Gut microbiota modulation, short-chain fatty acid (SCFA) production, and immune responses associated with structurally distinct peach pectin fractions.

Peach pectin is a promising functional polysaccharide, yet the structure-activity associations among its fractions remain poorly defined. Here, four structurally distinct peach pectin fractions, water-soluble (WSP), chelator-soluble (CSP), sodium carbonate-soluble (SSP), and an enzymatically modified fraction (ES) with targeted homogalacturonan fragmentation, were evaluated in cyclophosphamide-induced immunosuppressed female mice. Among them, SSP exerted the most comprehensive benefits. Specifically, SSP treatment restored cytokine balance; increased red blood cell count and hemoglobin levels by 24.56% and 34.39%, respectively, relative to the model group; enhanced microbial diversity (Shannon and Sobs indices increased by 21.17% and 12.05%, respectively); and optimized short-chain fatty acid profiles. These effects were strongly associated with SSP's structural traits, particularly moderate branching, higher rhamnogalacturonan I (RG-I) content, and characteristic monosaccharide composition. Correlation analysis identified taxon-specific responses, where norank_f_UCG-010 (unclassified genus) was correlated with the RG-I index (r = 0.99) and arabinose (r = 0.99), and Blautia, Enterorhabdus, and Eubacterium_brachy_group (unclassified genus) with rhamnose, fucose, and galactose, respectively. Higher branching was negatively correlated with Bacillus (r = -0.95) and norank_f_Desulfovibrionaceae (unclassified genus) (r = -0.99) and positively correlated with valeric acid levels (r = 0.96). Overall, structural differences of the peach pectin fractions were related to the differences in the modulation of the microbiota and the immune response in this model, highlighting SSP as a promising functional ingredient.