American Journal of Clinical Nutrition, Vol 68, 1474S-1479S, Copyright © 1998 by The American Society for Clinical Nutrition, Inc

ORIGINAL RESEARCH COMMUNICATIONS

Soy isoflavone analysis: quality control and a new internal standard

T Song, K Barua, G Buseman and PA Murphy
Department of Food Science and Human Nutrition, Iowa State University, Ames 50011, USA.

Development of a database of the soy isoflavone content of foods requires accurate and precise evaluation of different food matrixes. To evaluate accuracy, we estimated recoveries of both internal and external standards in 5 different soyfoods weekly. Standards were evaluated daily for system quality assurance. To evaluate sample precision, we analyzed soybeans and soymilk bimonthly for within-day precision and over 4 d for day-to-day precision. CVs should be < or = 8%. We validated our methods for single and multiple recovery concentrations by using our new internal standard, 2,4,4'- trihydroxydeoxybenzoin, and the external standards daidzein, genistein, and genistin. Concentrations of 12 isoflavone isomers, 3 aglycones (daidzein, genistein, and glycitein), and 9 glucosides (daidzin, genistin, glycitin, acetyldaidzin, acetylgenistin, acetylglycitin, malonyldaidzin, malonylgenistin, and malonylglycitin) were measured in a variety of soybeans and soyfoods. The extraction methods used depended on soyfood type. The HPLC conditions for soy isoflavone analysis were improved, leading to good separation with a short analysis time (60 min/sample). A data bank of concentration and distribution of isoflavones in different soybean products was assembled. A wide range of isoflavone concentrations, from < 50 microg/g to > 20,000 microg/g, was found in different soy products. The glucoside forms are almost twice the molecular weight of the aglycones; reported isoflavone concentrations should be normalized to the aglycone mass (or an isoflavonoid equivalent) rather than a simple sum of all isomers.

This article has been cited by other articles:

				M. I. Genovese, N. M.A. Hassimotto, and F. M. Lajolo Isoflavone Profile and Antioxidant Activity of Brazilian Soybean Varieties Food Science and Technology International, June 1, 2005; 11(3): 205 - 211. [Abstract] [PDF]

				Y. Zheng, S.-O. Lee, M. A. Verbruggen, P. A. Murphy, and S. Hendrich The Apparent Absorptions of Isoflavone Glucosides and Aglucons Are Similar in Women and Are Increased by Rapid Gut Transit Time and Low Fecal Isoflavone Degradation J. Nutr., October 1, 2004; 134(10): 2534 - 2539. [Abstract] [Full Text] [PDF]

				T. Song, S.-O. Lee, P. A. Murphy, and S. Hendrich Soy Protein With or Without Isoflavones, Soy Germ and Soy Germ Extract, and Daidzein Lessen Plasma Cholesterol Levels in Golden Syrian Hamsters Experimental Biology and Medicine, October 1, 2003; 228(9): 1063 - 1068. [Abstract] [Full Text] [PDF]

				Y. Zheng, J. Hu, P. A. Murphy, D. L. Alekel, W. D. Franke, and S. Hendrich Rapid Gut Transit Time and Slow Fecal Isoflavone Disappearance Phenotype Are Associated with Greater Genistein Bioavailability in Women J. Nutr., October 1, 2003; 133(10): 3110 - 3116. [Abstract] [Full Text] [PDF]

				E. Gianazza, I. Eberini, A. Arnoldi, R. Wait, and C. R. Sirtori A Proteomic Investigation of Isolated Soy Proteins with Variable Effects in Experimental and Clinical Studies J. Nutr., January 1, 2003; 133(1): 9 - 14. [Abstract] [Full Text] [PDF]

				K. D. R. Setchell Soy Isoflavones--Benefits and Risks from Nature's Selective Estrogen Receptor Modulators (SERMs) J. Am. Coll. Nutr., October 1, 2001; 20(90005): 354S - 362. [Abstract] [Full Text]

				A. Drewnowski and C. Gomez-Carneros Bitter taste, phytonutrients, and the consumer: a review Am. J. Clinical Nutrition, December 1, 2000; 72(6): 1424 - 1435. [Abstract] [Full Text] [PDF]

				Patrick De Boever, B. Deplancke, and W. Verstraete Fermentation by Gut Microbiota Cultured in a Simulator of the Human Intestinal Microbial Ecosystem Is Improved by Supplementing a Soygerm Powder J. Nutr., October 1, 2000; 130(10): 2599 - 2606. [Abstract] [Full Text]