Bacillus velezensis DP-2 isolated from Douchi and its application in soybean meal fermentation

Soybean meal (SBM) is the most common protein source used in the poultry and livestock industries. It has high-quality protein, an excellent amino acid (AA) profile, and positive isoflavone properties. However, the antigen proteins in SBM are unsuitable for young animals. The objective of this study was to identify a Bacillus strain that can degrade soybean antigen proteins, and to evaluate the feasibility of its application in SBM fermentation.

Bacillus velezensis DP-2 was isolated from Douchi, a fermented Chinese food. It degraded 96.14% and 66.51% of glycinin and β-conglycinin, and increased the trichloroacetic acid-soluble protein (TCAN) content by 5.46 times in the SBM medium. DP-2 could secrete alkaline protease and neutral protease, with productivities of 5.85 and 5.99 U mL^-1 . It had broad-spectrum, antibacterial activities against Rhizopus nigricans HR, Fusarium oxysporum ACCC37404, Penicillium digitatum SQ2, Aspergillus flavus C1, Aspergillus niger ACCC30005, Trichoderma viride YZ1, Candida tropicalis CICC1630, and Salmonella sp. ZY. For SBM fermentation, the optimal inoculum rate, temperature, and fermentation time of DP-2 were 2.21 × 10⁷ CFU g^-1 , 37 °C, and 48 h, respectively. The fermented soybean meal (FSBM) was cream-colored and glutinous. Its crude protein (CP), soluble protein, and TCA-N content were improved by 13.45%, 12.53%, and 6.37 times, respectively. The glycinin and β-conglycinin content were reduced by 78.00% and 43.07%, respectively, compared with raw SBM.

Bacillus velezensis DP-2 has potential as a starter culture for SBM fermentation. © 2020 Society of Chemical Industry.