Evaluation of enzymic potential for biotransformation of isoflavone phytoestrogen in soymilk by Bifidobacterium animalis, Lactobacillus acidophilus and Lactobacillus casei Daniel O. Otieno a , John F. Ashton b , Nagendra P. Shah a, * a School of Molecular Sciences, Victoria University, Werribee Campus P.O. Box 14428, Melbourne City Mail Centre, Vic. 8001, Australia b Sanitarium Health Food Co., Freemans Drive, Cooranbong, NSW, Australia Received 2 February 2005; accepted 22 August 2005 Abstract Three strains of Lactobacillus acidophilus, two of Lactobacillus casei and one of Bifidobacterium were screened for b-glucosidase activ- ity using q-nitrophenyl-b-D-glucopyranoside as a substrate and their potential for the breakdown of isoflavone glucosides to the biolog- ically active aglycones in soymilk. Isoflavones quantification with HPLC and b-glucosidase activity were performed after 0, 12, 24, 36, and 48 h of incubation in soymilk at 37 °C. All six micro-organisms produced b-glucosidase, which hydrolysed the predominant isoflav- one b-glucosides. There was a significant increase and decrease (P < 0.05) in the concentration of isoflavone aglycones and glucosides, respectively, in fermented soymilk. Based on the concentration of isoflavones during peak b-glucosidase activity, the hydrolytic potential was calculated. L. acidophilus 4461 had the highest aglycone concentration of 76.9% after 24 h of incubation, up from 8% in unfermented soymilk (at 0 h). It also had the best isoflavone hydrolytic index of 2.01, signifying its importance in altering the biological activity of soymilk. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Bifidobacterium; Lactobacillus; b-Glucosidase activity; Isoflavones; Aglycone 1. Introduction For many centuries, soy has been a common part of the diet in many countries. As a result, isoflavones, naturally occurring phytoestrogens components of soy has been con- sumed in substantial quantities by those populations whose soy intake is high. Asian populations, with their high in- take (50–70 mg/d) of soy-derived isoflavones, are known to have a low incidence of osteoporosis, menopausal symp- toms and mortality from cardiovascular disease (Nagata, Takatsuka, Kurisu, & Shimizu, 1998). On the other hand, isoflavone intake is generally less than 2 mg/d in Western countries (De Kleijn, van der Schouw, & Wilson, 2001; Jones, Price, & Fenwick, 1989). There have been many reports in the recent literature describing soybean isoflavones from epidemiological-, bio- chemical-, mechanistic-, pharmacological-, and toxicologi- cal perspectives. There have been, however, no reports of adverse effects from consumption of soymilk (Munro et al., 2003). Studies investigating the metabolic properties of isoflavones have indicated that they are readily ab- sorbed, metabolised, and excreted, although individual and sex-related differences have been reported (Munro et al., 2003). The phytoestrogens found abundantly in soy- beans consist of the diphenolic, isomeric family of com- pounds known as isoflavones. There are three structural ‘‘families’’ of the isoflavones found in soy foods, namely, the aglycones, glucosides, malonyl-, and acetyl-glucosides (King & Bignell, 2000). 0963-9969/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2005.08.010 * Corresponding author. Tel.: +61 3 9919 8289; fax: +61 3 9919 8284. E-mail addresses: Nagendra.Shah@vu.edu.au, shah@vu.edu.au (N.P. Shah). www.elsevier.com/locate/foodres Food Research International 39 (2006) 394–407