Evaluation of the in vitro α-glucosidase inhibitory activity of green tea polyphenols and different tea types

BACKGROUND: The objective of this study was to determine whether green tea, black tea and oolong tea have inhibitory potential against alpha-glucosidase which may be used to control postprandial hyperglycemia in type 2 diabetes mellitus. RESULTS: Green tea polyphenols (TPs) strongly inhibited alpha-glucosidase activity by non-competitive inhibition with an IC50 value of 2.33 mu g mL(-1) and the inhibitory effect was dependent on TP concentration and incubation order. Green tea, black tea and oolong tea also had dose-dependent inhibitory potential with IC50 values of 2.82, 2.25 and 1.38 mu g mL(-1) (mu g polyphenol m(L-1)), respectively. The study also showed that the content of unprecipitated TPs changed during enzymatic hydrolysis, leading to the change of the antioxidant activity. The change of the antioxidant activity of tea extracts revealed a similar trend to that of green TPs during enzymatic hydrolysis. CONCLUSION: Green TPs, green tea, black tea and oolong tea are excellent alpha-glucosidase inhibitors and their inhibitory potency is mainly attributed to TPs. These findings suggest that green tea, black tea and oolong tea can potentially be used to control postprandial hyperglycemia. (C) 2015 Society of Chemical Industry