Role of microbial strain and storage temperatures in the degradation of isoflavone phytoestrogens in fermented soymilk with selected β-glucosidase producing Lactobacillus casei strains

Soymilk fermented with 2 Lactobacillus casei strains were stored at various temperatures (80 °C, 4 °C, 24.8 °C and 37 °C) for 8 weeks and isoflavone concentration analysed at weekly intervals using RP-HPLC. The degradation of each isoflavone compound at each storage temperature was found to fit first order kinetic model. Aglycone as well as glucosides generally appeared to be stable during storage (P < 0.01) at the 4 storage temperatures. Aglycone forms had smaller degradation constants compared to glucosides at all storage temperature and in the presence of both microorganisms. Specifically, aglycones showed a unique trend of smaller degradation at lower storage temperatures (−80 °C and 4 °C) than at higher temperatures (24.8 °C and 37 °C). Glucoside genistin was least stable at all storage temperatures compared to other isoflavones in the fermented soymilk with each strain while aglycone daidzein was the most stable. L. casei 2607 in fermented soymilk stored at 4 °C after 8 weeks gave the least degradation for daidzein of a mere 3.78% loss from 9.53 to 9.17 ng/μL. L. casei 2607 showed greater hydrolytic potential than L. casei ASCC 290 as denoted by higher degradation of isoflavone glucosides in fermented soymilk at lower storage temperatures.