2.1.3. Sprouted kernels

presents in the ripe seed coat. Bechtel et al. [17] mentioned that color of wheat caryopses varies from light buff or yellow to red-brown according to the absence or presence of red pigmentation in this layer. Wheat is commonly classed according to color as red or white. Sometimes the perception of grain color is affected by the texture of the endosperm since the soft portion presents air-starch and air-protein interfaces that impart the chalky or dull appearance. On the other hand, the absence of voids or microscopic spaces in the endosperm of hard wheat gives a glassy or vitreous appearance resulting in trends of the red coloration present in the seed coat. Other factors may affect the natural color of kernels such as mold-infestation in the field or during storage, heat or frost damage and other caused by phytopathogens. Shahin et al. [18] reported that mildew growth on wheat kernels reduces grain quality due to the characteristic

Computer-aided image analysis has many applications in agricultural sciences. For assessing grain quality this technique is able to objectively determine shape and color. However, problems are encountered in practical applications of these methods because they rarely correlate with the examined attributes and therefore a multivariate analysis is required. Principal component analysis (PCA)—a variant of the above method—is used when a high number of variables have to be reduced to several components [19]. Image analysis is performed by algorithms that use different color, texture and shape features as input parameters [20].

Actually, interest in white wheat kernels by both the milling and baking industries is increasing, because refined and mainly whole grain flours milled are preferred for different products and applications. Hard white wheat has been reported to have distinct advantages over the conventional hard red counterpart. These advantages include higher flour extraction rate and

One of the most relevant wheat kernel quality parameters is insect damage. This particular assessment is considered one of the most critical degrading factors [22], because it relates to flour yield and color and increases the amounts of insect fragments present in flours and processed products which are considered as one of the most important quality factors related to food sanitation. Presence of insects induces losses in quantity and quality by insect consumption, grain weight loss, contamination (toxicity) with excrement, bodily fragments and chemical secretions that disfavor flour flavor and odor. In addition, insects increase heat and kernel moisture due to their metabolic activity. The potent enzymes produced by insects and by the grain respiration system are known to negatively affect milling and baking qualities [23, 24].

The main group of insects that cause serious damage in cereal grains includes beetles such as Sitophilus granarius, Tribolium castaneum, Trogoderma granarium, Tenebroides mauritanicus and Rhyzopertha dominica. Primary pests infest sound grain whereas secondary pests can attack only broken or cracked grains or milled products [25]. A large portion of the insect's life is spent inside the kernels; therefore, their detection is extremely difficult. Fortunately, the industry has adopted new techniques for identification of insect damage inside grains using Near

gray discoloration which negatively impacts color of refined flours.

lighter colored end products [21].

278 Wheat Improvement, Management and Utilization

2.1.2. Insect damage

Sprouted kernels are easily detected by visual observation such as kernel swelling, growth in the germ area, discoloration of the germ, the split of the bran over the germ and mainly by the detection of the emergence of the radicle or rootlets and coleoptile or acrospires [6, 28]. Sprouting can occur both, in the field or during storage when kernels absorb moisture and are exposed to appropriate temperature conditions [5]. This germination process involves several biochemical changes in the endosperm of the kernel, such as synthesis and release of amylolytic, lipolytic, fibrolitic and proteolytic enzymes that degrade starch, oil, fiber and proteins, respectively [5, 28]. The presence of sprouted damage level usually is determined quantitatively by measuring the amount of α-amylase using the Falling Number (FN) [29] or by determining peak viscosity with the Rapid Visco Analyser (RVA) [28]. In the industry, different unfavorable technical factors are associated with the use of sprouted kernels such as reducing milling yield and lowering flour quality, sticky doughs and significant effects in the baking quality of bread wheat [6, 28]. Sprouted kernels usually yield darker colors due to the presence of significant amounts of reducing sugars and degraded proteins that upon heating form higher amounts of Maillard reaction products [5].

#### 2.1.4. Heat damage

Heat damage in kernels is mainly attributed to two major reasons: first, faulty storage of damp grain and second, as a consequence of an inadequate (high) artificial drying [6]. Grains stored at high moisture-induced elevated respiration rates, consequently metabolic activation of the grain, causing heat, mold growth and possible insect infestation [5]. A darker color in the grain is indicative of heat damage, however sometimes this type of damage is not usually visible and requires testing and it is necessary in most cases to cut the kernels to determine if the color of the cross-section is reddish-brown. Wheat doughs produced from heat-damaged flours are sticky due to the partial degradation of starch granules and gluten proteins by amylases and proteases, respectively. In addition, the bread crumb is darker due to the higher reducing sugars and hydrolyzed proteins that promote browning reactions upon baking. Therefore, the gluten protein and rheological testing are required to evaluate effects of this defect. Heat damaged seeds are usually associated to the loss of viability [5, 6].

### 2.1.5. Frost damage

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 affecting negatively baking performance [6].
