<i>In vitro</i> simulated digestion and fermentation of <i>Lithocarpus litseifolius</i> [Hance] Chun green tea polysaccharides and their modulation of the gut microbiota

<i>Lithocarpus litseifolius</i> [Hance] Chun (<i>L. litseifolius</i>), a herbal tea rich in bioactive polysaccharides, has garnered attention for its health-promoting potential. Polysaccharides represent its principal bioactive component and play a significant role in regulating the gut microbiota. This study investigated the physicochemical characteristics and <i>in vitro</i> digestion bioactivities of special-grade polysaccharides (STPs) and first-grade polysaccharides (FTPs) from <i>L. litseifolius</i> green tea, alongside their modulatory effects on the gut microbiota following <i>in vitro</i> fermentation. The results demonstrated that STPs exhibited higher total carbohydrate and uronic acid content, higher molecular weight, and greater <i>in vitro</i> bioactivity compared to FTPs, despite structural similarities. During <i>in vitro</i> simulated digestion, polysaccharides underwent moderate physicochemical modifications accompanied by partial loss of bioactivity. Notably, STPs exhibited a greater extent of degradation compared to FTPs. Despite differential digestion-induced degradation, most STPs and FTPs remained largely intact upon reaching the colon and were thus accessible to the gut microbiota for fermentation. Fecal fermentation demonstrated efficient microbial utilization of STPs and FTPs, each modulating the architecture of the human gut microbiota, characterized by carbohydrate consumption, a decrease in pH, and an elevated relative abundance of beneficial bacterial phyla, including <i>Firmicutes</i> and <i>Bacteroidota.</i> Concurrently, a marked increase in short-chain fatty acid (SCFA) output-particularly acetate and propionate-was observed. STPs primarily enriched <i>Actinobacteria</i>, whereas FTPs favored <i>Bacteroidota</i>, both contributing to elevated acetate and propionate levels while suppressing potential pathogens such as <i>Proteobacteria</i> and <i>Escherichia</i>-<i>Shigella</i>. These findings underscore the potential of <i>L. litseifolius</i> green tea polysaccharides to serve as effective prebiotics for gut microbiota modulation.