Optimization of lactic acid fermentation conditions for fermented tofu whey beverage with high-isoflavone aglycones

Four lactic acid bacteria strains (Lactobacillus paracasei, Leuconostoc mesenteroides, Lactobacillus rhamnosus GG and Lactobacillus plantarum), possessing β-glucosidase enzyme activity, were investigated for tofu whey fermentation based on the capacity of bioconversion of isoflavones. The results suggested that the mixture of L. rhamnosus GG and L. paracasei had great potential for efficient enrichment of bioactive isoflavone aglycones and the percentage composition (daidzein, genistein) increased from 4.6 to 93.78% after fermentation of tofu whey. At the same time, the viable cell counts of the mixture of L. rhamnosus GG and L. paracasei increased to 9.13 log10 CFU/mL while pH value dropped to 4.48 and titratable acidity was 0.28%. Headspace solid-phase microextraction method followed by gas chromatography-mass spectrometry analysis indicated that the odor compounds, particularly the aldehydes and alcohols, were metabolized to trace or undetected levels after fermentation. This research provided not only a new way to develop a functional probiotic beverage enriched in isoflavone aglycones, but also provided a potentially valuable new use for soy whey protein.