Selection of proteolytic LAB starter cultures for acidification of soy based dairy alternatives

Strains isolated from different environments in Denmark (plant, fermented food, dairy and animal faeces) were investigated for their capacity to produce a curd upon fermentation of Soy Based Milk Alternative (SBMA). Acidification dynamic was determined in commercial SBMA at 30 °C and production of metabolites was investigated by HPLC analysis. Proteomics was used to determine the hydrolysis profile for individual soy proteins. SBMA samples fermented with selected strains were characterized with rheology and the genome sequence was analysed. From an initial selection of 61 strains, 29 (5 Lactococcus lactis, 4 Lactiplantibacillus plantarum, 6 Leuconostoc mesenteroides, 3 Leuconostoc pseudomesenteroides, 1 Leuconostoc citreum, 1 Leuconostoc lactis, 6 Lactobacillus, 2 Pediococcus pentosaceus and 1 Weissella) were found to acidify SBMA, with final pH ranging from 4.46 to 6.07. Lactic acid concentration ranged from 1.8 mg/mL to 4.3 mg/mL. Two strains of L. lactis and three of Ln. pseudomesenteroides showed proteolytic activity in soy, and proteolysis patterns of glycinin G4 (UniProtKB: P02858) and β-conglycinin α subunit (P0DO15/P0DO16) were investigated further in depth. They were the only investigated strains presenting a PrtP sequence in their genomes. In view of these results, these five strains are candidates of particular interest to produce a soy-based yogurt-like product.