Antioxidant Properties of Soybean Isoflavone Extract and Tofu in Vitro and in Vivo

Jiabin Liu,† Sam K. C. Chang,*‡ and Dennis Wiesenborn§
Department of Medicine, University of Minnesota, Minneapolis, Minnesota 55455, and Department of Cereal and Food Sciences and Department of Agriculture & Biosystems Engineering, North Dakota State University, Fargo, North Dakota 58105
J. Agric. Food Chem., 2005, 53 (6), pp 2333–2340
DOI: 10.1021/jf048552e
Publication Date (Web): February 25, 2005
Copyright © 2005 American Chemical Society
†

 Department of Medicine, University of Minnesota.

,
*

 Corresponding author. Phone:  (701)231-7485. E-mail:  Kow.Chang@ ndsu.edu.

,
‡

 Department of Cereal and Food Sciences, North Dakota State University.

,
§

 Department of Agriculture & Biosystems Engineering, North Dakota State University.

Abstract

Isoflavones in soybean were extracted in the crude form using 80% food-grade ethanol at 80 °C for 6 h and followed by concentration and dehydration. The soy extract contained isoflavones primarily in the forms of glucosides. In vitro antioxidant activities of the soy extract containing 20−500 ppm isoflavones were conducted using a Rancimat method. The results showed that soy isoflavone extract had strong in vitro antioxidant activity. There was a dose-dependent response for the in vitro antioxidant activity at the lower concentrations but not at the higher concentrations. In vivo antioxidant property was determined by measuring the antioxidant enzymes, superoxide dismutase, and catalase in various organs of rats that were fed with diets containing partially oxidized oil and various levels of isoflavones for up to 24 weeks. Neither short-term (8 weeks) feeding nor low isoflavone content (50 ppm) induced changes in superoxide dismutase or catalase activities in rats. Only diets containing high isoflavone contents (150 and 250 ppm) showed obvious elevated enzymatic levels in various organs. In addition, a laboratory-prepared tofu containing approximately 50 ppm isoflavones had better effects than the soy extract with the 250 ppm isoflavone group, which indicated that molecules other than isoflavones may have a synergistic effect on in vivo antioxidant enzyme inductions of tofu.

Keywords: Isoflavones; antioxidant activity; soy extract; tofu; SOD; catalase

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History

  • Published In Issue March 23, 2005
  • Received for review August 31, 2004. Revised manuscript received December 26, 2004. Accepted January 19, 2005. Funding for this study was provided by Project ND 1905/2707, North Dakota Soybean Council, and USDA CSREES NRI 2001-10853.

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