Bioconversion of soybean meal into gut microbiota-targeting polysaccharides via fermentation by Bacillus subtilis

Understanding the internal laws of probiotic solid-state fermentation is important for improving the nutritional composition and utilization of soybean meal (SBM). The present study aims to investigate the mechanism of SBM solid-state fermented by Bacillus subtilis over a 24 h period. The microstructure of the SBM was decomposed during fermentation. Post fermentation, the cellulose and hemicellulose content were significantly reduced by 38.83% and 22.24%, and the concentrations of small peptides and amino acids remarkably increased to 12.11% and 41.90%, respectively (P < 0.05). Notably, the results of transcriptome and enzyme activity highlighted that endo-1,4-β-xylanase, endoglucanase and β-1,4-mannan endonuclease were significantly synthesized and played critical roles in fiber degradation during fermentation. Additionally, the polysaccharides of SBM and fermented soybean meal (FSBM) were extracted and characterized, and it was found that the polysaccharide structures of FSBM were significantly different compared to pre-fermentation. The in vitro fermentation results of polysaccharides further indicated that fermented soybean meal polysaccharides (FSPS) dramatically promoted the abundance of porcine gut commensal Bifidobacterium and Lactobacillus, and enhance the microbial functions of fructose and mannose metabolism. These findings elucidate the microbial genomic mechanism during fermentation to reveal the potential regulatory effects of FSPS on gut microbiota and expand the utilization of SBM.