Effect of a Soluble Fraction of Oil Seed Meals on Uptake of 65Zn from Ca·Mg·65Zn·Phytate Complexes by the Chick

Abstract

The objectives were to relate the uptake of ⁶⁵Zn by the chick from certain fractions of phytate-containing oil seed meals to the varying availability of the meal zinc in vivo, and to delineate conditions in vitro which could account for availability of zinc bound by a casein digest, as compared with zinc bound by phytate. The insoluble Ca·Mg·⁶⁵Zn·phytate complex and the corresponding “soluble fraction” of 61 sesame meal (61 SM); zinc unavailable to the chick, and of Venezuelan sesame meal (VSM); zinc available, were prepared by an in vitro method simulating the chick's initial digestive processes. Inclusion of the soluble fraction of 61 SM with its ⁶⁵Zn·phytate complex did not significantly increase uptake of ⁶⁵Zn by blood, liver or tibiae. Inclusion of the soluble fraction of VSM significantly increased uptake from its phytate complex. It was postulated that VSM contained precursors of substances which form a more stable bond with zinc than does phytate during the digestion process; zinc is available from this complex; 61 SM lacks these precursors. The soluble fraction of soybean meal (SBM) contained about 75% of the extracted zinc; uptake of ⁶⁵Zn from this fraction was comparable to that from ⁶⁵ZnCl₂. Inclusion of the unlabeled SBM fraction with the ⁶⁵Zn·phytate complex of 61 SM or VSM resulted in a significant increase in uptake of ⁶⁵Zn. When equal parts of 61 SM and SBM were fed, inclusion of the SBM prevented appearance of leg abnormalities and caused a significant increase in weight. It was postulated that SBM contained a substance which could render the zinc of an insoluble phytate complex available in vivo. ⁶⁵Zn added to a casein digest was bound at intestinal pH; dialysis to water was low but about 50% of the ⁶⁵Zn dialyzed to blood. Little dialysis of ⁶⁵Zn to blood or water occurred with phytate-containing sesame digest. It is suggested that during the process of digestion in vivo zinc may be bound in the presence of a number of feedstuffs; the avidity with which zinc is taken up by blood components will influence its absorption.