Presence and Activity of Various Amylases in Rice: Effect on Texture and Leached Sugar Composition during Cooking

Abstract

Amylase isozymes from non-glutinous japonica and indica rice types showed various band patterns, strengths and intensities based on zymography. Major bands were presumed to be α- and β-amylase according to their molecular weights; other amylases, 270 and 200 kDa in size, were also detected. Three debranching enzymes (DBEs) were detected from the dye pattern as well. Amylase activities were observed at pH 7.0 during rice cooking. However, the α-amylase activity at pH 7.0 was 50% lower than that at pH 5.0; DBE, β-amylase, and α-glucosidase values were similarly reduced by 25%, 90% and 99%, respectively. α-Amylase activity and DBE activities correlated positively with both the amount of malto-oligomer leached during rice cooking and the adhesiveness of cooked rice. Thus, it is considered that the activity of amylase isozymes affects the palatability of cooked rice. Therefore, enzymes from rice endosperm may represent a new and highly useful biomarker for evaluating the palatability of cooked rice.