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Bioavailability to Rats of Iron and Zinc in Wheat Bran: Response to Low-Phytate Bran and Effect of the Phytate/Zinc Molar Ratio¹

Vitamin and Mineral Nutrition Laboratory, Nutrition Institute, Human Nutrition Center, Science and Education Administration, U.S. Department of Agriculture, Beltsville, MD 20705

Low-phytate wheat bran was produced by enzymatic hydrolysis and extraction. Rat bioassay methods were utilized to determine bioavailability of iron and zinc in the low-phytate brans and to study the effect of dietary phytate/zinc molar ratio on zinc bioavailability when the phytate source was bran. Endogenous phytase activity hydrolyzed 80–100% of the phytate when wheat bran was incubated in water overnight. The relative biological values of the iron in raw bran and phytate-free bran were 98 and 113, respectively, compared to 100 for ferrous ammonium sulfate in a hemoglobin repletion assay. Low-phytate brans with phytate/zinc molar ratios of 8 or less were equivalent to zinc sulfate as dietary sources of zinc for growth of rats. Rats fed diets that contained wheat bran with zinc sulfate added to reduce the dietary phytate/zinc molar ratio from 40 or 50 to 20 grew at the same rate as rats fed a phytate-free diet, but femur zinc values were lower than those in the reference group. Gel filtration chromatography of extracts of raw and low-phytate brans suggested that zinc might be associated with phytate in wheat bran.

KEY WORDS: • zinc bioavailability • iron bioavailability • dephytinized wheat bran

¹ Presented in part at the 61st and 62nd annual meeting of Federation of American Societies for Experimental Biology (Fed. Proc. 36: 1101, 1977, 37: 585, 1978) and the 10th National Conference on Wheat Utilization Research, Tuscon, AR, 16–18 Nov. 1977, ARM-W-4 (Saunders, R. M. ed.) pp. 51–62, Office Regional Administrator for Federal Research, SEA, USDA, Berkeley, CA 94705.

Manuscript received 11 February 1980.