In vitro inhibitory effects of polyphenols from Tartary buckwheat on xanthine oxidase: Identification, inhibitory activity, and action mechanism

•Eight primary polyphenols were identified and quantified in Tartary buckwheat.•Five xanthine oxidase inhibitors were verified in Tartary buckwheat.•Quercetin made a considerable contribution (77.63%) to the inhibitory effect.•Kaempferol-quercetin complex revealed a sub-additive inhibitory effect. The xanthine oxidase (XO) inhibitory activity is an important way to evaluate the anti-hyperuricemia effect of natural products. In the present work, the XO inhibitory effect of Tartary buckwheat was elucidated by polyphenols determination, omission experiment, interaction assay, inhibition types, fluorescence spectroscopy, and molecular docking. The results revealed that eight primary polyphenols were identified, including rutin (544 mg/100 g) and quercetin (261 mg/100 g). Quercetin (IC50 = 0.03 mg/mL) was a mixed-type inhibitor and exhibited the strongest inhibitory effect, followed by kaempferol (IC50 = 0.11 mg/mL). Moreover, a sub-additive effect was exhibited in the complex of quercetin-kaempferol, but the combination of quercetin and other polyphenols caused interference or antagonism effects. Furthermore, quercetin and kaempferol showed an obvious fluorescence quenching effect on XO, and the bindings were mainly driven by hydrophobic forces and hydrogen bonds. This study shows that Tartary buckwheat may be a potential functional food to inhibit XO activity.