Inhibitory effects of acorn (Quercus variabilis Blume) kernel-derived polyphenols on the activities of α-amylase, α-glucosidase, and dipeptidyl peptidase IV

Abstract

Abstract The chemical constituents of the free and bound polyphenols extracted from acorn kernels were analyzed, and the predominant chemical components in the free polyphenol extract were quercetin, azelaic acid, and gallic acid, while the bound polyphenol extract mainly contained ellagic acid, gallic acid, and ferulic acid. The inhibitory activities of the four main components on α-glucosidase showed the following trend: ellagic acid\xa0>\xa0quercetin\xa0>\xa0azelaic acid\xa0>\xa0gallic acid. The IC50 values of the free and bound polyphenol extracts on α-amylase were 5.25 and 1.37\xa0mg/mL, respectively. The free polyphenol extract exhibited a greater ability to inhibit α-glucosidase and dipeptidyl peptidase IV (DPP-IV) than the bound polyphenol extract. The polyphenols were found to change the secondary structures of α-amylase, α-glucosidase and DPP-IV. The inhibitory effects of the polyphenols on the three enzymes may give rise to low postprandial blood glucose after eating acorn-containing foods and can be beneficial to diabetics.