Slowing down of starch hydrolysis of glutinous rice and non-glutinous rice flours by black soybean extracts: Cooperation between cyanidin 3-O-glucoside and procyanidins

Abstract

Black soybean (BSB), which contains cyanidin 3-O-glucoside (C3G) and procyanidins, is an ordinary ingredient in Japan. The BSB extracts slowed down pancreatin-induced reducing sugar formation and starch hydrolysis more significantly in non-glutinous rice flour (joshin-ko) than glutinous rice flour (mochi-ko), suggesting that BSB components inhibited amylose digestion more effectively than amylopectin digestion. In the components, C3G, a procyanidin dimer (proB2), and procyanidin oligomers were included. C3G could cooperate with proB2 for the inhibition. Procyanidin oligomers inhibited the amylose hydrolysis significantly but slightly the reducing sugar formation in joshin-ko, and inhibited the both reactions slightly in mochi-ko, suggesting that the oligomers could effectively inhibit amylose digestion. C3G could also cooperate with the procyanidin oligomers to inhibit amylose digestion in joshin-ko. The above results suggest that the cooperation of C3G and procyanidins might also be included in the BSB extract-dependent inhibition of amylose digestion in joshin-ko.

Keywords

• Black soybean
• Cooperation of flavonoids
• Cyanidin 3-O-glucoside
• Inhibition of amylose and amylopectin digestion
• Procyanidins
• Rice flours