Plant-based polysaccharides are increasingly recognized for their dual role as functional hydrocolloids and modulators of gut microbial ecology, yet a unified mechanistic understanding explaining how their structural features influence fermentability and host metabolic responses remains limited. Across a series of studies from our group involving polysaccharides isolated from date seeds, date pomace, date by-products, and carob (Ceratonia siliqua) pods, we systematically examined how compositional attributes (monosaccharide ratios, uronic acids, branching architecture), molecular weight distribution, and rheological behavior govern microbial selectivity, short-chain fatty acid (SCFA) production, and immune/metabolic outcomes. Together, these investigations establish an integrated structure–function framework for plant-derived hydrocolloids.

Polysaccharides obtained from these botanical sources consistently exhibited heteropolysaccharide profiles enriched in galacturonic acid, glucose, mannose, galactose, and fructose, with molecular weights spanning 100–300 kDa and polydispersity indices >2.0, indicative of structurally diverse fractions. Rheologically, all samples demonstrated dominant elastic behavior (G′ > G″), shear-thinning flow, and strong water-binding capacities—properties aligned with their hydrocolloid functionality. These structural and physicochemical characteristics directly shaped fermentability patterns and microbial niche utilization.

In vitro fecal fermentation revealed that specific structural motifs favored the enrichment of keystone bacterial taxa, including Bifidobacterium, Faecalibacterium, Blautia, Ruminococcus, and other fiber-degrading genera. Distinct structure-driven microbial shifts were observed: polysaccharides rich in uronic acids and with moderate molecular weight promoted butyrogenic pathways, whereas those with higher neutral sugars favored propionate-associated taxa. Across studies, fermentation consistently resulted in substantial production of acetate, propionate, and butyrate, with butyrate yields often exceeding standard references. Microbial functional prediction (KEGG, COG, MetaCyc) confirmed upregulation of carbohydrate metabolism, amino-acid pathways, and energy-related modules, supporting enhanced saccharolytic activity.

Ex vivo and in vivo investigations further validated these microbiota-mediated outcomes. Date byproduct polysaccharides improved intestinal immune stability and attenuated inflammatory responses through SCFA-dependent signaling, highlighting their systemic relevance. Across models, polysaccharide structure strongly predicted fermentation kinetics, SCFA profiles, microbiota reshaping, and downstream immunometabolic responses.

Collectively, the merged evidence demonstrates that the hydrocolloid behavior of plant-based polysaccharides—governed by their molecular architecture—directly influences their interaction with gut microbiota. This structure-guided microbial selectivity drives differential SCFA outputs that underpin their biological functions, including enhanced epithelial barrier function, immune modulation, and metabolic stability.