Changes of Barley Bound Phenolics and Their Characteristics During Simulated Gastrointestinal Digestion and Colonic Fermentation In Vitro

Phenolic compounds in cereals, known for their biological activities, are primarily found in a bound state within the bran. Their changes during digestion are linked to physiological activities. In this study, the dynamic changes and fermentation characteristics of barley bound phenolics (BBPs) were investigated through an <i>in vitro</i> rat gastrointestinal digestion and colonic fermentation. UPLC-HRMS revealed that the release rate of BBPs during colonic fermentation was significantly higher than that during gastric digestion (0.13%) and intestinal digestion (0.43%), reaching 5.02%. After 48 h of colonic fermentation, gallic acid and ferulic acid accounted for 35.05% and 27.84% of the total released phenolic acids, respectively. Confocal microscopy confirmed that BBPs were predominantly released in the colon. Additionally, BBPs significantly increased the content of acetate during colonic fermentation compared to the control samples, correlating with a decrease in pH value. 16S rRNA sequencing further revealed the modulatory effects of BBPs on colonic microbiota structure: BBPs significantly enhanced the Chao1 and Shannon indices of the microbiota. Notably, BBPs inhibited the growth of potentially harmful bacteria such as <i>Proteobacteria</i> and <i>Enterobacteriaceae</i> while promoting the proliferation of beneficial bacteria such as <i>Akkermansia</i> and <i>Bifidobacteriaceae</i>, thereby modulating the structure of the gut microbial community. These findings suggested that BBPs may promote gut health through prebiotic activity in the colon.