Comparison of α-amylase, α-glucosidase and lipase inhibitory activity of the phenolic substances in two black legumes of different genera.

Antioxidant-rich plant foods can inhibit starch and lipid digestions that are relevant to diabetes management. Two high-antioxidant black legumes, black soybean (Glycine max) and black turtle bean (Phaseolus vulgaris), belonging to two different genera were used to investigate their capacity against digestive enzymes. Phenolic substances were compared in crude, semi-purified extracts (semi-purified by XAD-7 column), and fractions (fractionationed by Sephadex LH-20 column) from these two legumes. In addition, their antioxidant capacities and abilities to inhibit digestive enzymes were characterized. Results showed that Fraction V from black soybean was the most effective (IC50: 0.25mg/mL) against α-amylase; Fraction V from black turtle bean was the most potent (IC50: 0.25μg/mL) against α-glucosidase; Fraction IV from black turtle bean was the most powerful (IC50: 76μg/mL) against lipase. Of the pure phenolic compounds tested, myricetin showed the highest inhibition of α-amylase, α-glucosidase and lipase (IC50: 0.38mg/mL, 0.87μg/mL and 15μg/mL, respectively).