Hydrothermal treatment improves xanthine oxidase inhibitory activity and affects the polyphenol profile of Flos Sophorae Immaturus

BACKGROUND Flos Sophorae Immaturus (FSI) is rich in polyphenols and a potential uric acid‐lowering food. However, the processing of FSI is greatly restricted due to the heat sensitivity and low solubility of polyphenols. In this study, hydrothermal treatment – an effective strategy – was applied to FSI processing. The variation of xanthine oxidase (XO) inhibitory effect and polyphenol composition of FSI during hydrothermal treatment were recorded. RESULTS The XO inhibition rate of FSI increased from 32.42% to 89.00% after hydrothermal treatment at 220 °C for 30 min, as well as total polyphenols (from 0.66 to 1.11 mg mL−1) and flavonoids (from 1.21 to 1.58 mg mL−1). However, high thermal temperature (>160 °C) and extended thermal time (>90 min) caused the degradation of polyphenols. Rutin, kaempferol‐3‐O‐rutinoside and narcissoside rapidly degraded and converted to quercetin, kaempferol and isorhamnetin when the temperature exceeded 160 °C. The maximum yields of quercetin, kaempferol and isorhamnetin were at 220 °C for 30 min, 90 min and 90 min, respectively. Meanwhile, the conversion kinetics conformed to the first‐order model. Interestingly, these newly formed polyphenols possessed better XO inhibitory effects than their derivatives with 3‐O‐rutinoside. CONCLUSION Polyphenol conversion during hydrothermal treatment was the main reason for enhancing XO inhibitory activity. Therefore, hydrothermal treatment is an appropriate method for improving the XO inhibitory effect of FSI. © 2022 Society of Chemical Industry.