Antioxidant activity and α-amylase and α-glucosidase inhibitory activity of a fermented tannic acid product: Trigalloylglucose

Small molecules with beneficial biological activities can be generated by controlled fermentation of natural food products. In this study, the fermentation products of tannic acid by Aspergillus carbonarius FCYN212 were isolated and identified. Two major chemical structures were obtained: gallic acid (GA) and 3,4,6-tri-O-galloyl- d -glucose (TGG). GA and TGG exhibited stronger free radical scavenging ability and ferric-reducing power than butylated hydroxyanisole (BHA). Additionally, TGG demonstrated significant dose-dependent enzyme inhibitory activities against α-amylase and α-glucosidase with IC50 values of 334.6 ± 8.9 and 46.5 ± 1.6 μM, respectively. Notably, TGG was a mixed type inhibitor of α-amylase and α-glucosidase according to a Dixon plot. This study revealed the antioxidant and enzyme inhibitory potential of TGG isolated from a fermented extract of tannic acid. TGG may therefore serve as an antioxidant and antidiabetic ingredient in functional or medical foods.