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 their phytoestrogen content (measured as genistein equivalents). The validation of the assay for use with food extracts has been demonstrated by investigation of recoveries after acidic and enzymic hydrolysis, by investigation of matrix effects, and by comparison of results with HPLC analysis. Phytoestrogen levels in soy products analyzed ranged between 520 and 1872 μg of genistein equiv/g of soy flour, 5−282 μg/g of soy concentrates, 503−1292 μg/g of soy-protein isolates, and 108−226 μg/g of soy-based infant formulas. Samples of textured vegetable protein and bread containing soy and linseed gave values of 1114 and 68 μg/g, respectively. Comparison of results for 12 samples analyzed both by the receptor assay and by HPLC showed good correlation (r 2 = 0.905). The assay, which is rapid and simple to perform, is suitable for screening phytoestrogen-containing foods in order to assess human exposure to these bioactive compounds. The assay sensitivity is 3.4 μg/g, and 14 samples/plate can be analyzed in 4 h following hydrolysis. Keywords: Phytoestrogens; estrogenic isoflavonoids; receptor assay; screening; soy-based food