An Optimized Method for the Quantification of Isoflavones in Dry Soy Extract Containing Products

Abstract

Isoflavones, a class of flavonoids with estrogen-like activity, are present in the human diet mainly derived from soy-based foods. Soy isoflavones (namely genistein, daidzein, and glycitein and their derivatives) and concentrates have primarily been investigated for their ability to prevent sex hormone-dependent cancers and cardiovascular problems. Several studies demonstrated that many of the biological effects of soy are due to isoflavones. The aim of our study was to develop a simple method for the determination of isoflavones in dry soy extract containing products. Since biological effects of soy isoflavones depend upon aglycone forms, extracts were hydrolyzed to gain isoflavone aglycones. To optimize the extraction and hydrolysis of isoflavones, the effect of HCl concentration (1.5–6 N), hydrolysis time (25–210 min), and temperature (30–100 °C) on total isoflavone aglycone content was studied using an RP-HPLC-DAD method. By mathematical fitting and optimization methods, optimum hydrolysis conditions for maximizing the quantification of isoflavones were determined (t = 96 min, cHCl = 4.9 N, T = 80 °C). The experimentally verified model has a good coefficient of R 2 (0.9928), and the recovery of isoflavones was 97.81–102.76 %. The developed method allows reliable and maximum determination of isoflavones in dry soy extract containing products. Based on this method, six soy extract containing products were analyzed. Our experiments revealed significant variations in the isoflavone content and composition. These results highlight the necessity to clearly specify the isoflavone composition of soy products.