Heating chicken breast muscle reduces the amount of dialyzable iron after extraction and digestion

We studied the effect of heating chicken breast muscle on the amount of dialyzable iron derived from added ferric iron. The chicken was homogenized and heated to temperatures in the range of 130-195°F. The heated muscle was mixed with ferric iron and either extracted with acid or digested with pepsin and pancreatin. Similar amounts of dialyzable iron were observed after extraction and proteolytic digestion; however, digestion led to more dialyzable ferrous iron. Heating caused markedly reduced levels of dialyzable iron and dialyzable ferrous iron both by extraction and digestion. In the range of 130-165°F the losses were due mainly to reduced levels of ferrous iron. At 195°F both ferric and ferrous dialyzable iron levels were markedly reduced (>80%) compared to raw muscle. At 165°F losses in dialyzable iron after extraction were much greater than after digestion. Heating caused progressive losses in sulfhydryl and histidine residues and mostly lowered protein digestibility. Our results demonstrate that heating muscle above 130°F causes losses in dialyzable iron, coincident with (and possibly due to) losses in amino acid residues that reduce and chelate iron. The results suggest that cooking chicken muscle will reduce its ability to promote non-haem iron uptake and that the magnitude of the reduction will tend to increase with increasing temperature.