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

Summary Inhibition of α-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 α-glucosidase and elucidate the inhibitory kinetic mechanism. Employing a bioassay-guided approach, an α-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 (IC 50 of 2.60 μg/mL) compared to acarbose (IC 50 of 105.95 μg/mL). The kinetic analysis indicated that rugosin C ethyl ester had a mixed-type reversible inhibition against α-glucosidase. The inhibition constants ( K i and K is ) were determined to be 3.119 and 0.856 μg/mL, respectively. The findings indicated that rugosin C ethyl ester might serve as a promising functional ingredient in low-glycemic index foods.