Phytoestrogens in bovine plasma and milk - LC-MS/MS analysis

Phytoestrogens belong to a group of polyphenolic plant metabolites which induce biological responses, based on their structural similarity to 17β-estradiol. In order to investigate the relationship between the levels of these biologically active compounds and beneficial health effects, it is neccesary to quantify accurately their levels in foods and biological fluids. In this study, HPLC-MS/MS method for the determination of isoflavones genistein, daidzein, and estrogenic metabolite-equol in bovine plasma and milk was optimised and validated. The method allowed low limits of detection: 5, 2.5 and 0.5 ng/ml for genistein, daidzein and equol, respectively, thus enabling to determine the effect of phytoestrogen-rich diet on the concentration of isoflavones and the metabolite in biological fluids of cows. The feeding experiment, carried out with four dairy cows, showed that a soy-based diet significantly increased both plasma and milk contents of biologically potent equol, therefore, the latter commodity could be an alternative source of this estrogenic metabolite, namely for the consumers who are not capable to convert it from the isoflavone precursors consumed in the diet.