Introducing Bacillus natto and Propionibacterium shermanii into soymilk fermentation: A promising strategy for quality improvement and bioactive peptide production during in vitro digestion

Herein, the texture properties, polyphenol contents, and in vitro protein digestion characteristics of soymilk single- or co-fermented by non-typical milk fermenter Bacillus natto (B. natto), Propionibacterium freudenreichii subsp. shermanii (P. shermanii), and traditional milk fermenter were evaluated. Co-fermenting procedure containing B. natto or P. shermanii could raise the amounts of gallic acid, caffeic acid, and GABA when compared to the unfermented soymilk. Co-fermented soymilk has higher in vitro protein digestibility and nutritional protein quality. Through peptidomic analysis, the co-work of P. shermanii and Lactobacillus plantarum (L. plantarum) may release the highest relative percentage of bioactive peptides, while the intervention of B. natto and Streptococcus thermophilus (S. thermophilus) resulted in more differentiated peptides. The multi-functional bioactive peptides were mainly released from glycine-rich protein, β-conglycinin alpha subunit 1, and ACB domain-containing protein. These findings indicated the potential usage of B. natto/S. thermophilus or P. shermanii/L. plantarum in bio-enhanced soymilk fermentation.