Content composition and antioxidant activity of isoflavones in commercial and homemade soymilk and tofu

School of Kinesiology and Nutritional Science, California State University, Los Angeles, CA 90032, USA
Journal of the Science of Food and Agriculture (Impact Factor: 1.71). 12/2007; 87(15):2844 - 2852. DOI: 10.1002/jsfa.3041


BACKGROUND: Isoflavones, found in soymilk and tofu, are one of the phytochemicals in soy-based products that may promote good health. Homemade tofu and various homemade soymilk samples were made using different soaking, grinding, and cooking methods. The homemade samples were compared to commercial tofu and soymilk for total isoflavone content and composition as well as their antioxidant capacity. All samples were freeze-dried and extracted with a 58% acetonitrile solution which was subsequently used to determine the isoflavone content by reverse-phase high-performance liquid chromatography. The antioxidant activity of extracts was determined using a modified 2,2-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) method and total antioxidant capacity was reported as ascorbic acid equivalents.RESULTS: The total isoflavone, aglycone, and antioxidant levels were significantly higher in homemade soymilk and tofu (1571 µg) than in commercial samples. Homemade soymilk made by the extended boiling method yielded the highest total isoflavone (2567 µg) and glucoside (1525 µg) content. A strong positive correlation was observed between the total isoflavone, aglycone conjugates, and genistein series concentration and antioxidant capacity of soymilk.CONCLUSION: Increased moist heating time yielded the highest concentration of total isoflavones as well as aglycone conjugates and the genistein series. Increasing the duration of boiling can increase the isoflavone content of both homemade and commercial soymilk and tofu. Copyright © 2007 Society of Chemical Industry

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    • "Wang and Murphy (1996) reported an increase in the isoflavone recovery by pressing the okara. Regarding the profile, the soymilk contains a lower percentage of aglycones and 6″-O-acetyl-genistin than the okara, but due to the low solubility of aglycones in the aqueous media, the soymilk contains a higher concentration of glucosides and malonyl conjugates (Ishihara et al. 2007; Jackson et al. 2002). "
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