Evaluation of Zinc Availability in Foodstuffs of Plant and Animal Origin

Abstract

Growth response of chicks and rats was used to evaluate the biological availability of zinc in selected cereal grains and animal products. Two sources of protein, soybean and casein-gelatin, were used in the basal low zinc diets and graded levels of ZnCO₃ were added to establish the standard response curve. Thus, the availability values are based on the assumption that 100% of the zinc in ZnCO₃ is available. A plot of weight gain during a 4-week period versus the logarithm of zinc added gave a straight line relationship over the range of 3 to 12 ppm. The 5 to 10 ppm range was used to evaluate the supplements which were added to the basal diets in lieu of carbohydrate. The minimum zinc requirement for chicks and rats fed the soybean protein diets was 19 ppm and for chicks fed the casein-gelatin diet it was 12 ppm. The following biological availabilities were obtained by use of the chick assay: high lysine corn 65%, control corn 63%, rice 62%, wheat 59%, high lysine corn germ 56%, control germ 54%, sesame meal 59%, soybean meal 67%, egg yolk 79%, fish meal 75%, oysters 95%, and nonfat milk 82%. The rat assay gave: high lysine corn 55%, control corn 57%, wheat 38%, rice 39%, egg yolk 76%, nonfat milk 79% and fish meal 84%. In general the zinc in plant seeds was less available than that in animal products, and rats utilized the zinc in plant seeds less well than chicks.