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

This study investigated the optimal conditions for enhancing protein quality and reducing anti-nutritional factors in soybean meal (SBM) through solid-state fermentation (SSF) with Bacillus. Among 78 isolates, strain MH03 exhibited the highest extracellular enzyme production and efficacy in enhancing SBM quality. 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 anti-nutritional compounds, including glycinin, β-conglycinin, trypsin inhibitor, and oligosaccharides. Crude protein content increased from 47.89±0.07 % to 55.84±0.25 %, with protein solubility increased from 74.96±0.45 % to 90.54±0.28 %, with statistically significant increases. Other nutritional values were also significantly enhanced. Essential amino acids, such as valine, methionine, isoleucine, and lysine also increased. Based on 16S rRNA gene sequencing, MH03 was identified as Bacillus siamensis. These findings highlight the potential of B. siamensis MH03-fermented SBM as a high-quality protein ingredient for animal feed applications.