Longan seed polyphenols inhibit α-amylase activity and reduce postprandial glycemic response in mice

The effects of longan seed polyphenols (LSPs) on postprandial glycemic response in mice were investigated, enzyme inhibition kinetics of LSPs against α-amylase were studied using an inhibition assay in vitro, and the underlying mechanisms were discussed by analyzing the impacts of LSPs on the structure of α-amylase using multispectral approaches. The results showed LSPs significantly suppressed blood glucose response in a dose-dependent manner. Enzyme inhibition analysis demonstrated LSPs inhibited α-amylase activity in a mixed type (IC₅₀ 3.02 mg mL^-1). UV-vis absorption spectroscopy and fluorescence quenching spectroscopy suggest LSPs tend to bind with α-amylase through static interaction at one binding site, mainly through hydrogen bonding and van der Waals forces. The secondary structure of α-amylase was changed by LSPs as reviewed by circular dichroism, showing a more compact skeleton and more flexible loop of α-amylase. This hinders the substrate from reaching the binding site of the enzyme, resulting in reduced enzyme activity. These suggest the potential application of LSPs as a hypoglycemic agent in functional foods.