Validation of a novel estrogen receptor-based microtitration plate assay for the determination of phytoestrogens in soy-based foods

A novel, nonisotopic microtitration plate assay based on the human estrogen receptor has been used to screen soy-based and soy-containing foods for th eir phytoestrogen content (measured as genistein equivalents). The validati on of the assay for use with food extracts has been demonstrated by investi gation of recoveries after acidic and enzymic hydrolysis, by investigation of matrix effects, and by comparison of results with HPLC analysis. Phytoes trogen levels in soy products analyzed ranged between 520 and 1872 mu g of genistein equiv/g of soy flour, 5-282 mu g/g of soy concentrates, 503-1292 mu g/g of soy-protein isolates, and 108-226 mu g/g of soy-based infant form ulas. Samples of textured vegetable protein and bread containing soy and li nseed gave values of 1114 and 68 mu g/g, respectively. Comparison of result s for 12 samples analyzed both by the receptor assay and by HPLC showed goo d correlation (r(2) = 0.905). The assay, which is rapid and simple to perfo rm, is suitable for screening phytoestrogen-containing foods in order to as sess human exposure to these bioactive compounds. The assay sensitivity is 3.4 mu g/g, and 14 samples/plate can be analyzed in 4 h following hydrolysi s.