Quality improvement of soybean meal by simultaneous microbial fermentation and enzymolysis and untargeted metabolomic analysis of its metabolites

Twelve lactobacillus strains, four yeast strains, and eight proteases were screened, and their effects on oligosaccharide degradation, lactic acid production, and proteolytic capacity were investigated in soybean meal. The simultaneous microbial fermentation and enzymolysis (SMFE) conditions were optimized as feed/water ratio of 1:0.8 (w/v), yeast inoculum of 2.1×105 CFU/g, lactobacillus inoculum of 2.1×107 CFU/g, protease addition of 200 U/g, and fermentation at 37 °C for 48 h. The results showed that SMFE soybean meal exhibited superior performance over unprocessed soybean meal, showing increases in crude protein content from 49.8% to 56.3%, acid-soluble protein content from 3.7% to 10.4%, lactic acid production from 0 to 71.5 g/kg, and a decrease in oligosaccharide content from 6.4% to 0%. The comprehensive performance of SMFE soybean meal is higher than that from enzymolysis or fermentation alone Non-targeted metabolomic analysis revealed a diversity of metabolites in fermented soybean meal produced by different processes, and 8366 detected metabolites were mainly amino acids and their metabolites. Furthermore, among the six experimental groups, the metabolites of the SMFE group, and the yeast and lactic acid bacteria fermentation groups were the most similar. This study facilitates the assessment of overall quality of soybean meal and reveals the superiority of SMFE over traditional methods in enhancing nutritional profile of soybean meal.