Characterization of fermented soymilk by Schleiferilactobacillus harbinensis M1, based on the whole-genome sequence and corresponding phenotypes

The use of Schleiferilactobacillus (S.) harbinensis M1 as a starter culture, has been shown to improve the organoleptic quality of fermented soymilk, but its contribution to nutrient transformation and health-related functionality remains unclear. This study characterized the biotransformation of carbohydrates, isoflavones, proteins and free amino acids, as well as the antioxidant and antiproliferative activities of soymilk fermented by S. harbinensis M1. After fermentation, soybean carbohydrates were mainly converted into lactic acid (76.68 mmol/L) and acetic acid (8.19 mmol/L), isoflavone glucosides (daidzin and genistin) were partially converted to aglycones (daidzein and genistein). Soybean proteins were extensively hydrolyzed into oligopeptides and free amino acids, and the soluble peptide fraction (451-189 Da) increased from 4.6% to 86%. Whole-genome sequencing of S. harbinensis M1 revealed a 3,592,195 bp circular chromosome with 53.02% (G + C) content and 3375 coding genes. Metabolic prediction revealed the enzymes required for carbohydrate/pyruvate metabolism and isoflavone biotransformation. The whole proteolytic system was predicted, including peptide transport system and 66 genes encoding proteinases/peptidases. S. harbinensis M1 significantly (p < 0.05) improved the antioxidant activity and antiproliferative effects of soymilk against HepG2/MCF-7 cells. These findings suggest that S. harbinensis M1 can be used as a proteolytic starter-culture to make functional fermented foods.