| Summary: | 碩士 === 輔仁大學 === 食品營養學系 === 90 === Isoflavones belong to a class of flavonoids, and is mainly present in soybean. Twelve isomers of isoflavones have been identified in soybean products. The current method used for analysis of isoflavones has some drawbacks, for instance, low recovery and long separation time. Thus it is necessary to develop a better method. Soy milk is a soybean product rich in nutrients. However, during processing of soy milk the conversion between isoflavone isomers may decrease its biological activity. The objectives of this study was to develop an appropriate method for extraction and separation of isoflavones and investigate the effect of temperature on the isoflavone stability in soy milk.
Results showed that the best HPLC condition could be achieved by using a Vydac 201TP54 C18 column, and a mobile phase of acetonitrile(A) and water(B) with the following gradient elution: 5% A in B initially, increased to 10% A in 5 min, 25% A in 15 min, 32% A in 22 min and returned to 5% A in 27 min. The flow rate was 2 mL/min amd detection wavelength was 262 nm. Twelve isoflavones were resolved within 20 min, which is faster than the other methods reported in the literature. Also, with acetone and 20% 0.1N HCl (volume ratio) as solvent, the best extraction efficiency could be obtained. Shaking for 2 hours was found to possess a better extraction effect than sonication for 1 hour. In addition, by employing a defatting step the contents of isoflavones could be substantially increased. The levels of isoflavones and aglycons decreased with increasing temperature during processing of soy milk, and in the meantime, the malonylglucoside isoflavone could be converted to glucoside isoflavone.
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