44C-26 |
The antioxidant activity of soy extracts containing isoflavones |
K. C. CHANG, Dept. of Cereal Science, North Dakota State Univ., Ind Ag Comm Ctr 322, Fargo, ND 58105, J. Liu, Dept. of Microbiology, Univ. of Minnesota, Minneapolis, MN 55455, and G. Su, Dept. of Food & Nutrition, North Dakota State Univ, Ind Ag Comm Ctr, Rm. 370, Fargo, ND 58105.
Animal studies indicate that isoflavones have antioxidant characteristics. However, most studies used a high level of purified isoflavones and the feeding period was short. However, the isoflavone content in soy foods consumed is relatively low as compared to the levels used in the studies fed purified isoflvaones. Therefore, long term in vivo studies at low concentrations are needed. We conducted a long-term isoflavone feeding test on rats. Crude soy extract containing isoflavones (50, 150 and 250 ppm) were tested for antioxidant activity in sunflower oil. The in vivo analysis was carried out by determining SOD and catalase activities in intestine, kidney, liver, lung, and skin after feeding for 8, 16, and 24 weeks. Soy isoflavone extracts showed a strong in vitro antioxidant activity. At lower isoflavone concentration, there was a dose-dependent response. When the isoflavone content was relatively high (>150ppm), the in vitro antioxidant activity reached a plateau. Feeding a 250ppm isoflavone diet significantly increased the activities of SOD in liver after 8 weeks, in lung after 16 weeks, and in intestine, kidney, lung, and skin after 24 weeks, the activities of catalase in intestine and liver after 16 weeks, in intestine, kidney and liver for 24 weeks. Feeding 150ppm isoflavones resulted in elevated SOD activity in intestine after 24 weeks, and increased catalase activities in intestine, liver, and skin after 16 weeks, and in intestine, kidney and liver after 24 weeks. Feeding 50 ppm diet had no significant effects. Therefore, isoflavones have antioxidant activities in vivo, but are effective only at a relatively higher concentration, and for a longer time period. Although isoflavones had in vitro antioxidant activities, the in vivo enzyme activities increased. Isoflavones might have their in vivo antioxidant effects by either inducing the expression level or modifying the enzyme activity rather than exerting scavenging effect directly.
Session 44C, Fruit & Vegetable Products: Chemistry
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