Organic acid‐assisted heat treatment enhances the xanthine oxidase inhibitory activity of <i>Flos Sophorae Immaturus</i> tea

Abundant polyphenols in Flos Sophorae Immaturus tea (FSIt) exhibited xanthine oxidase (XO) inhibitory activity. However, the XO inhibitory activity of FSIt was closely related to the processing methods. Herein, organic acids were employed as catalysts for polyphenol conversion during heat treatment and applied to enhance the XO inhibitory activity of FSIt; the potential mechanisms were clarified by polyphenols degradation and conversion analysis, omission experiment, and interaction assay. Results showed that 10% oxalic acid (OA)- or 10% lactic acid (LA)-assisted heat treatment significantly increased the XO inhibition rate from 26.49% to 84.16% and 75.45%, respectively. OA-assisted presented the high catalytic efficiency of rutin (31.56%), hyperoside (33.21%), and quercitrin (34.14%) to quercetin during heat treatment, as well as kaempferol-3-O-rutinoside (20.04%) to kaempferol and narcissoside (26.04%) to isorhamnetin. The de-glycosylation of polyphenols was the predominant reason for the enhancement of XO inhibitory activity. Moreover, the synergistic effect of chlorogenic acid and flavonoids also exhibited the ability to improve the XO inhibitory activity of FSIt. PRACTICAL APPLICATION: Improving the polyphenol composition of FSIt through organic acid-assisted heat treatment, thereby enhancing its XO inhibitory activity, is a promising approach to deeply understand the relationship between processing methods and bioactivities of products, and further promote innovation in specific functional food processing technology.