Isoflavone phytoestrogen
degradation in fermented soymilk with selected β-glucosidase producing L. acidophilus strains during storage at different temperatures
D.O. Otienoa, 
, J.F. Ashtonb and N.P. Shaha, 
aSchool of Molecular Sciences, Victoria University, Werribee Campus, P.O. Box 14428, Melbourne, Victoria 8001, Australia
bSanitarium Health Food Co. Freemans Drive, Cooranbong, New South Wales, Australia
Received 31 May 2006; revised 9 August 2006; accepted 8 October 2006. Available online 15 December 2006.
Abstract
Soymilk fermented with 3 selected Lactobacillus acidophilus strains were stored at various temperatures (− 80 °C, 4 °C, 25 °C and 37 °C) for 8 weeks and the concentration of isoflavones determined weekly using RP-HPLC. The decreasing concentration of isoflavones in soymilk during storage due to degradation was found to fit the first order kinetics model. Isoflavone aglycones as well as isoflavone glucosides largely appeared to be stable during storage (P < 0.01). Interestingly, the aglycone forms showed much smaller degradation as compared to glucoside forms at all the storage temperatures studied. Of the isoflavone aglycones, daidzein was found to be the most stable followed by genistein, while glycitein was least stable. Isoflavone aglycones such as glycitein, daidzein and genistein showed smaller degradation constants in fermented soymilk at lower storage temperatures (− 80 °C and 4 °C) and higher degradation constants at higher storage temperatures (25 °C and 37 °C) with each strain. In contrast, glucosides glycitin and daidzin showed higher degradation at lower storage temperatures (− 80 °C and 4 °C) and lower degradation at higher storage temperatures (25 °C and 37 °C). Storage temperature was therefore found to be very important in regulating the rate of degradation soy isoflavones in fermented soymilk.
Keywords: Isoflavones; Bioactive; Stability; Degradation kinetics; Biotransformation; Lactobacillus acidophilus
