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

Lithocarpus litseifolius [Hance] Chun (L. litseifolius), 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 in vitro digestion bioactivities of special-grade polysaccharides (STPs) and first-grade polysaccharides (FTPs) from L. litseifolius green tea, alongside their modulatory effects on the gut microbiota following in vitro fermentation. The results demonstrated that STPs exhibited higher total carbohydrate and uronic acid content, higher molecular weight, and greater in vitro bioactivity compared to FTPs, despite structural similarities. During in vitro 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 Firmicutes and Bacteroidota. Concurrently, a marked increase in short-chain fatty acid (SCFA) output—particularly acetate and propionate—was observed. STPs primarily enriched Actinobacteria, whereas FTPs favored Bacteroidota, both contributing to elevated acetate and propionate levels while suppressing potential pathogens such as Proteobacteria and Escherichia–Shigella. These findings underscore the potential of L. litseifolius green tea polysaccharides to serve as effective prebiotics for gut microbiota modulation.