Optimized Extraction of Soluble Dietary Fiber from Lyophyllum decastes and Its Effect on Hypolipidemic and Gut Microbiota in Mice

Lyophyllum decastes soluble dietary fiber (LDSDF) is a polysaccharide-based active ingredient derived from the edible and medicinal fungus L. decastes. However, its extraction methods remain unoptimized, and its hypolipidemic and gut microbiota effects have yet to be thoroughly investigated in mice. In this study, response surface optimization of the LDSDF extraction method indicated an optimal extraction temperature of 99 °C, a solid/liquid ratio of 25:1 mL/g, and an extraction time of 1.9 h. The optimal ethanol precipitation parameters were a concentration ratio of 3.9, an ethanol concentration of 74.4%, and a precipitation time of 16.4 h. These conditions afforded an LDSDF yield of 15.83%. Following 6 weeks of oral gavage of LDSDF in obese mice, the results showed that LDSDF inhibited increases in body and organ weight; reduced serum levels of total cholesterol, triglycerides, and low-density lipoprotein cholesterol; increased serum levels of high-density lipoprotein cholesterol; decreased alanine aminotransferase and aspartate aminotransferase activities; and lowered systemic levels of pro-inflammatory cytokines (tumor necrosis factor-α, interleukin-6, and interleukin-1β). Concurrently, it elevated the hepatic activities of superoxide dismutase, catalase, and glutathione peroxidase; reduced malondialdehyde levels; and mitigated lesions in liver and epididymal fat cells. Meanwhile, 16S rRNA sequencing revealed that LDSDF significantly alleviated intestinal flora imbalances. Overall, this study established an optimized extraction process to obtain LDSDF with a high yield and confirmed the hypolipidemic and gut microbiota-modulating efficacy of this active ingredient, highlighting its potential for use as a functional food ingredient.