Changes in equol and major soybean isoflavone contents during processing and storage of yogurts made from control or isoflavone-enriched bovine milk determined using LC-MS (TOF) analysis

- Occurrence of soybean isoflavones in fresh and mature yogurts was studied.
- Yogurts were made from conventional and isoflavone-enriched milk.
- Fermentation caused changes in daidzein and glycitein content.
- Maturation of yogurts had only minor effect on isoflavones content.
- LC-MS (TOF) method was employed to determine the isoflavone content in yogurts.

The effect of supplementing a basal diet for dairy cows with “Soybean extract 40” (Biomedica, Prague, Czech Republic), containing 40% soybean isoflavones, on the contents of daidzein, glycitein, genistein, and equol in milk as well as fresh and mature yogurts was estimated. To determine the contents of these isoflavonoids, an efficient analytical LC-MS (TOF) technique was used. The “Soybean extract 40” used in our study contained an especially high proportion of daidzein (307 g kg−1). In both milk and yogurt samples, the amounts of daidzein and its metabolite equol were significantly higher in samples obtained from cows that received the isoflavone extract-supplemented diet than from those that received the basal diet, as the precursor daidzein contributed to the increased equol concentrations. Fermentation caused significant changes in the daidzein and glycitein concentrations. With maturation, the concentrations of daidzein and equol were unaffected, while the glycitein concentration decreased significantly.