Determination of zinc availability in foods by the extrinsic label technique

Abstract

The absorption of intrinsic ⁶⁵Zn and extrinsic ⁶⁵Zn from corn and liver was measured in rats. No significant difference between the absorption of intrinsic- and extrinsic-label was observed. These results indicate that endogenous zinc and exogenous ⁶⁵Zn enter a common pool prior to being absorbed from the intestine. Since extrinsic ⁶⁵Zn enters a common pool with intrinsic zinc, whole-body absorption of extrinsic ⁶⁵Zn can be used to obtain an accurate estimate of the availability of zinc in food. The availability of zinc in human breast milk, in cow's milk, in infant formulas, and in reconstituted dry milk was analyzed by use of the extrinsic label. The zinc in human breast milk was most available (59%) while the zinc in the infant formulas was the least available (26 to 37%). Zinc from both raw and cooked corn was more available than zinc from either cooked or uncooked rat liver.