In the present research, effect of sequential addition of Bifidobacterium bifidum, Bacillus subtilis and Rhizopus oligosporus on content and composition of vitamin K2 and isoflavones in fermented soy foods have been investigated. Initially, soybeans were fermented with B. bifidum; then this fermented mass was re-fermented with co-culture of B. subtilis and R. oligosporus. The evolved sequence of microbes inoculation tended towards significantly (p < 0.5) higher enzymes levels (126.16 ± 2.23 IU/mg lipase, 36.52 ± 1.25 IU/mg phytase and 8.52 ± 1.12 IU/mg β-glucosidase); maximum menaquinone-7 production (9.3 ± 1.27 μg/g); and isoflavone content (84.64 ± 1.97 % daidzein, 99.29 ± 0.86 % genistein, 96.42 ± 1.32 % glycitein) after 72 h of solid-state fermentation. The study showed that co-fermentation of soybean with different microbes in a particular sequence can enhance nutritional value batter than the mono-culture fermentation due to the positive correlation between enzymes (lipase, phytase, β-glucosidase) levels, menaquinone-7 and soy isoflavones content.
Keywords: Isoflavones; Lipase; Menaquinone; Phytase; Soybean fermentation; β- glucosidase.