Systematic evaluation of pre-HPLC sample processing methods on total and individual isoflavones in soybeans and soy products

摘要

There are mainly two protocols in isoflavone analysis, one that involves hydrolysis prior to HPLC analysis and the other direct HPLC analysis. In this study, three different hydrolysis methods were systematically re-evaluated, and compared with direct HPLC analysis. Acidic hydrolysis (1.2-3 M HC1 in ethanol at 80 ℃) showed a maximum conversion of ca. 92% from glucosides to aglycones in 2 h; however, longer reaction caused degradation of genistein. Alkaline hydrolysis using 2 M NaOH converted acetylglucosides and malonylglucosides to their respective glucosides within lOmin. Clucuronidase from H. pomatia effectively converted isoflavone glucosides and acetylglucosides to aglycones. Quantification of the total isoflavones in various soy food products showed no significant difference among direct injection and the three hydrolysis methods (P<0.05). We conclude that direct analysis of isoflavones in crude extracts is a rapid and accurate method to obtain isoflavone profiles and compositions in soybean, soy foods and beverages.