Improvement of protein quality and reduction of anti-nutritional factors in soybean meal by solid-state fermentation with Bacillus siamensis MH03

This study aimed to investigate the optimal conditions for improving protein quality and reducing anti-nutritional factors through solid-state fermentation (SSF) using selected Bacillus strains. From screening of 78 isolates, strain MH03 exhibited the highest extracellular enzyme production, protein digestion and reduction of anti-nutrients in soybean meal (SBM). Under optimized SSF conditions of 5 kg SBM, 5 cm thickness and 50% initial moisture for 72 h, strain MH03 increased soluble protein from 3.31±0.21 to 10.16±0.27 g/100 g and significantly reduced glycinin, β-conglycinin, trypsin inhibitor, and oligosaccharides. Crude protein content reached 55.84±0.25%, with protein solubility improving to 90.54±0.28%. Other nutritional values were also significantly enhanced and essential amino acids, including valine, methionine, isoleucine, and lysine also increased. Based on 16S rRNA gene sequencing, MH03 was identified as Bacillus siamensis. These results demonstrate the potential of SBM fermented with B. siamensis MH03 as a high-quality protein source for animal feed application.