Determination of some phytoestrogens in soybeans and their processed products with HPLC and coulometric electrode array detection

A reliable and sensitive method for quantification of daidzein and genistei n by HPLC with coulometric electrode array detection is presented using bis phenol A as internal standard. Acid hydrolysis during extraction of foods a llows the quantitative determination of total phytoestrogens as aglycones. The substances are separated on a reversed phase column (Hypersil(R) Elite C-18), eluted with methanol/acetonitrile/50 mM sodium acetate pH 4.8 (40/20 /40, v/v/v) and detected in a coulometric electrode array detector using an oxidative detection mode (+390 to +810 mV in increments of 60 mV, vs palla dium reference electrode). Phytoestrogen levels from several food items wer e determined. High levels of daidzein (819 mg/kg) and genistein (960 mg/kg) were found in soy products whereas biochanin A could not be detected in an y of these food samples. The recovery depends on the kind of food and was f ound to be between 72 and 94% for daidzein and genistein.