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Effects of Oxalic Acid on Availability of Zinc from Spinach Leaves and Zinc Sulfate to Rats

U.S. Plant, Soil and Nutrition Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Tower Road, Ithaca, New York 14853

Some effects of dietary oxalic acid on availability of zinc from organic and inorganic sources were assessed. Male rats fed zinc-deficient diets with and without added sodium oxalate were orally dosed once with either ⁶⁵Zn-labeled spinach leaves or ⁶⁵Zn-labeled zinc sulfate. Spinach plants (Spinacia oleracea, var. "Winter Bloomsdale") were grown in ⁶⁵Zn-labeled nutrient solutions that contained 0.033, 0.131 or 0.262 ppm zinc. Increasing zinc supply to the plants increased zinc concentration in the leaves. Oxalic acid content in all leaves was about 7% dry weight. Dietary oxalate enhanced the availability of ⁶⁵Zn from zinc sulfate, but had no effect on absorption and retention of ⁶⁵Zn from spinach leaves. Regardless of dietary oxalate levels, absorption and retention of ⁶⁵Zn was greater from spinach leaves than from zinc sulfate. We concluded that endogenous zinc in spinach leaves was readily available to zinc-deficient rats, and that dietary oxalate was not deleterious to zinc availability.

KEY WORDS: • zinc • biological availability • oxalic acid • spinach

Manuscript received 12 October 1976.