Deep Eutectic Solvent-Based Extraction Optimization, Structural Characterization, and Alleviating Effects of Tremella fuciformis Polysaccharides on Ulcerative Colitis

polysaccharides (TFPS) exhibit anti-inflammatory and gut-microbiota-modulating activities, but conventional extraction methods often show limited efficiency and may affect polysaccharide structural integrity. This study optimized a deep eutectic solvent (DES)-based extraction method with potential environmental advantages for TFPS, characterized the major purified fraction, and evaluated its effects in a dextran sulfate sodium (DSS)-induced experimental colitis model. Extraction parameters for the choline chloride-lactic acid DES system were refined through single-factor testing combined with response surface methodology. The purified fraction TFPS-1 was characterized by chromatographic, spectroscopic, methylation, and NMR analyses, and its biological effects were assessed in DSS-treated mice. Under the optimized conditions, the TFPS yield reached 33.09 ± 1.52%, representing a 77.6% increase compared with hot-water extraction. TFPS-1 was identified as a low-molecular-weight glucan mainly containing α-(1→4)- and β-(1→6)-linked glucose residues. In experimental colitis mice, TFPS-1 alleviated body weight loss, colon shortening, and histopathological injury; increased mucus secretion and barrier-related gene expression; reduced pro-inflammatory cytokines; increased IL-10; and partially adjusted gut microbiota composition. These results indicate that DES-based extraction is an efficient strategy for preparing TFPS and provide evidence that TFPS-1 may be further explored as a food-derived polysaccharide ingredient for intestinal protection in experimental colitis-related contexts.