Regulating Effects of Three Polysaccharides on Gut Microbiota in Felines and Canines: Insights from <i>In Vitro</i> Digestion, Fecal Fermentation, and Lactic Acid Bacterial Fermentation

This study evaluated the effects of laminaria polysaccharide (FU), aloe polysaccharide (AL), and yeast β-glucan (YG) on in vitro digestion, fecal fermentation, and lactic acid bacterial fermentation in felines and canines. FU (Mw 27 713 g/mol), AL (44 425 g/mol), and YG (29 296 g/mol) were primarily composed of glucose, galacturonic acid, and glucuronic acid. The FU strongly promoted the fermentation of <i>Bifidobacterium</i>, <i>Lactobacillus</i>, and <i>Pediococcus</i>. The AL slightly supported <i>Lactobacillus</i>. The YG showed minimal activity. Molecular weights decreased after digestion with negligible monosaccharide release. The FU and AL were almost completely metabolized during fecal fermentation, while YG had ∼50% utilization. The FU produced the highest lactate concentration. The YG significantly increased SCFA levels, especially in canines, surpassing fructooligosaccharides. The FU:AL:YG mixture (0.8:0.2:1, FAY) achieved the best overall effects. 16S rRNA analysis revealed the enrichment of SCFA-producing genera (e.g., <i>Megamonas</i>, <i>Parabacteroides</i>) and suppression of odor-related bacteria (e.g., <i>Fusobacterium</i>, <i>Desulfovibrio</i>). Metabolomics showed reduced levels of odor compounds (e.g., 2-oxindole, 5-hydroxyindole) and increased secondary bile acids (e.g., deoxycholic acid, glycocholic acid). The FU, AL, and FAY upregulated bile secretion, neuroactive pathways, and arachidonic acid metabolism, while YG activated the ABC transporter pathway.