2.1.6. Mold damage

Wheat grains represent an important substrate for the development of different types of molds which affect adversely the grain quality. Serna-Saldivar [5] specifies that the genus Fusarium, Alternaria and Penicillum are the fungus most frequently isolated from wheat infested negatively grains. Growth of fungi in stored wheat affects yield and relevant quality factors such as discoloration, germination, free fatty acid value, falling number and dough rheological properties [31], because molds produce important enzymes such as amylases, proteases and lipases.

Presence of mold in the grain also causes production of undesirable odors and grains infested with Fusarium and/or Aspergillus will probably contain significant amounts of mycotoxins (secondary metabolites produced by the fungi) that endanger human and animal health [5]. Fungal species that attack cereal grains can be classified into two groups: field fungi (less aggressive) and storage fungi. Temperatures between 30 and 35°C and moisture content in the grain above 15% are the conditions for the optimal development of fungi in storage [31].

#### 2.2. Shape and size

#### 2.2.1. Grain morphology

The wheat grain or kernel—botanically named caryopsis—is a particular dry fruit and indehiscent consisting of three main regions are easily recognizable: pericarp, endosperm and germ (which includes the embryo) [25]. The geometric properties such as size and shape are one of most important physical properties considered during cereal grains processing, due to its morphology can be associated with quality parameters. Grains are considered like spheres or ellipse because of their irregular shapes [13].

Wheat shape can be described as round (approaching spheroid). Morphologically, Evers and Millar [32] describe that wheat kernel presented a marked crease, a re-entrant region on the ventral side, extending along the grain's entire length and deepest in the middle; however, variation occurs in the thickness, large and width of the grain. The shape of the groove is a characteristic feature of some species and cultivars.

#### 2.2.2. Axial dimensions

2.1.5. Frost damage

2.1.6. Mold damage

lipases.

storage [31].

2.2. Shape and size

2.2.1. Grain morphology

ellipse because of their irregular shapes [13].

characteristic feature of some species and cultivars.

ing negatively baking performance [6].

280 Wheat Improvement, Management and Utilization

The degree of tolerance shown by wheat kernels on the field to low or freezing temperatures depends largely on the stage of development at which the stress occurs. Wheat is most susceptible to frost damage at flowering, being particularly harmful when it occurs during grain filling [6, 30]. Frosted grains are creased along the long axis and creases are regular or uniform, unlike grains with moisture stress in which this anomaly is not uniform. Sometimes, frosted grains will have a blue-gray appearance [30] and usually lower 1000-kernel weight because they did not fill properly [5]. The premature death of the kernel results in less polymeric protein synthesis and consequently their gluten functionality is compromised affect-

Wheat grains represent an important substrate for the development of different types of molds which affect adversely the grain quality. Serna-Saldivar [5] specifies that the genus Fusarium, Alternaria and Penicillum are the fungus most frequently isolated from wheat infested negatively grains. Growth of fungi in stored wheat affects yield and relevant quality factors such as discoloration, germination, free fatty acid value, falling number and dough rheological properties [31], because molds produce important enzymes such as amylases, proteases and

Presence of mold in the grain also causes production of undesirable odors and grains infested with Fusarium and/or Aspergillus will probably contain significant amounts of mycotoxins (secondary metabolites produced by the fungi) that endanger human and animal health [5]. Fungal species that attack cereal grains can be classified into two groups: field fungi (less aggressive) and storage fungi. Temperatures between 30 and 35°C and moisture content in the grain above 15% are the conditions for the optimal development of fungi in

The wheat grain or kernel—botanically named caryopsis—is a particular dry fruit and indehiscent consisting of three main regions are easily recognizable: pericarp, endosperm and germ (which includes the embryo) [25]. The geometric properties such as size and shape are one of most important physical properties considered during cereal grains processing, due to its morphology can be associated with quality parameters. Grains are considered like spheres or

Wheat shape can be described as round (approaching spheroid). Morphologically, Evers and Millar [32] describe that wheat kernel presented a marked crease, a re-entrant region on the ventral side, extending along the grain's entire length and deepest in the middle; however, variation occurs in the thickness, large and width of the grain. The shape of the groove is a In a wheat kernel, three principal dimensions are commonly measured: length (L), width (W) and thickness (T) (Figure 1), which typically are determined using a micrometer or caliper and reported in millimeters. The principal axial dimensions of grains are useful in selecting sieve separators and for the calculation of extraction rate during size reduction [33]. These measurements can also be used to calculate volume of kernels, which are important during modeling of grain drying, aeration, heating and cooling. The effects of size and surface area on drying rates of particulate materials can also be characterized by using the surface to volume ratio [34]. The kernels at the spikelet had different individual mass. The dimensions of the wheat kernels within a plant varied significantly and the development rates and dimensions of kernels are different [35].

