Develop an isoflavone aglycone-enriched soy milk.

The consumption of modern soy milk prepared from soy protein isolate (SPI) has superseded the consumption of traditional whole bean soy milk. However, soy milk made from SPI has a reduced level of isoflavones due to losses that occur during protein isolation.

Isoflavones are functionally similar to estrogens and are associated with the prevention of hormone-dependent disorders. Soy germ (SG) has the highest concentration of isoflavones. Isoflavones exist in soy milk predominantly at levels greater than 90% as biologically inactive glucosides. Fermentation processing with Bifidobacterium is able to increase the concentration of bioactive and bioavailable aglycones.

The objective of Australian scientists was to increase the level of isoflavones in soy milk by supplementing the product with SG and then biotransforming isoflavone glucosides to bioactive aglycones using Bifidobacterium animalis.

Soy milks were prepared by reconstituting SPI to SG at ratios of 9:1, 6:4 and 3:7. These mixtures then were fermented with B. animalis. The enumeration of viable populations, pH measurements and the quantification of isoflavones using liquid chromatography was performed at 0 hour, 12 hours and 24 hours of incubation and at 1 day, 7 days and 14 days of refrigerated storage.

The viable population of B. animalis increased by 1.1 log10 CFU, 1.3 log10 CFU and 0.9 log10 CFU per mL after 24 hours of incubation in the 9:1, 6:4 and 3:7 mixtures, respectively. The population did not decline after 14 days of refrigeration. The greatest reduction in pH occurred in the 6:4 ratio mixture, which declined to pH 4.38 after 24 hours.

The total isoflavone concentration in the 9:1, 6:4 and 3:7 mixtures was 13.7 mg per 100 mL, 36.9 mg per 100 mL and 60.9 mg per 100 mL, respectively. Fermentation of the 9:1 and 6:4 mixes biotransformed isoflavone glucosides to aglycones, and their concentration in the 9:1 mixture increased from 0.1% to 47.3% after 24 hours.

Soy milk comprising a ratio of 9:1, 6:4 and 3:7 of SPI to SG contained a total isoflavone concentration that was three-, seven- and 12-fold greater, respectively, than conventional soy milk. Fermentation enriched the concentration of bioactive aglycones. So, consuming a high level of bioactive aglycones and probiotic bifidobacteria in soy milk may offer a significant health benefit to consumers.

Further information. Dimitri Tsangalis, Food Safety Authenticity and Quality Unit, Victoria University, P.O. Box 14428, Melbourne City Mail Centre, Melbourne, VIC 8001, Australia; phone: [phone]; email: [e-mail].