Enrichment of isoflavone aglycones in soymilk by fermentation with single and mixed cultures of Streptococcus infantarius 12 and Weissella sp. 4

Soymilk was fermented with either Streptococcus infantarius 12 (Si 12), Weissella sp. 4 (Ws 4), or their mixed cultures with different mixing ratios (Si 12:Ws 4 = 1:1, 1:3, 1:5, and 1:10, v/v) for 12 h at 37 °C. All cultures in soymilk readily proliferated and reached about 108–9 CFU/mL. After 12 h, pH and titratable acidity of soymilk ranged 4.19–4.47 and 0.57%–0.64%, respectively. The pH of soymilk fermented with Si 12 was the lowest while that obtained with Ws 4 the highest. A sharp increase in β-glucosidase (β-glu) activity corresponded well with a rapid decrease in isoflavone glucosides and an increase in aglycone contents. The rate of hydrolysis of isoflavone glucosides was the least with Si 12 while the highest with Ws 4, resulting in about 23%–33% and 98%–99% hydrolysis of the glucosides with Si 12 and Ws 4, respectively, after 12 h. Mixed cultures with 1:3, 1:5, and 1:10 ratios seem to be more effective starters for bioactive fermented soymilk with more aglycones and appropriate acidity in a short time than single cultures.