Protease-producing lactic acid bacteria with antibacterial properties and their potential use in soybean meal fermentation

Background: As an adequate plant protein raw material, soybean meal has attracted extensive attention because of its high protein content, abundant amino acids essential for animals, and many functional nutrients. Feed fermentation is a new way to improve nutrient absorption of animals by inoculating microorganisms, which can also play a probiotic role. In order to screen the lactic acid bacteria with remarkable protease-producing performance and excellent growth and fermentation characteristics, 1000 strains isolated from different materials were evaluated in this study. After primary and re-screening, 22 strains both with protein transparent circle diameters larger than 15.00 mm (including the diameter of a hole puncher 10.00 mm) and enzyme activities greater than 20.0 U/mL were screened out for physiological and biochemical tests, as well as antimicrobial performance tests. Results: : Strains P (Pig) 15 and ZZUPF (Zhengzhou University Pig Fecal) 95, which have excellent physiological and biochemical characteristics, as well as good inhibition abilities for Staphylococcus aureus , Bacillus subtilis , Escherichia coli , Listeria monocytogenes , Pseudomonas aeruginosa , and Micrococcus luteus , were selected and used as fermenting agents for 3- and 30-day (d) fermentation of soybean meal. The analysis of microorganisms, fermentation quality, and chemical composition during fermentation revealed that all lactic acid bacteria addition groups had lower harmful bacteria and pH value, as well as higher lactic acid bacteria content and lactic acid level compared with CK and protease-treated groups. These effects were even better especially after 30 d of fermentation. Conclusions: : This study indicated that the selected strains Lactiplantibacillus plantarum subsp . plantarum P15 and Enterococcus faecalis ZZUPF95 could be considered as potential probiotics for fermenting soybean meal for further research.