Utilization of the iron of egg yolk for hemoglobin formation by the growing rat
Morris, E.R.; Greene, F.E.
Journal of Nutrition 102(7): 901-908
1972
ISSN/ISBN: 0022-3166 PMID: 5064280 Document Number: 54798
The maintenance of Hb in the growing rat was used as a bioassay index to estimate the relative biological value (RBV) of the Fe in egg yolk. Weanling rats were given a purified diet based on casein that contained a reference salt or egg yolk as Fe source. The response to ferrous ammonium sulphate as the reference Fe compound was set at 100. The RBV for different egg yolk preparations was: spray dried 20, raw 29, cooked 32 and whole egg 30. In addition to the 23 mg/kg in the basal diet 50 mg Cu/kg produced only a slight increase in Hb response. The yolk diets contained about 0.2% more P than the reference diet, but the addition of this amount of P did not supress the response to the reference salt. Ascorbic acid at 0.125% of the diet increased the RBV of 20 mg/kg yolk Fe to 100 and as little as 0.03% resulted in a significant rise in Hb. Other reducing agents without complexing potential did not improve the RBV of yolk Fe, but those with complexing potential did. Gel permeation chromatography experiments in vitro showed that ascorbic acid frees the Fe from the yolk phosphoprotein. The chemical nature of food Fe is a determining factor in its biological utilisation.