THE MEASUREMENT OF THE ISOFLAVONE DAIDZEIN BY TIME-RESOLVED FLUORESCENT IMMUNOASSAY - A METHOD FOR ASSESSMENT OF DIETARY SOYA EXPOSURE

We report a novel method for the measurement of urinary daidzein that is suitable for assessment of dietary soya exposure. The method incorp orates the following features: (i) a highly specific monoclonal antibo dy to daidzein (clone 4E4) raised through the 7 position of daidzein a nd (ii) a europium labeled ovalbumin daidzein conjugate. In the presen t format, dilute urine samples of subjects who ingested soy milk are h ydrolyzed with beta-glucuronidase for 30 min on rabbit anti-mouse coat ed plates. Afterwards, the specific monoclonal antibody to daidzein, c lone 4E4, and europium labeled ovalbumin daidzein conjugate are added. After 1 h incubation, the wall bound fluorescence of europium is meas ured by time resolved fluorescence and is inversely proportional to th e concentration of daidzein over the range 0.1-10 ng daidzein/well. Th e method demonstrates good sensitivity, precision and comparability wi th the chemical method GC-FID. Unlike the chemical method, the present immunoassay technique for daidzein is applicable for the measurement of large amounts of samples in epidemiological studies for the assessm ent and monitoring of human exposure to soya food. (C) 1998 Elsevier S cience Ltd. All rights reserved.