Characterization of α-amylase in wheat and maize

Abstract

Alpha-amylase is a starch-hydrolyzing enzyme and its characterization is an important quality parameter in cereal grains. In breadmaking, adequate α-amylase activity is required to produce bread of good quality. High α-amylase activity degrades the flour quality because it hydrolyses excessive amounts of flour starch and lowers flour viscosity which results in a sticky loaf and poor texture. The primary cause of high α-amylase activity is pre-harvest sprouting when the mature grains attached on the ear germinate in the field under wet and cold conditions. Moreover, some cereal cultivars produce unacceptable high α-amylase activity in the absence of pre-harvest sprouting as well. Therefore, α-amylase is influenced by both cultivar and environment factors. This study investigated the influence of cultivar and environment on α-amylase characterization during grain development stages in wheat and maize, and the relationship between α-amylase characterization and chemical composition of grains in both cereals. The results in wheat and maize experiments showed that α-amylase activity changed considerably during grain development stages, with the highest activity was at milk-ripe grains. Regarding to wheat experiment, the grains of cv. Amaretto exhibited higher α-amylase activity than those of cv. Cubus at three grain development stages, irrespective of locations. The α-amylase activity of cultivars grown in Torland was significantly higher (p ≤ 0.05) at dough-ripe and mature-harvest stages than those in Gladebeck, irrespective of cultivars. Regarding to maize experiment, α-amylase activity in mature-harvest grains cultivated in 2011 was significantly (p ≤ 0.05) higher than those in 2010, irrespective of cultivars and within a cultivar except cv. PR39F58. Our results indicate that the difference in the activity of α-amylase was mainly attributed to environments, although the effect of different cultivars was also highly significant. The results of biochemical and kinetic characterization of α-amylase from both wheat and maize have practical uses in the hydrolysis process of starch by food industries such as breadmaking, beers, beverages, syrups and others. This work shows the applicability of four investigated maize cultivars cvs. Benecia, EsBombastic, Franki and PR39F58 for use as a source of α-amylase in starch hydrolysis process. On other hand, thermal activity of amylase isolated from cv. Amaretto is not a desirable feature in the case of using that cultivar as a source of exogenous amylase in order to optimize flour in breadmanking industry.