Improvement of soybean meal quality by one-step fermentation with mixed-culture based on protease activity

Microbial fermentation can improve the quality of soybean meal by reducing the level of anti-nutrition factors and increasing the content of protein and small peptides. In this study, Bacillus velezensis, Enterococcus faecium and Saccharomyces boulardii were used for one-step mixed fermentation of soybean meal. The fermentation of soybean meal was carried out in an anaerobic bag using fermentation liquid of strains with maximum protease activity as inoculum and water. The results of process optimization showed that the mixture ratio of B. velezensis: E. faecium: S. boulardii was 37.5%:25%:37.5%. The three microorganisms added together as a mixture. Under the conditions of 55% inoculation with microorganisms mixture, 0.8% acid protease addition, 46 ℃ and 6 days, the quality of fermented soybean meal was significantly improved. The small peptides increased from 4.48% to 47.4%, the TCA solution protein increased from 44.3 g/kg to 255.2 g/kg, the antigenic protein glycinin decreased by 94.37% from 320.12 μg/mL to 18.02 μg/mL, and β-conglycinin decreased by 85.83% from 232.11 μg/mL to 32.89 μg/mL. Other anti-nutritional factors urease, phytic acid and stachystryose all decreased. The result indicated that it was feasible to improve the feed quality of soybean meal by one-step mixed fermentation based on protease activity. Fermentation is the main method to improve the feed quality of soybean meal. Our study revealed that one-step mixed-culture fermentation based on microbial protease activity showed a significant effect on increasing beneficial small peptides, reducing anti-nutrient factors and enhancing palatability of soybean meal. This process simplified the operation of mixed fermentation and could be implemented in solid fermentation system of feed and food industry to improve the beneficial properties of products.