Stability of Isoflavones

Due to growing evidence suggesting that isoflavones might protect against various cancers and cardiovascular diseases, it was important to investigate the basic properties of isoflavones and to develop feasible methods for the preparation of large amounts of purified isoflavones for use in further studies. The objectives of this study were: (1) to evaluate the thermostability of pure isoflavones; (2) to investigate the effects of heat treatment on isoflavones in soy liquor; and (3) to study the effects of yeast fermentation on isoflavones and carbohydrates. Isoflavone concentrations were analyzed using an HPLC system. Carbohydrate content was measured spectrophotometerically. The study revealed that pure isoflavones were very thermally stable. Pure genistein and daidzein standards were more thermally stable than genistin. The isoflavones in soy liquor were relatively thermally stable. Aglycones were more thermally stable than their conjugates. The malonyl form was the most unstable one among the four forms of isoflavones. Yeast fermentation had significant effects on isoflavone profiles, but had little effect on the total isoflavone concentrations. Carbohydrates were reduced by 52% and 35% during 8 hr of fermentation at room temperature and 50°C, respectively. The experiments suggested that fermentation might be a potential method for concentrating isoflavones in soy liquor