ISOFLAVONES AND THEIR CONJUGATES IN SOY FOODS - EXTRACTION CONDITIONSAND ANALYSIS BY HPLC MASS-SPECTROMETRY

Identification of isoflavone glycosidic conjugates from several soy pr oducts was carried out by HPLC-mass spectrometry. Positive ion mass sp ectra obtained using the heated nebulizer-atmospheric pressure chemica l ionization interface gave the most sensitive and structurally useful information about each isoflavone conjugate. Although extraction of i soflavones from soy products with 80% aqueous methanol at room tempera ture was just as efficient as at 60-80 degrees C, extraction at higher temperatures caused changes in isoflavone composition and should be a voided. Soybeans and defatted soy flour (which had been minimally heat ed during their preparation) contained mostly isoflavone 6''-O-malonyl glucoside conjugates, with lesser quantities of the beta-glucosides an d only trace amounts of 6''-O-acetylglucoside conjugates. Soy milk, to fu, and soy molasses, each of which involves heating to 100 degrees C during their manufacture, contained mostly isoflavone beta-glucosides. Toasted soy flour and an isolated soy protein had moderate amounts of each of the isoflavone conjugates.