The most abundant polyphenol of soy leaves, coumestrol, displays potent α-glucosidase inhibitory activity

► Coumestrol shows the most potent α-glucosidase inhibition of all soy bean leaf extracts. ► Coumestrol starts to accumulate in soybean leaves from 84 days after sowing. ► A new α-glucosidase inhibitor, Glyceollin V was isolated from soybean leaves.