Scientific Program (Oral Abstracts) | Poster Abstracts | Speaker List
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 PharmacokineticsChemical Modification of Isoflavones in Soy Foods During Cooking and Processing
L. Coward, M. Smith, M. Kirk and S. Barnes
Department of Pharmacology & Toxicology, and Comprehensive Cancer Center Mass Spectrometry Shared Facility, University of Alabama at Birmingham, AL 35294, USA.
Although for many years it was assumed that soybeans contained large amounts of isoflavones as their -glucosides ( Glc), the principal chemical forms of isoflavones in the soybean are their 6"-O-malonyl- -glucoside (6OMalGlc) conjugates. Because of the inherent chemical instability of this conjugate, experiments were carried out to determine (1) the best conditions for extraction of isoflavones from soy food products and (2) the effects of commercial processing procedures and of cooking on isoflavone concentrations and composition. Hot alcohol extraction of ground soybeans caused de-esterification of the 6OMalGlc conjugates. Room temperature extraction slowed the conversion, but if left at room temperature overnight substantial de-esterification occurred. Extraction at 4oC for 2-4 hours caused the highest yield of 6OMalGlc conjugates and the lowest proportion of Glc conjugates. The amounts of the 6"-O-acetyl- -glucoside (6OAcGlc) conjugates did not change in these experiments. Commercial soy food products were analyzed by reversed-phase HPLC-mass spectrometry for their isoflavone content. These studies revealed that defatted soy flour which had not been heat-treated consisted mostly of 6OMalGlc conjugates; in contrast, toasted soy flour contained large amounts of 6OAcGlc conjugates, presumably formed by heat-induced decarboxylation of the malonate group to acetate. Soy milk and tofu, formed by hot aqueous extraction of soybeans, consisted almost entirely of Glc conjugates; low-fat versions of these products were substantially depleted of isoflavones. Alcohol-washed soy protein concentrates also contained very little isoflavones. Isolated soy protein and textured vegetable protein consisted of a mixture of all three types of isoflavone conjugates. Baking or frying of textured vegetable protein at 375oF did not alter the total isoflavone content, but there was a steady increase in Glc conjugates at the expense of 6OMalGlc conjugates. Similar, but more marked, effects were observed in the cooking of soy flour in soy cookies. Under the most extreme cooking conditions (leading to hardly edible foods), unconjugated isoflavones became the predominant form, and the total amount of extractable isoflavones decreased.Supported by grants from the NCI (CA-61668 & CA-13148), the United Soybean Board and Protein Technologies International.
Soy Symposium Home http://soyfoods.com/symposium/
U.S. Soyfoods Directory Home http:soyfoods.com/
© Copyright 1997
Indiana Soybean Board