Active substances and in vitro anti-diabetic effects of a traditional folk remedy Bian-Que Triple-Bean Soup as affected by the boiling time.

Bian-Que Triple-Bean Soup (Bian-Que San Dou Yin in Chinese) is a folk remedy which has been used for thousands of years in the practices of traditional Chinese medicine. The objectives of the current study were aimed to determine in vitro anti-diabetic effects and to find out the optimal cooking time for retaining active substances. α-Glycosidase in vitro inhibitory capacities and DPPH free radical scavenging capacities, and contents of active substances including total phenolics, saponin, tannin and monomeric anthocyanin, were determined with colorimetric methods. The results revealed that Bian-Que Triple-Bean Soup boiled for 30 min has the most effective impact on α-glycosidase inhibition. n-Butanol-soluble and water extract fractions showed relatively higher α-glycosidase inhibitory activity (17.4% and 11.2%, respectively) than that (2.56% and 5.32%, respectively) of hexane-soluble and dichloromethane-soluble fractions. Degradation was observed for those thermally unstable substances (TPC, tannin, and anthocyanin) by extending the boiling time; however, there were no obvious changes for thermo-stable substances (saponin).