18B-30 |
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K. MATHIAS, B. Ismail, C. M. Corvalan, and K. D. Hayes. Dept. of Food Science, Purdue Univ., 745 Agriculture Mall Dr., West Lafayette, IN 47907-2009 Increasing evidence has shown that isoflavones from soybeans are associated with lowering the risk of various chronic diseases. The chemical structure of isoflavones affects their absorption and therefore their bioavailability. For isoflavones to be absorbed by the enterocytes of adults, the sugar moiety bound to the flavonoid must be hydrolyzed by b-glycosidases. A recent study has shown that b-glycosidases are hindered when malonyl- and acetyl- groups are esterified at the 6²-O- of the sugar moiety. Previous research has shown that the malonyl- and acetyl- groups are readily removed by heat, yet many soy products on the market still contain large amounts of conjugated isoflavones. Thus, different processing conditions may be used to obtain products with biologically enhanced isoflavone profiles. Our objective was to observe changes in the isoflavone profile after both malonylgenistin and acetylgenistin were subjected to different pH and temperature treatments. Malonylgenistin and acetylgenistin from standards were placed into aqueous solutions of pH 2, 7, and 10, and were incubated at 25 °C, 80 °C, and 100 °C for two h. Samples then were made to 80% methanol solutions and isoflavone profiles were analyzed using reverse phase high performance liquid chromatography. Significant effects of pH, temperature, and their interaction were observed on conversion data (p≤0.05). Results showed that as temperature and pH increased the conversion of malonylgenistin to the b-glycoside form increased. Maximum conversion of acetylgenistin was observed at 80 °C and 100 °C when the pH was 10. Degradation of conjugated isoflavones was found to be the highest at conditions that elicited maximum conversion, with acetylgenistin having lower degradation than malonylgenistin. Our observations indicate that the conversion of conjugated isoflavones to their respective non-conjugated forms can be driven by alkaline conditions and elevated temperatures, thus enhancing the bioavailability of isoflavones in soy products.
Session 18B, Food Chemistry: Antioxidant and bioactive agents
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |