Glycosidic linkage-dependent fermentation of polysaccharide mixtures by human gut microbiota in vitro

Dietary polysaccharides that escape digestion in the upper gastrointestinal tract are key modulators of gut microbiota composition and metabolic activity, with potential relevance to host health and gut-brain signaling. However, the mechanisms of specific glycosidic architectures within polysaccharide mixtures govern microbial succession remain undisclosed. In vitro fecal fermentation was used to compare a structurally heterogeneous pine nut skin fraction (Et75), enriched in pectic polysaccharides, xyloglucans, and type-II arabinogalactans, with a commercial fructan and the insoluble pine nut skin matrix. Glycosidic-linkage depletion, pH, and short-chain fatty acid production were monitored during fermentation and microbiota composition assessed after 24 h. Et75 underwent rapid, linkage-dependent fermentation, with preferential early consumption of xyloglucan-associated residues and slower depletion of pectic and arabinogalactan motifs. This hierarchical utilization was accompanied by a selective shift toward Bifidobacterium adolescentis and other saccharolytic and cross-feeding taxa, yielding a community response comparable to fructans but mechanistically distinct in substrate selectivity. In contrast, insoluble pine nut skin matrix was poorly fermented. Fructans also promoted B. adolescentis and rapid short-chain fatty acid production, with donor-dependent inulin depolymerization driven by Prevotella copri. Glycosidic-linkage composition is key determinant of polysaccharide fermentation and support structurally defined mixtures as promising prebiotic substrates with relevance for psychobiotic-oriented studies.