Figure 1. Axial dimensions in a wheat kernel. (a) Length (L) and thickness (T); (b) width (W).

Small kernels are considered to have less potential flour yield and inferior milling properties. Gaines et al. [36] discussed that soft wheat cultivars differed in their average kernel size and in the size distribution of their kernels. However, they found that kernel characteristics, milling performance and soft wheat end-use qualities were not influenced by kernel size, except that small kernels tended to be softer. The milling and baking properties of smaller kernels were not found to be inferior to larger counterparts, but were equivalents. Aversely, Morgan et al. [37] reported that "in general, as kernel size declines, flour yield and flour refinement (ash and color) are adversely affected", but agrees that small kernels were softer than large kernels.

Dholakia et al. [9] proposed an interesting factor-form-density (FFD) for phenotypic measurement on wheat kernels from described the differences in the grain structure (density) and the deviation from the cylindrical form, which was compiled as:

$$\text{FFD} = \frac{\text{Kernel weight}}{\text{Kernel length} \times \text{kernel width}}.\tag{1}$$

#### 2.2.3. Sphericity

Sphericity (φ) expresses the characteristic shape of a solid object relative to that of a sphere of the same volume. The longest diameter (major) and shortest diameter (minor) will adequately describe the size of an ellipsoidal object such as the wheat kernel [4]. Bayram [38] suggested that the determination of the sphericity is usually difficult and not practical, due to irregular shape of the granular material and it is the calculation of the exact volume and surface area, involving multiple length measurements. In this sense, this author proposed a novel and easily model to determine the sphericity of granular materials, following the next expression:

$$\phi\_s = \frac{\Sigma(D\_i \\_\text{\overline{D}})^2}{\left(\overline{\text{D}}N\right)^2},\tag{2}$$

where φ<sup>s</sup> = sphericity value, Di = any measured dimension, D = average dimension or equivalent diameter and N = number of measurements. Increase in the N increases the accuracy. In Eq. (2), when φ<sup>s</sup> for a sphere is 0, that is, an increase in φ<sup>s</sup> value using Eq. (2) shows the deviation from the sphericity.

#### 2.2.4. Roundness

Mohsenin [39] defined roundness as the measure of the sharpness of the corners of a solid, whereas Curray [40] proposed the next equations for estimating roundness under different conditions of geometry and application:

$$\text{Roundness} = \frac{A\_p}{A\_c},\tag{3}$$

where Ap = largest projected area of object in natural rest position and Ac = area of smallest circumscribing circle. The object area is obtained using the next equation:

$$\text{Roundness} = \frac{\sum r}{NR},\tag{4}$$

where r = radios of curvature as defined in Figure 2, R = radius of the maximum inscribe circle, N = total numbers of corners summed in numerator.

Grading Factors of Wheat Kernels Based on Their Physical Properties http://dx.doi.org/10.5772/67246 283

$$\text{Roundness} = \frac{r}{R},\tag{5}$$

where R in this case is the mean radius of the object and r is the radius of curvature of the sharpest corner. The objection to this method is that the radius of curvature of a single corner determines the roundness or flatness (Figure 2).

not found to be inferior to larger counterparts, but were equivalents. Aversely, Morgan et al. [37] reported that "in general, as kernel size declines, flour yield and flour refinement (ash and color) are adversely affected", but agrees that small kernels were softer than large kernels.

Dholakia et al. [9] proposed an interesting factor-form-density (FFD) for phenotypic measurement on wheat kernels from described the differences in the grain structure (density) and the

Sphericity (φ) expresses the characteristic shape of a solid object relative to that of a sphere of the same volume. The longest diameter (major) and shortest diameter (minor) will adequately describe the size of an ellipsoidal object such as the wheat kernel [4]. Bayram [38] suggested that the determination of the sphericity is usually difficult and not practical, due to irregular shape of the granular material and it is the calculation of the exact volume and surface area, involving multiple length measurements. In this sense, this author proposed a novel and easily

Kernel length · kernel width : (1)

<sup>2</sup> , (2)

, (3)

NR , (4)

FFD <sup>¼</sup> Kernel weight

model to determine the sphericity of granular materials, following the next expression:

<sup>φ</sup><sup>s</sup> <sup>¼</sup> <sup>Σ</sup>ðDi <sup>−</sup> <sup>D</sup><sup>Þ</sup>

ðDNÞ

where φ<sup>s</sup> = sphericity value, Di = any measured dimension, D = average dimension or equivalent diameter and N = number of measurements. Increase in the N increases the accuracy. In Eq. (2), when φ<sup>s</sup> for a sphere is 0, that is, an increase in φ<sup>s</sup> value using Eq. (2) shows the

Mohsenin [39] defined roundness as the measure of the sharpness of the corners of a solid, whereas Curray [40] proposed the next equations for estimating roundness under different

Roundness <sup>¼</sup> Ap

where Ap = largest projected area of object in natural rest position and Ac = area of smallest

where r = radios of curvature as defined in Figure 2, R = radius of the maximum inscribe circle,

Roundness ¼

circumscribing circle. The object area is obtained using the next equation:

Ac

<sup>X</sup> r

2

deviation from the cylindrical form, which was compiled as:

282 Wheat Improvement, Management and Utilization

2.2.3. Sphericity

deviation from the sphericity.

conditions of geometry and application:

N = total numbers of corners summed in numerator.

