Abstract: Three batches of yogurts were made with soy protein
isolate (SPI) supplemented with 2% (S2), 4% (S4) or 6% (S6) of
skim milk powder (SMP). The fourth batch (control; S0) was
prepared from SPI without SMP supplementation. Lactobacillus
delbrueckii ssp. bulgaricus ATCC 11842 (Lb 11842) and
Streptococcus thermophilus ST 1342 (ST 1342) were used as the
starter culture. Biotransformation of the inactive forms, isoflavone
glycosides (IG) to biologically active forms, isoflavone aglycones
(IA), was determined during 28 d storage. The viability of both
microorganisms was significantly higher (P < 0.05) in S2, S4, and S6
than that in S0. The ratio of lactic acid/acetic acid in S0 was in the
range of 15.53 – 22.31 compared to 7.24 – 12.81 in S2, S4 and S6.
The biotransformation of IG to IA in S2, S4 and S6 was also
enhanced by 9.9 -13.3% compared to S0.