Effects of Ganoderma lucidum fermentation on the structure of Tartary buckwheat polysaccharide and its impact on gut microbiota composition

Fermentation modifies plant polysaccharides and enhances their bioactivity. In this study, polysaccharides were extracted from Ganoderma lucidum-fermented (FBP) and non-fermented (NBP) Tartary buckwheat. The structure of the polysaccharides and their effects on gut microbial composition were explored. According to the results, the molecular weight of FBP lowered from 8.86 x 105 Da to 3.83 x 104 Da, the fermentation process produced fucose (7.72 %) and mannose (6.68 %), and the content of glucose and galactose increased. Compared with NBP, FBP showed a significant increase in solubility, crystallinity and thermal stability, while there was a decrease in apparent viscosity. The in vitro fecal fermentation results suggested that FBP promoted the production of shortchain fatty acids, with acetic acid, propionic acid and butyric acid being the main metabolites. FBP and NBP dramatically decreased the relative abundance of Escherichia-Shigella. FBP increased the relative abundances of Bacteroides, Parabacteroides, and Megamonas, while NBP increased those of Bifidobacterium and Phascolarctobacterium. Finally, further analysis of functional prediction indicated that carbohydrate metabolism, lipid metabolism and cardiovascular disease were the most vital pathways for FBP to promote health. This study offers some theoretical foundation for the chemical structure and regulation of gut microbiota by Ganoderma lucidum fermented buckwheat modified polysaccharides.