Five strains of bifidobacteria were screened for b-glucosidase activity using p-nitrophenyl-b-Dglucopyranoside as the substrate, and selected strains were used to ferment soymilk. Enumeration of viable bifidobacteria and quantification of isoflavones using HPLC were performed at 0, 12, 24, 36, and 48 h of incubation. Four strains produced b-glucosidase. B. pseudolongum and B. longum-a displayed the best growth in soymilk, with an increase of 1.3 log 10 CFU/mL after 12 h. B. animalis, B. longum-a, and B. pseudolongum caused hydrolysis of isoflavone malonyl-, acetyl-and b-glucosides to form aglycones, and transformed daidzein to equol in soymilk. Fermentation of soymilk with Bifidobacterium sp. resulted in a significant increase (p < 0.05) in the concentration of aglycones.

Soymilk prepared using soy-protein isolate supplemented with D-glucose and L-cysteine was fermented with 4 strains of Bifidobacterium. Enumeration of bifidobacteria and quantification of isoflavones using HPLC were performed at 0, 12, 24, 36, and 48 h of incubation. Supplementation did not significantly enhance (p > 0.05) the growth of bifidobacteria between 0 and 12 h, but did after 12 h. The increase in concentration of isoflavone aglycones and equol was significantly lower (p < 0.05) in supplemented soymilk after 24 h when compared to plain soymilk. Supplementation increased the concentration of aglycones by 0.796 mg/100 mL in soymilk fermented with B. animalis between 12 and 24 h, and the population by 1.27 log 10 CFU/mL (p < 0.05).

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Four strains of Bifidobacterium were assessed for a-galactosidase activity in MRS broth using p-nitrophenyl-a-d-galactopyranoside as substrate. Bifidobacteria were then used to ferment soymilk prepared from soy protein isolate (SPI), with and without d-glucose and l-cysteine supplementation. Measurements of pH and the quantification of oligosaccharides, organic acids and aldehydes in soymilk were done after 0, 12, 24, 36 and 48 h of incubation. The presence of d-raffinose stimulated the a-galactosidase activity of B. longum BB536 (BB536) and B. pseudolongum 20099 (BP20099). In soymilk, oligosaccharides and aldehydes were effectively metabolized by Bifidobacterium; d-glucose and l-cysteine supplementation enhanced the hydrolysis of raffinose and stachyose. BB536 and BP20099 degraded a significantly greater level of oligosaccharides and aldehydes than B. animalis Bb-12 and B. longum 1941 (P < 0.05). Raffinose and stachyose were completely metabolized by BB536 after 48 h. In soymilk without any supplementation, hexanal and pentanal were not detected after 12 h of fermentation with BB536 and BP20099. BB536 was the highest producer of organic acids, with an average acetic acid/l(+)-lactic acid ratio of 0.7.

We investigated the effects of consuming an isoflavone aglycone-enriched soya milk containing viable bifidobacteria on urinary isoflavone excretion and percentage recovery. Sixteen postmenopausal women were randomly divided into two groups to consume either fermented or non-fermented soya milk. Each group participated in a double-blind, crossover study with three 14 d supplementation periods, separated by a 14 d washout. Subjects ingested three daily dosages of isoflavone via the soya milk and collected four 24 h pooled urine specimens per supplementation period. Soya milks were prepared with soya protein isolate and soya germ, followed by fermentation with bifidobacteria. Isoflavone levels were quantified using HPLC. Non-fermented soya milks at 20, 40 and 80 mg isoflavone/200 ml contained 10 %, 9 % and 7 % aglycone, respectively, with their fermented counterparts containing 69 %, 57 % and 36 % aglycone (P,0·001). A trend to a greater percentage urinary recovery of daidzein and glycitein was observed among women consuming fermented soya milk at a dosage of 40 mg isoflavone (P¼ 0·13). A distinct linear dose response for the fermented soya milk group (R 2 ¼ 0·9993) compared with the non-fermented group (R 2 ¼ 0·8865) suggested less interindividual variation in isoflavone absorption. However, total urinary isoflavone excretion was similar for both groups (P.0·05), with urinary isoflavone recovery at approximately 31 %. Increasing the isoflavone dosage correlated positively with its urinary excretion, but urinary percentage recovery of isoflavone was inversely related to dosage level. Hence, a modest dosage ranging from 20 to 30 mg/d may provide the most bioavailable source of isoflavone, regardless of whether it is via an aglycone-rich fermented soya milk or a glucoside-rich soya milk.Isoflavone: Bifidobacteria: Soya milk: Bioavailability: Postmenopausal women Diminishing levels of oestrogen caused by ovarian failure, inadequate to maintain oestrogen-dependent tissues, are associated with higher rates of chronic disease in postmenopausal women. Phytoestrogens, a group of non-steroidal plant-derived compounds, are structurally similar to oestrogen and thus able to exert weak oestrogenic effects (Mayr et al. 1992;Markiewicz et al. 1993). Specifically, isoflavone phytoestrogens found abundantly in soyabeans are bioactive di-phenolic structures able to bind to oestrogen receptor sites (Setchell & Cassidy, 1999). Isoflavones behave in a similar manner to selective oestrogen-receptor modulators, acting as oestrogen agonists and antagonists in different tissues (Brzezinski & Debi, 1999). Hence, isoflavones have been associated with the prevention of hormone-dependent disorders based on epidemiological (Lee et al. 1991;Setchell, 1995;Cassidy, 1996) and small-scale human clinical studies (Anderson et al. 1995;Kurzer, 2000). Soyabeans contain three types of isoflavone, each type being present in four chemical forms. Aglycone structures of daidzein, genistein and glycitein are those forms with an oestrogen-like configuration ...