Systematic evaluation of pre-HPLC sample processing methods on total and individual isoflavones in soybeans and soy products |
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Authors: | Suqin Shao Alison M. DuncanRaymond Yang Massimo F. MarconeIstvan Rajcan Rong Tsao |
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Affiliation: | a Guelph Food Research Centre, Agriculture & Agri-Food Canada, 93 Stone Road West, Guelph, Ontario, Canada N1G 5C9b Department of Human Health and Nutritional Sciences, University of Guelph, 50 Stone Road East, Guelph, Ontario, Canada N1G 2W1c Department of Food Science, University of Guelph, 50 Stone Road East, Guelph, Ontario, Canada N1G 2W1d Department of Plant Agriculture, University of Guelph, 50 Stone Road East, Guelph, Ontario, Canada N1G 2W1 |
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Abstract: | 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 HCl in ethanol at 80 °C) 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 10 min. Glucuronidase 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. |
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Keywords: | Soybean Isoflavone Glucosides Acetylglucosides HPLC Hydrolysis Direct analysis |
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