Structural Characterization, In Vitro Digestion, Fermentation Properties, and Impact on Gut Microbiota of Polysaccharide from Qingzhuan Tea

This study aimed to systematically evaluate the structural characteristics, digestive stability, and gut microbiota-modulating effects of a Qingzhuan tea polysaccharide fraction (QZTP3). Results showed that QZTP3 was an acidic heteropolysaccharide with a molecular weight of 1.35 × 105 Da, primarily composed of galacturonic acid, arabinose, galactose, and rhamnose in a molar ratio of 34.19:20.31:13.94:13.84. QZTP3 possesses a complex backbone with →4)-α-D-GalpA--(1→and→2,5)→α-L-Araf-(1→, among others, alongside side chains containing →3)-α-L-Araf-(1→ and →5)-α-L-Araf-(1→ units. Notably, QZTP3 demonstrated strong resistance to simulated gastrointestinal digestion. During in vitro fecal fermentation, QZTP3 stimulated the production of short-chain fatty acids, particularly acetate and propionate, which lowered pH. At the end of fermentation (48 h), the QZTP3 group exhibited higher relative abundances of beneficial genera (Bacteroides and Bifidobacterium) and lower relative abundances of putative pathogens (Escherichia-Shigella and Morganella). These findings support its potential application in functional foods and gut health supplements.