Bioconversion of Daidzin to Daidzein by Lactic Acid Bacteria in Fermented Soymilk

The purpose of this study is to select LAB that produce daidzein during soymilk fermentation from among 32 strains isolated from Japanese traditional fermented sushi and pickles. Fourteen strains showed more than 0.5% titratable acidity at 48 h fermentation in soymilk. These strains were applied to a daidzein production test. Seven strains including 5 Lactobacillus plantarum strains, 1 Lb. sakei subsp. sakei strain, and 1 Lb. coryniformis strain yielded more than 4.0 µg/g daidzein in soymilk after 48 h fermentation. Lb. plantarum JAB2001 showed the highest titratable acidity (0.5%) and the highest daidzein yield (10.10 µg/g) during soymilk fermentation at 40°C for 12 h. Strain JAB2001 could be used as a starter culture of fermented soymilk products.