Evaluation of Total Flavonoids, Myricetin, and Quercetin from Hovenia dulcis Thunb. As Inhibitors of α-Amylase and α-Glucosidase

This study was designed to investigate the inhibition effect and mechanism of total flavonoids, myricetin and quercetin extracted from Hovenia dulcis Thunb. on alpha-amylase and alpha-glucosidase in order to explore the potential use of Hovenia flavonoids in alleviating postprandial hyperglycemia. The results demonstrate that total flavonoids, myricetin, and quercetin were effective inhibitors of alpha-amylase with IC50 values of 32.8, 662 and 770 mu g ml(-1), respectively. And all three were effective inhibitors of alpha-glucosidase with IC50 values of 8, 3 and 32 mu g ml(-1), respectively. Enzyme kinetics tests and Lineweaver-Burk results showed the inhibition effects of total flavonoids, myricetin and quercrtin on alpha-amylase were all reversible and competitive, and the effects on alpha-glucosidase were all reversible but non-competitive. This study revealed that Hovenia flavonoids, especially myricetin, are effective and promising functional foods in alleviating type 2 diabetes mellitus.