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The Effect of Heating Chicken Muscle on Formation of Bioavailable Froms of Iron

Muscle foods/meat enhances bioavailability of non-heme iron form the diet. This effect is generally thought to be due to production of peptides, by gastro-intestinal digestion, which reduces/chelate the iron in upper intestine. Dialyzable iron is widely used as an in-vitro indicator of iron bioavailability, and with few exceptions, correlates well with human studies. Human studies have used cooked meat to test the effect on iron, but little attention has been given to the effects of cooking. We studied the effect of heating chicken muscle on the production of dialyzable iron. Chicken breast muscle was homogenized and heated to the temperatures in the range of 130-195oF. The concentration of amino acid binding residues was determined in the heated samples. The samples were then mixed with ferric iron and digested with pepsin and pancreatin. Heating chicken muscle caused a large drop in sulfhydryl (-SH) content and a lesser but significant loss in histidine content, both of which increased progressively with temperature. At 165oF, considered a safe cooking temperature, the loss in –SH and histidine was 75% and 37%, respectively. Changes in dialyzable iron and dialyzable ferrous iron (often considered the best indicator of bioavailability) paralleled the drop in amino acid. Raw uncooked chicken muscle produced about 11 times as much dialyzable iron and 17 times as much dialyzable iron as the control but heating to 165oF reduced the values by 47% and 74% respectively. Heating to 195oF reduced caused a further drop in dialyzable iron values. Our result showed that cooking chicken muscle caused a large decrease in the production of dialyzable iron forms-especially in the ferrous form- and this is correlated with the loss in critical iron binding amino acids.