Release profile and metabolism of bound polyphenols of oat bran during <i>in vitro</i> simulated gastrointestinal digestion and colonic fermentation

Whole-grain foods have attracted emerging attention due to their health benefits. Whole grains are rich in bound polyphenols (BPs) linked with dietary fibers, which is largely underestimated compared with free polyphenols. In this study, <i>in vitro</i> simulated gastrointestinal digestion and colonic fermentation models were used to study the release profile and metabolism of BPs of oat bran. Significantly higher level of BPs was released during <i>in vitro</i> colon fermentation (3.05 mg GAE/g) than in gastrointestinal digestion (0.54 mg GAE/g). Five polyphenols were detected <i>via</i> LC-MS and their possible conversion pathways were speculated. Released BPs exhibited chemical antioxidant capacity. 16S rRNA sequencing further revealed that <i>Clostridium butyricum</i>, <i>Enterococcus faecalis</i>, <i>Bacteroides acidifaciens</i> were the key bacteria involved in the release of BPs, and this was verified by whole-cell transformation. Our results helped to explain the possible mechanism of the health benefits of BPs in whole grains.