QUANTITATION OF PHYTOESTROGENS IN LEGUMES BY HPLC

A fast, sensitive, and precise method is presented for the efficient extraction and quantitation of coumestrol, daidzein, genistein, formononetin, and biochanin A from foods by diode array reversed-phase HPLC analysis using flavone as internal standard. Acid hydrolysis during extraction of foods was chosen to convert the various phytoestrogen conjugates into their respective aglycons, facilitating HPLC analysis and allowing quantitation of total phytoestrogens as aglycons including originally present glycosides, ''free'' aglycons, and those conjugates which are below the detection limit in food plants. Extraction efficiencies and HPLC conditions were evaluated and optimized, leading to precision and spiking recovery values of 3-8% and 94-104%, respectively, depending on the analyte. Phytoestrogen levels from more than 40 food items, mostly legumes, were determined using this method. High levels of daidzein and genistein were found in soy products and black beans, whereas sprout items were found to be rich in coumestrol and formononetin.