25 kGy [36]. Increase in gelatinization temperatures in irradiated starches was correlated with decreases in the overall crystallinity resulting that among the starch crystallites containing various rigidities, the relatively weak crystalline structure could be preferentially destroyed during irradiation [17].

dictable for various irradiation conditions and types of starch.

with doses up to 25 kGy at a dose rate of 2 kGy/h [19].

irradiation.

The level of radiation-induced changes in the pasting profile was different according to the starch variety [20, 22, 31] and may be assigned to difference in extent of polymerization of leached amylose and amylopectin molecules of each starch variety. The reduction of the peak viscosity of starch was assigned to its weaker water binding capacity, granular rigidity, and integrity due to glycosidic bond cleavage [35, 40]. Moreover, the decrease in the setback and final viscosities were attributed to the degradation or shortening of amylose and longer amylopectin branch chains by irradiation [17, 37].

A gradual decrease of the initial pasting and peak temperatures was also induced by irradiation [3, 9, 17, 19, 21, 32, 33, 35, 37]. Although the peak time was not influenced by irradiation dose rate, it depended on starch variety [31].

Likewise, the apparent viscosity of irradiated starches decreased significantly as the irradiation dose increased for different cereal and tuber starches [4, 5, 8, 10, 11]. Kamal et al. [8] demonstrated that the electron beam effect on the apparent viscosity of corn starch was greater than that of gamma radiation in the early stage of irradiation ~5 kGy. Moreover, a mathematical model was elaborated to describe the exponential decrease of the apparent viscosity against irradiation dose [4]. At the same time, it was proved that each starch is characterized by a material constant that indicates the functional sensitivity of starch to irradiation. Consequently, in technological applications, based on this model and the material constant typical for each starch, one can calculate the irradiation dose required to be applied in order obtain a certain value of the apparent viscosity.

#### **3.3. Gelatinization**

Gelatinization is one of the most important functional properties of starch. Ionizing radiation processing of starch generally leads to great modifications of gelatinization temperatures and process enthalpy due to structural reconfiguration occurring in starch macromolecule. Lately, starch gelatinization is studied and monitored by differential scanning calorimetry (DSC), which is an extremely valuable tool to provide a quantitative measure of the gelatinization enthalpy and a determination of temperature range where gelatinization occurs as well.

From the outset, it should be emphasized that the multitude of experimental data reported in a large volume of papers shows that although the gelatinization properties of starch are affected by irradiation, a pattern of alterations cannot be identified. More specifically, it can be claimed that the evolution of gelatinization temperatures and enthalpy is practically unpredictable for various irradiation conditions and types of starch.

**3.2. Rheological properties**

58 Applications of Modified Starches

rates in comparison to native starch [37].

lopectin branch chains by irradiation [17, 37].

dose rate, it depended on starch variety [31].

obtain a certain value of the apparent viscosity.

**3.3. Gelatinization**

as well.

Ionizing radiation processing is able to produce significant changes in the rheological properties of starch especially by decreasing its viscosity. In this way, the most studies approached the evaluation of pasting behavior of irradiated starches. Thus, a considerable decrease in the paste viscosities was noted as the irradiation dose increased (up to 500 kGy) for starches with different botanical origins [2, 3, 6, 9, 12, 13, 15–17, 19–23, 27, 31–33, 35, 38]. However, exceptions were reported for the breakdown viscosity that increased with the irradiation dose up to 10 kGy for corn or wheat starches [35, 37, 39]. In addition, a comparative study on corn starch treated with the same gamma irradiation dose (10 kGy) in the dose rate range of 0.4–2 kGy/h clearly revealed that the viscosities of the starch pasting profile decreased more at lower dose

The level of radiation-induced changes in the pasting profile was different according to the starch variety [20, 22, 31] and may be assigned to difference in extent of polymerization of leached amylose and amylopectin molecules of each starch variety. The reduction of the peak viscosity of starch was assigned to its weaker water binding capacity, granular rigidity, and integrity due to glycosidic bond cleavage [35, 40]. Moreover, the decrease in the setback and final viscosities were attributed to the degradation or shortening of amylose and longer amy-