2.2.4. Roundness

Figure 2. Roundness as defined by geologists to describe shape of grains and pebbles (adapted from Mohsenin, 1978).

Higher values of sphericity and roundness indicate that the shape of the kernel is closer being spherical. It is important to know sphericity and roundness—for example, before handling or dryer process—so that this efficiency increases.

It is important noted that the main influence is not the shape and size per se, but the degree of variation in these attributes within a sample [17]. Wheat kernel size, like most of the traits of biological interest and agricultural importance, is a complex character and is suggested to be quantitative in nature, although kernel size and shape have emerged as important breeding objectives [9].

### 2.3. Volume weight and density

Unit volume weight indicates the density and compactness for a given volume of grain; a minimum test weight requirement is generally one of the primary specifications used in wheat grading and classification [6]. Test weight or density in wheat kernels is a physical quality characteristic considered mainly by flour and semolina millers. In general, high weight (accordance to wheat class) may indicate a grain sample healthy and optimum appearance, whereas low weight can occur as result of one or more adverse events such as insect damage, heat stress or delayed harvesting [41].

Bulk density and true density can be useful for storage facilities, because affect the rate of heat and mass transfer of moisture during aeration and drying process [33]. In addition of these two parameters, porosity can be useful in sizing grain hoppers and storage facilities [42]. In the grain industry, the ratio weight-volume commonly is report in bushels units or kg/hL (100 L) [4]. Test weight per bushel is the weight of the grain required to fill a level Winchester bushel measure 2150.42 in<sup>3</sup> (35.24 L) capacity [16]. The conversion factors of pounds per Winchester bushel and pounds per imperial bushel (2219.36 in3 ) to kg/hL are 1.297 and 1.247, respectively. This test is related to the true grain density, which is affected by grain condition, grain texture and protein content. Wheat kernel sample affected by insect attack, molds or any other damage had a lower test weight when compared with a healthy sample [5].

### 2.3.1. Bulk density

Space occupying by amount of material per volume unit is call density (ρ) and is expressed in units of mass per unit volume. True density (ρ<sup>t</sup> ) is defined as the ratio of the volume of particles and can be determined using the water [43] or by gas [33] displacement methods which determine the volume of the sample. Unfortunately simple techniques as water displacement can result in errors especially if the water penetrates into the kernel [39]. In kernel volume (V) exists interstitial air spaces with different values of particle density and bulk density. Particle density is the mass divided by the volume of the particle alone. The mass of a group of individual particles divided by the space occupied by the entire mass (volume) including the air space is bulk density (ρb). This could be calculated from the following relation [42]:

$$
\rho\_b = \frac{W\_s}{V\_s},
\tag{6}
$$

where the <sup>ρ</sup><sup>b</sup> = bulk density (kg/m<sup>3</sup> ), Ws = weight of the sample (kg) and Vs = volume occupied by the sample (m3 ).

The irregular shape and porous nature of agricultural materials present difficult problems in volume and density measurements. The density of a material has a significant effect on its mechanical characteristics [39]. According to Molenda and Horabik [44], the determination of the bulk density is based on measurement of the mass of a granular material poured freely into a cylindrical container of constant volume, typically 0.25 or 1 dm<sup>3</sup> . Grain density usually varies within a relatively broad range, depending on the species and cultivar, manner of silo, height of deposit, degree of contamination of the grain and other factors. It is recommended to estimate the density of a granular material in a silo by assuming an average density increase of 6% with relation to the density value determined from the mass of 1 hL.

