Date of Award:

1991

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Nutrition and Food Sciences

Advisor/Chair:

Charles E. Carpenter

Abstract

Studies were undertaken to investigate if gastric acidity and iron chelation to a meat component enhance nonheme iron absorption. Cereal meals, with and without added proteins, were gavaged into iron-deficient rats. The role of iron chelation was investigated by adding sodium phytate, an iron chelator implicated with decreased iron absorption, to the meals. The role of gastric acidity was investigated by treating the rats with cimetidine, which inhibits gastric acid production. In rats with normal acid production, beef, pork and chicken enhanced iron absorption when phytate had been added to the meals, suggesting a role for chelation in meat enhancement of iron absorption. However, the enhancement by beef and pork was insignificant in cimetidine-treated rats given the cereal + phytate meals, indicating that gastric acid production also plays a role in meat enhancement of iron absorption. Fish and egg white were sometimes inhibitory to iron absorption and, therefore, did not fit the pattern of enhancement demonstrated by beef, pork, and chicken. In a separate experiment, gastric acidity was not directly altered by the protein source included with cereal meals. No significant effects of the various proteins on iron absorption from cereal + phytate meals were observed in a final experiment involving iron-replete rats. In vitro iron solubilizing capacity of beef, pork, chicken, and egg white was positively correlated with enhanced iron absorption by iron-deficient rats.

Studies were performed to 1) investigate if ferric iron bound in complex with iron-solubilizing meat components is absorbable, 2) compare the relative iron-solubilizing capacity of meats, and 3) investigate the physicochemical and compositional characteristics of the meat components responsible for the iron solubilizing capability of meat. Iron-solubilizing components of beef were isolated from pH 2 HCl homogenates into dialysis bags (MWCO, 6-8 K). Radiolabelled iron complexes were then generated using ferric iron and either the ILC (isolated low-molecular-weight components) from undigested beef or ascorbate. The bioavailabilities of radioiron in these complexes or as ferric iron were measured as radioiron absorption into the blood one hour after injection into ligated duodenal loops of rats. Iron absorption values were ascorbate-ferrous complexes > beef ILC-ferric complexes > ferric iron (p < .05). In separate experiments, ILC from 0.1 g of various dietary protein sources (beef, pork, chicken, fish, or egg white) were added to 400 μg ferric iron in pH 2 HCl, the pH raised to 7.2, and soluble iron determined in the supernatant after centrifugation at 2,500 g for 10 min. Iron solubilizing capabilities of ILC were pork > beef > chicken > fish > egg white (p < .05). In a final series of experiments, the compositional and physicochemical characteristics of the ILC from the various dietary proteins were investigated.

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