Bioaccessibility of Phenolic Compounds in Green Citrus Syrup During Simulated Gastrointestinal Digestion and Their Relation to Antioxidant Activity and Xanthine Oxidase Inhibition

Abstract

Background:Green citrus is rich in phenolic compounds with potential antioxidant and xanthine oxidase (XO) inhibitory activities. However, the dynamic changes in its free and bound phenolic fractions during gastrointestinal digestion remain unclear.Methods:Green citrus syrup was subjected to in vitro simulated gastrointestinal digestion. Free and bound phenolic compounds were extracted at different digestion stages, and phenolic content, phenolic composition, bioaccessibility, antioxidant activity, and XO inhibitory activity were evaluated. Spearman correlation analysis and molecular docking were further performed to identify potential phenolic contributors to XO inhibition.Results:Simulated digestion markedly increased free phenolic content from 522.2 mg gallic acid equivalents (GAE)/L before digestion to 800.7 mg GAE/L after gastric digestion and 859.5 mg GAE/L after intestinal digestion. In contrast, whereas bound phenolic content decreased from 429.6 to 54.1 mg GAE/L. A total of 28 free and 21 bound phenolic compounds were identified. Phenolic bioaccessibility increased from 55.09% to 89.85% during digestion, accompanied by enhanced antioxidant activity and XO inhibitory activity. Correlation analysis identified 20 phenolic compounds positively associated with XO inhibition, and molecular docking suggested that hesperidin, naringin, hesperetin, hesperetin 7-O-glucoside, morin, and 6-gingerol could interact with XO mainly through hydrogen bonding.Conclusions:In vitro gastrointestinal digestion promoted the release and bioaccessibility of green citrus phenolics, thereby enhancing the associated antioxidant and XO inhibitory capacities. These findings provide a basis for the functional development and processing of green citrus syrup.