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Reduction of Phytic Acid in Soybean Products Improves Zinc Bioavailability in Rats¹

J. R. Zhou, E. J. Fordyce², V. Raboy^3,, D. B. Dickinson^*, M.-S. Wong⁴, R. A. Burns and J. W. Erdman, Jr.⁵

Division of Nutritional Sciences and Department of Food Science ^* Department of Horticulture, University of Illinois, Urbana, IL 61801 Mead Johnson Research Center, Evansville, IN 47721

The inhibitory effect of phytic acid in soybean products on zinc bioavailability was evaluated in two experiments in rats. In Experiment 1, soybean flours containing different natural phytic acid levels produced by sand culture techniques that limited phosphorus during growth of the soybean plants were formulated into diets. The rats fed a higher phytic acid level diet had lower food intake, depressed weight gain, and lower tibia zinc gain (P < 0.05). A negative, linear relationship between tibia zinc gain and dietary phytic acid level was found. In Experiment 2, two commercially produced soybean isolates containing either normal phytic acid level or a reduced level were formulated into diets. Slope ratio analysis revealed that relative zinc bioavailability from phytic acid-containing soybean isolate-based diets was significantly reduced (P < 0.05) compared with control diets. Reduced phytic acid soybean isolate-containing diets resulted in a significant increase of zinc bloavailability compared with normal phytic acid diets (P < 0.01). These results coupled with other reports indicate that phytic acid is the primary inhibitory factor in soybean products that results in reduced zinc bioavailability and that phytate reduction in soybean protein increases zinc bioavailability.

KEY WORDS: • zinc • bioavailability • rats • soybean protein • phytic acid

¹ Supported by a University of Illinois Experimental Station Hatch Grant (#5310) and Mead Johnson.

² Current affiliation: Champlain Ind. Ltd., Laguna Niguel, CA 92656.

³ Current affiliation: USDA/Agricultural Research Service and Montana State University, Bozeman, MT 59717.

⁴ Current affiliation: Department of Human Nutrition and Nutritional Biology, University of Chicago, Chicago, IL 60637.

⁵ To whom correspondence should be addressed.

Manuscript received 2 January 1992. Revision accepted 3 August 1992.

This article has been cited by other articles:

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