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Isolation of Monoferric Phytate from Wheat Bran and its Biological Value as an Iron Source to the Rat¹

Vitamin and Mineral Nutrition Laboratory, Nutrition Institute, Beltsville Agricultural Research Center, USDA, ARS, Beltsville, Maryland 20705

The objectives of the study were to isolate and chemically characterize the iron in wheat and to determine the biological availability to the rat of the iron as the purified complex(es). Hard wheat bran contained no butanol extractable or water extractable iron, but approximately 60% of the iron was extracted by 1 to 1.2 M NaCl or ammonium acetate solution. This salt extractable iron complex was purified and identified as monoferric phytate. The purified monoferric phytate was soluble in water. Synthetic monoferric phytate was prepared from sodium phytate and ferric chloride and determined to have spectral characteristics and gel filtration chromatography behavior identical to the complex isolated from wheat bran. The butanol-water-salt extracted bran residue contained no detectable phytate and an as yet uncharacterized form of iron. The biological availability of the iron to the rat was determined by a hemoglobin depletion-repletion bioassay. The relative biological value of the iron as monoferric phytate, either isolated from wheat bran or the synthetic product, was equal to the reference compound, ferrous ammonium sulfate. In contrast, the biological availability of the iron in the bran residue was significantly lower and the low biological availability of an insoluble form of ferric phytate was confirmed. It is concluded that the major portion of the iron in wheat is monoferric phytate and has a high biological availability to the rat. Monoferric phytate in bran may be bound to cationic sites of proteins or other cellular components and utilization of the iron may be through solubilization of the monoferric phytate by ion exchange type mechanism rather than by hydrolysis of the phytate as has been postulated.

KEY WORDS: • monoferric phytate • iron • biological availability • phytate • wheat

¹ Presented in part at Second International Symposium on Trace Element Metabolism in Animals, Madison, Wisconsin, June 1973. Morris, E. et al. in Trace Element Metabolism in Animals-2, Hoekstra, W. et al. ed., pp. 506–508. University Park Press, Baltimore, Md. and the 59th Annual Meeting of American Institute of Nutrition, Atlantic City, N.J., April 1975. Federation Proc. 34, 923 (Abstr.).

Manuscript received 9 December 1975.

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