Inhibiting hydrolytic enzyme activity and slowing carbohydrate digestion using lotus seed epicarp phenolic extracts

This study investigated the hypoglycaemic activity of lotus seed epicarp phenolic extract (LSEPE) by inhibiting starch hydrolytic enzyme activity and slowing down carbohydrate digestion. Total phenolic and flavonoid contents in LSEPE were 620.37 ± 10.45 mg GAE/g DW and 422.69 ± 23.57 mg RE/g DW, respectively. A total of 57 phenolic compounds were first identified in LSEPE. The IC₅₀ of LSEPE for inhibiting α-amylase and α-glucosidase were 124.44 ± 2.89 μg/mL and 0.99 ± 0.02 μg/mL, approximately 3.28 to 1.61 times that of acarbose. LSEPE acted as a mixed-type inhibitor of α-amylase and an anti-competitive-type inhibitor of α-glucosidase. UV spectroscopy, fluorescence quenching, and CD analysis showed that LSEPE could change the enzymes' microenvironment and hydrophobicity. Moreover, LSEPE slowed the starch hydrolysis rate <i>in vitro</i> and increased the proportions of slowly digestible starch (SDS) and resistant starch (RS) by 60.51% and 19.98%. Therefore, the lotus seed epicarppolyphenols could be the potential natural ingredients for developing anti-hyperglycemic functional foods.