Many cereal proteins, such as wheat, corn, and oat proteins, have high levels of the amide-containing amino acids, glutamine and asparagine. These side chains are susceptible to hydrolysis of the amide bond, which leads to release of ammonia and transformation to acidic groups. The released ammonia has been implicated in the formation of aroma compounds and pigments because of its participation in the Maillard browning reaction. The conversion of the amide groups to acid groups may partially unfold the protein, resulting in an amphiphilic molecule that can be used as a surface active agent or emulsifier by food processors. This review provides general information on the factors that affect deamidation of proteins as well as the implications of deamidation for food processing.

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The effect of three parameters on deamidation levels during twin-screw extrusion of wheat flour was studied: temperature, feed moisture content, and pH. This was accomplished by generating three sets of extrudates. The first set varied temperature (130, 155, and 170 °C), the second set varied feed moisture content (20%, 25%, and 30%), and the third set varied pH of the liquid feed (3.0, 7.0, and 12.0). In each set all other parameters were held constant. It was found that increases in temperature and feed moisture enhanced deamidation and that deamidation was also favored at extremes of pH. Possible explanations for these trends are discussed.

The volatiles generated from an extruded autolyzed yeast extract (AYE) were isolated and analyzed by GC and GC-MS. The volatile profile of the extruded AYE was compared with that of the unextruded ingredient. It was found that the same volatiles were formed in both cases and that the only difference was in the amounts formed. In both systems a total of 9 sulfur-bearing volatiles, 5 volatiles characteristic of sugar degradation, and 39 nitrogen-containing heterocyclics were identified. The overall profile was dominated by alkylpyrazines, and extrusion was found to enhance the formation of pyrazines considerably.

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