Inhibition of Starch-Digesting Enzymes by Rutin and Quercetin in Tartary Buckwheat

A variety of spectroscopic techniques were used to study the inhibitory effect and mechanism of rutin and quercetin on starch-digesting enzymes and their combined effect. The results showed that the types of inhibition of rutin and quercetin on α-amylase were competitive, mainly driven by hydrophobic interactions and hydrogen bonds, and the half maximum inhibitory concentrations (IC₅₀) were 0.36 and 0.22 mg/mL, respectively. The inhibition of α-glucosidase by rutin and quercetin was of mixed type, driven by hydrogen bonds, and the IC₅₀ were 1.30 and 0.362 mg/mL, respectively. Moreover, both flavonoids could combine with α-amylase and α-glucosidase at only one/kind of action site to form a complex, thus inhibiting the activity of the enzymes, and their combinations in different proportions had a synergistic inhibitory effect on α-amylase and α-glucosidase. When the concentration ratio between rutin and quercetin was 7:1 and 3.6:18, the combination index for α-amylase and α-glucosidase was 0.20 and 0.22, respectively, showing the best synergistic inhibitory effect. This study provides a theoretical basis for further research on the interaction mechanism between flavonoids and starch-digesting enzymes, is meaningful for guiding the processing and utilization of edible and medicinal plants rich in flavonoids, and helps to promote the virtuous cycle of the tartary buckwheat industry.