Poly-γ-glutamic acid-producing Bacillus velezensis fermentation can improve the feed properties of soybean meal

Soybean meal (SBM), a high-protein animal feed, contains several anti-nutritional factors, which limit its utilization. Poly-γ-glutamic acid (γ-PGA), a biological macromolecule, can significantly improve the health and growth benefits of animal feed. However, there are rare reports about SBM fermentation with γ-PGA-producing bacteria to improve its nutritional quality. In this study, we isolated a glutamic acid-independent poly γ-glutamic acid (γ-PGA) producing Bacillus velezensis SCP024–S-4 bacterial strain and used it for solid fermentation of SBM. The results showed that the maximum γ-PGA yield in fermented soybean meal (FSBM) reached up to 89.64 g/kg without adding glutamic acid. Meanwhile, the content of proteins, free amino acids and small peptides increased by 12.83%, 347.96 μg/g and 108.11 mg/g, respectively. Soy globulin, β-conglutinin and trypsin inhibitor all decreased below 3 mg/g. Mice were fed with CK (control diet), SBM and FSBM respectively. The average daily food intake in the FSBM, SBM, and CK groups were 7.68, 5.25, and 6.36 g, respectively. Compared with the CK group, the mice weight growth rate was significantly higher in the FSBM group. Mice blood and spleen tests showed no negative effect of FSBM. The high-throughput sequencing of mice intestinal microflora indicated that FSBM increased the richness of intestinal microbiota; especially, the types and quantities of Lactobacillus were significantly increased. This study provides a feasible strategy to improve the nutritional quality of SBM as an animal feed.