Discovery of a new tannin compound as an -glucosidase inhibitor from Carya cathayensis Sarg. kernels and its inhibitory kinetics

Inhibition of alpha-glucosidases is recognised as an effective approach towards managing postprandial hyperglycaemia. This study aimed to identify a specific compound in Carya cathayensis Sarg. kernels (CCSKs) exhibiting strong inhibitory activities against alpha-glucosidase and elucidate the inhibitory kinetic mechanism. Employing a bioassay-guided approach, an alpha-glucosidase inhibitor was isolated from CCSKs through sequential chromatography protocol involving AB-8 macroporous adsorptive resin, Sephadex LH-20 and C-18-reversed phase silica gel. The resulting inhibitor was a novel tannin compound, identified as rugosin C ethyl ester. Rugosin C ethyl ester displayed superior inhibitory activity (IC50 of 2.60 mu g/mL) compared to acarbose (IC50 of 105.95 mu g/mL). The kinetic analysis indicated that rugosin C ethyl ester had a mixed-type reversible inhibition against alpha-glucosidase. The inhibition constants (K-i and K-is) were determined to be 3.119 and 0.856 mu g/mL, respectively. The findings indicated that rugosin C ethyl ester might serve as a promising functional ingredient in low-glycemic index foods.