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SECOND INTERNATIONAL SYMPOSIUM
ON THE ROLE OF SOY
IN PREVENTING AND TREATING CHRONIC DISEASESeptember 15-18, 1996
Brussells, Belgium
SCIENTIFIC PROGRAM
Satellite Symposium
Soybean Isoflavones :
Levels in Foods and PharmacokineticsSoy Isoflavones in Foods: Quality Assurance in Analysis
Patricia A. Murphy, Kobita Barua, Tongtong Song, Gwendolyn Buseman, Huei-ju Wang, Department of Food Science & Human Nutrition, Iowa State University, Ames, IA 50011 USA.
Development of a database for soy isoflavone in foods requires accurate and precise evaluation of different food matrices. To evaluate accuracy, we estimate recoveries of both internal and external standards in 5 different soyfoods weekly. Standards are evaluated daily for system quality assurance. To evaluate sample precision, we analyze soybeans and soymilk for within-day precision and over 4 days for day-to-day precision bimonthly. Coefficients of variation should be 8%. We have validated our methods for single and multiple recovery levels using our internal standard, 4-hydroxybenzyl 1-2,4,6-trhydroxyphenyl ketone, and external standards, daidzein, genistein and genistin. Levels of 12 isoflavones (genistein, daidzein and glycitein; their glucosides, their malonylglucosides, and their acetylglucosides) have been measured in a variety of soybeans and soyfoods. Extraction methods vary depending on soyfood type. The isoflavone levels and forms in soymilk, tofu, tempeh, protein isolate, miso and soy sprouts have been evaluated during soyfood processing. Since the 4 forms change with heat and/or hydration, the isoflavone distribution can be used to document the processing history. The glucoside forms are almost 2X the molecular weight of the aglycones, the reported isoflavone levels should be normalized to the aglycone mass (or an isoflavonoid equivalent) rather than a simple sum of all isomers.Soy Symposium Home http://soyfoods.com/symposium/
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