Catechins play key role in green tea extract-induced postprandial hypoglycemic potential in vitro

Green tea is often associated with glycemic control benefit. However, the available evidence is not conclusive. In this study, we systematically assessed the contribution of main green tea extract (GTE) ingredients to the inhibition of carbohydrate digestive enzyme and intestinal glucose transport, which are two intervention options for postprandial blood glucose control. A catechin mixture (CM) solution containing seven catechins and epigallocatechin gallate (EGCG) solution was prepared based on the contents of individual catechins in the GTE as determined by high-performance liquid chromatography. The inhibitory potency of GTE, CM, and EGCG on alpha-amylase or alpha-glucosidase was compared in cell-free system. GTE's inhibitory potency was mainly attributed to catechins, among which, EGCG accounted for at least 80 % of the alpha-amylase inhibitory activity and 90 % of the alpha-glucosidase inhibitory activity of GTE. In addition, the fluorescence quenching of the digestive enzymes by EGCG revealed that the binding site of EGCG-alpha-amylase was 1.2, and that for EGCG-alpha-glucosidase to be 2.0. The inhibitory potency of GTE, CM, and EGCG on glucose transport was assessed in Caco-2 monolayer system. Under the simulated fasting state, there was significant difference between the test materials regarding inhibitory potency according to two-way ANOVA (P > 0.05). Under the simulated fed state, CM showed stronger inhibition than EGCG only at the highest test concentration (25.7 mu g/mL), while no significant difference was observed between CM and the GTE. In conclusion, our results suggest that green tea's postprandial hypoglycemic potential can be attributed to its catechins.