This study evaluated the hydrolysis of isoflavones in soymilk fermented at 37C for 48 h by four different Lactobacillus and Bifidobacterium cocultures. The hydrolysis of isoflavone β‐glucosides significantly increased (P < 0.05) the bioactive aglycones from 36 to over 90% of total isoflavones in soymilk fermented with any of the four Lactobacillus and Bifidobacterium cocultures as compared with unfermented soymilk. Compared with three other cocultures of Lactobacillus and Bifidobacterium, fermentation of soymilk with the Lactobacillus paracasei/Bifidobacterium longum cocultures yielded better isoflavone hydrolytic potential (Otieno‐Shah index) and the highest β‐glucosidase activity after 12 h of incubation. PRACTICAL APPLICATIONS Isoflavones are known as phytoestrogens because they are present in soy products and have estrogen‐like activity. During fermentation, the majority of glucoside isoflavones in soymilk are converted to bioactive aglycones via microorganism‐derived β‐glucosidase. In human intestines, aglycone isoflavones are absorbed faster and in greater amounts than their glucosides. Using probiotic Lactobacillus and Bifidobacterium cocultures to ferment soymilk efficiently increases the bioactive aglycone concentrations. Hence, fermenting soymilk with this coculture could enhance the nutritional value of the product.

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Purpose -The purpose of this paper is to investigate isoflavone aglycone concentrations in commercial soybean and soybean products in Taiwan. Design/methodology/approach -Isoflavone concentration was determined by high performance liquid chromatography method. The samples included soybeans, non-fermented (tofu, soymilk, soybean meal) and fermented (natto, miso and sufu) soybean products. Findings -The total isoflavone concentration in soybean and soybean products was approximately 109-508 mg/100 g. Isoflavone aglycones had the concentration of 2-19 per cent of total isoflavones in soybeans and non-fermented soybean products. There was a broad diversity of isoflavone aglycones at 4-94 per cent of total isoflavones in fermented soybeans. Originality/value -The study provides new information about distribution of bioactive isoflavone aglycones in soybean and soybean products. Isoflavone glucosides were the major components in all soybean and non-fermented products, while isoflavone aglycones were abundant in sufu and partially in miso of soybean fermented products. The information should be used to establish that positive consumption of bioactive aglycones isoflavones may be more efficient for improving the physiological functions for human health.