Development of ELISAs for the measurement of the dietary phytoestrogens daidzein and equol in human plasma

Microtitration plate ELISAs were developed for the isoflavone daidzein, a phytoestrogen found mainly in soya and the mammalian metabolite of daidzein, equol.The detection limits in assay buffer were 21 pg per well for daidzein and 70 pg per well for equol.The assays were both highly specific.Human plasma was extracted with an organic solvent and standard curves for daidzein and equol were obtained in the presence of the extract.Applications of the assays are discussed.