A gradual decrease of the initial pasting and peak temperatures was also induced by irradiation [3, 9, 17, 19, 21, 32, 33, 35, 37]. Although the peak time was not influenced by irradiation

Likewise, the apparent viscosity of irradiated starches decreased significantly as the irradiation dose increased for different cereal and tuber starches [4, 5, 8, 10, 11]. Kamal et al. [8] demonstrated that the electron beam effect on the apparent viscosity of corn starch was greater than that of gamma radiation in the early stage of irradiation ~5 kGy. Moreover, a mathematical model was elaborated to describe the exponential decrease of the apparent viscosity against irradiation dose [4]. At the same time, it was proved that each starch is characterized by a material constant that indicates the functional sensitivity of starch to irradiation. Consequently, in technological applications, based on this model and the material constant typical for each starch, one can calculate the irradiation dose required to be applied in order

Gelatinization is one of the most important functional properties of starch. Ionizing radiation processing of starch generally leads to great modifications of gelatinization temperatures and process enthalpy due to structural reconfiguration occurring in starch macromolecule. Lately, starch gelatinization is studied and monitored by differential scanning calorimetry (DSC), which is an extremely valuable tool to provide a quantitative measure of the gelatinization enthalpy and a determination of temperature range where gelatinization occurs Several investigations [1, 2, 5, 6, 35] reported the decrease of both gelatinization temperatures (onset, peak and conclusion temperatures) and enthalpy as the irradiation increasing (up to 50 kGy) for cereal starches. However, Liu et al. [35] reported that the gelatinization parameters of corn starch almost remained constant under 20 kGy, and afterwards, their significant decrease occurred for irradiation doses up to 500 kGy. Later on, certain decrease in the gelatinization temperatures was reported for corn starch with different amylose content, up to 50 kGy, but only marginal effect on enthalpy values was identified [1]. These results indicated that gamma irradiation caused the production of defective crystalline structure and an increase in the proportion of short chains in amylopectin, which caused a decrease in gelatinization temperature [17]. The decrease in enthalpy value was explained by the disruption of the crystalline domain of starch granules in addition to disruption of double helical order [2, 17].

Other investigations [10] revealed that the gelatinization temperatures and enthalpy had no statistically significant alteration after irradiation with gamma rays for wheat starch treated with irradiation doses up to 50 kGy at a dose rate of 13 Gy/min. More than that, another study [39], using a higher dose rate (1 kGy/h) in the irradiation dose range up to 9 kGy, pointed out no significant difference in gelatinization temperatures and enthalpy for wheat starch after irradiation.

The investigations on rice starch irradiated at low rate of 0.4 kGy/h, with irradiation doses up to 10 kGy [15], also showed no significant shift of gelatinization temperatures up to 5 kGy, confirming the previously reported results [14], but a decrease of gelatinization temperatures and enthalpy was observed after 10 kGy irradiation. Similar results showing no important alteration of gelatinization parameters were also reported for elephant foot yam starch treated with doses up to 25 kGy at a dose rate of 2 kGy/h [19].

An extensive study on four varieties of starch extracted from the beans [20] revealed the reduction of the gelatinization temperatures and enthalpy of bean starch by irradiation with doses up to 25 kGy at low dose rate of 185 Gy/h. Contrary, Chung et al. [17] have found that the gelatinization temperatures for bean starch remained unaffected at 10 kGy and increased slightly at 50 kGy (2 kGy/h). An increasing behavior of gelatinization temperatures has also been reported for potato starch exposed to e-beam up to 50 kGy at high dose rate (2 kGy/min) [5], while the gamma irradiation at a dose rate of 2 kGy/h caused the increase of gelatinization temperatures when irradiated at 10 kGy, but decreased at 50 kGy [17]. A significant increase in the onset and peak temperatures was reported while no important effect on the gelatinization enthalpy was noticed for sago starches under irradiation treatment with doses less than 25 kGy [36]. Increase in gelatinization temperatures in irradiated starches was correlated with decreases in the overall crystallinity resulting that among the starch crystallites containing various rigidities, the relatively weak crystalline structure could be preferentially destroyed during irradiation [17].