#### 2.3.2. Porosity

Higher values of sphericity and roundness indicate that the shape of the kernel is closer being spherical. It is important to know sphericity and roundness—for example, before handling or

It is important noted that the main influence is not the shape and size per se, but the degree of variation in these attributes within a sample [17]. Wheat kernel size, like most of the traits of biological interest and agricultural importance, is a complex character and is suggested to be quantitative in nature, although kernel size and shape have emerged as important breeding

Unit volume weight indicates the density and compactness for a given volume of grain; a minimum test weight requirement is generally one of the primary specifications used in wheat grading and classification [6]. Test weight or density in wheat kernels is a physical quality characteristic considered mainly by flour and semolina millers. In general, high weight (accordance to wheat class) may indicate a grain sample healthy and optimum appearance, whereas low weight can occur as result of one or more adverse events such as insect damage, heat stress

Bulk density and true density can be useful for storage facilities, because affect the rate of heat and mass transfer of moisture during aeration and drying process [33]. In addition of these two parameters, porosity can be useful in sizing grain hoppers and storage facilities [42]. In the grain industry, the ratio weight-volume commonly is report in bushels units or kg/hL (100 L) [4]. Test weight per bushel is the weight of the grain required to fill a level Winchester bushel measure 2150.42 in<sup>3</sup> (35.24 L) capacity [16]. The conversion factors of pounds per Winchester

This test is related to the true grain density, which is affected by grain condition, grain texture and protein content. Wheat kernel sample affected by insect attack, molds or any other

Space occupying by amount of material per volume unit is call density (ρ) and is expressed

particles and can be determined using the water [43] or by gas [33] displacement methods which determine the volume of the sample. Unfortunately simple techniques as water displacement can result in errors especially if the water penetrates into the kernel [39]. In kernel volume (V) exists interstitial air spaces with different values of particle density and bulk density. Particle density is the mass divided by the volume of the particle alone. The mass of a group of individual particles divided by the space occupied by the entire mass (volume) including the air space is bulk density (ρb). This could be calculated from the following

damage had a lower test weight when compared with a healthy sample [5].

) to kg/hL are 1.297 and 1.247, respectively.

) is defined as the ratio of the volume of

dryer process—so that this efficiency increases.

284 Wheat Improvement, Management and Utilization

bushel and pounds per imperial bushel (2219.36 in3

in units of mass per unit volume. True density (ρ<sup>t</sup>

objectives [9].

2.3. Volume weight and density

or delayed harvesting [41].

2.3.1. Bulk density

relation [42]:

Porosity (ɛ) is the percentage of air between the particles compared to a unit volume of particles [4] and can be calculated from bulk and true density values, using the following relationship proposed by [39]:

$$
\varepsilon = \frac{\rho\_t - \rho\_b}{\rho\_b} \times 100,
\tag{7}
$$

where <sup>ɛ</sup> = porosity (%), <sup>ρ</sup><sup>t</sup> = true density (kg/m<sup>3</sup> ), <sup>ρ</sup><sup>b</sup> = bulk density (kg/m3 ).

Wheat endosperm is mostly composed of starch granules, protein matrix and pores or air voids. Starch granules are bound to one other by the continuous protein matrix. Topin et al. [45] performed an interesting study in which it was determined that two parameters played a major role in the fracture behavior of the wheat endosperm: the matrix volume fraction ρ<sup>m</sup> and the particle-matrix adhesion σpm. The value ρ<sup>m</sup> ranged from 0.04 to 0.2. At ρ<sup>m</sup> = 0.2, the whole interstitial space is filled with the protein matrix, corresponding to zero porosity. In this sense, these authors suggested that the crack of the endosperm depends more on protein content than on the starch-granule adherence, because "the stress inhomogeneities, which are responsible for the stress concentration factor, are more sensitive to the porosity than to adherence among the constituents".

In grains, low porosity will have greater resistance to water vapor escape during the drying process, which may lead to higher power to drive the aeration fans [33]. The porosity of the bulk is the ratio of the volume of the internal pores within the kernels to its bulk volume [43]. Porosity values in wheat kernels increased slightly as the moisture content increased [42].

#### 2.3.3. Thousand kernel weight

Thousand kernel weight (TKW) measures the mass of the wheat kernel and is an essential parameter for the selection of cultivars with the best physical and physiological seed quality. Generally, higher TKW values are positively related to potential flour extraction or yield [46], because this property is closely related to grain size and proportion of endosperm to germ and pericarp tissues [5]. Wheat breeders and flour millers employ this method as a complement to test weight to better describe wheat kernel composition and potential flour extraction [16]. TKW could be used as an index of wheat milling value and is a good parameter for evaluation of kernels as seed material [11]. When the grain is undamaged may be expected high test weight, due to a greater endosperm to bran ratio [29].

Finally, it is important to highlight that grain moisture content has deep influence on the physical properties, particularly those related with volumetric grain weight and density in bulk as it modifies surface properties of seed-coat as well as the properties of kernel endosperm. Several studies [34, 42, 43, 47] have reported the effect of moisture content on different wheat kernel physical properties and concluded that increasing of moisture content level increased axial dimensions, thousand kernel weight, porosity, kernel volume and sphericity, while bulk density decreased. Higher grain moisture content results in an increase in susceptibility of grains to deformation, thus physical properties of cereal grains vary as a function of moisture content [13, 44].
