Improved sample treatment and chromatographic method for the determination of isoflavones in supplemented foods

Isoflavones are a group of substances that belong to the family of phytoestrogens. These natural substances may offer several benefits to human health. One of the most important sources for human isoflavone intake is soy and soybean food derivatives. An improved sample treatment followed by a high performance liquid chromatographic method for the determination of isoflavones in supplemented milk and juices is proposed and compared to the AOAC official method. Detection limits found were between 0.2 and 0.3 mg L−1 for daidzein and genistein respectively. Quantification limits found were between 0.7 mg L−1 for daidzein to 1.0 mg L−1 for genistin, while inter and intra-day variability was under 10% in all cases. Recoveries for spiked samples were over 90% and under 110%. The method was validated by comparison with the AOAC method and by recovery assay methodology.