Simulated Digestion and Metabolic Outcomes of <i>Tremella fuciformis</i> Polysaccharides and Their Effects on the Gut Microbiota

<i>Tremella fuciformis</i> polysaccharides (TFP) were evaluated for their gastrointestinal stability and microbiota-modulating effects using <i>in vitro</i> digestion and fecal fermentation. The results demonstrated that TFP possessed an average molecular weight of 2.21 × 10³ kDa, primarily composed of glucose (63.67%) and mannose (19.85%), and exhibited resistance to simulated gastrointestinal digestion. During fermentation, TFP was selectively metabolized by the gut microbiota. Compared with the blank control, TFP increased the Shannon index by 7.74% and significantly enhanced SCFA production, with acetate, propionate, and butyrate reaching 21.52, 8.62, and 4.60 mM at 24 h, respectively. TFP fermentation selectively promoted beneficial taxa, including <i>Megamonas</i> (28.3-fold), <i>Prevotella</i> (6.1-fold), and <i>Faecalibacterium</i> (2.4-fold). Correlation analysis revealed positive associations between SCFA production and specific bacterial genera, indicating that TFP supports a healthy gut environment. These findings establish TFP as a novel prebiotic candidate and highlight its translational potential for functional food formulations targeting gut microbiome modulation.