Abstract: To explore the lactic acid bacteria fermentation characteristics of Flammulina velutipes and its mechanism of assisting in reducing blood lipid, a compound lactic acid bacteria starter suitable for fermenting F. velutipes was screened from 8 kinds of lactic acid bacteria. Through establishing a hyperlipidemia mouse model and conducting a gavage experiment with fermented F. velutipes (FFV), its function and mechanism of assisting in reducing blood lipid were deeply investigated. The results showed that the FFV prepared with a compound lactic acid bacteria starter at a mass ratio of Lacticaseibacillus rhamnosus : Lactobacillus delbrueckii subsp. bulgaricus : Lactobacillus acidophilus = 2:3:1 had a sensory score of 84.60, a pH value of 3.36, a total acid production of 0.78 g/100g, and the viable count of lactic acid bacteria was 2.7×1010 CFU/mL. FFV could reduce the wet weight and index of the mouse liver and improve the antioxidant capacity of the liver. It could also significantly reduce the contents of serum total cholesterol (TC), triglyceride (TG), low - density lipoprotein cholesterol (LDL-C) and the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in hyperlipidemic mice, showing an auxiliary function in reducing blood lipid. FFV could significantly reduce the Firmicutes/Bacteroidetes ratio of the mouse gut microbiota and increase the relative abundances of Akkermansia, Faecalibacterium, Dubosiella, Lactobacillus, Bifidobacterium, Bacteroides, etc. to varying degrees, while reducing the contents of Helicobacter and Desulfovibrio. Moreover, the changes in the microbiota were correlated with the levels of serum lipids, transaminases, and liver oxidative stress. A total of 4354 metabolites belonging to 21 major categories were identified in the mouse gut contents, among which amino acids and their derivatives accounted for the largest proportion (39.98%). After being induced by a high - fat diet, the gut metabolites of mice changed significantly. FFV could improve the structural composition of gut metabolites in hyperlipidemic mice by regulating the contents of polypeptides, fatty acyls, organic acids, alkaloids, etc. produced by gut microbiota metabolism. This study confirmed that FFV has the effects of assisting in reducing blood lipid, regulating the gut microbiota and metabolites of mice, providing a theoretical basis for the development of functional foods from fermented F. velutipes.

Key words: Flammulina velutipes, lactic acid bacteria, fermentation characteristics, lowering blood lipids, gut microbiota, metabolites