Effects of Heat and Iron Fractions on Lipid Oxidation in Meat.

Size exclusion (SE) and hydrophobic interaction (HIC) high performance liquid chromatography (HPLC) methods were developed for determining hemoglobin, myoglobin, and total pigments in beef and chicken. Hemoglobin and myoglobin in beef, but not in chicken, were separated by HIC with minimum detectable levels of 0.187 and 0.085 $\mu$g/$\mu$l, respectively. Determination of total pigment by SE-HPLC (minimum detection of 0.001 $\mu$g/$\mu$l) was more sensitive than with spectrophotometric assay. The effects of heat at 55$\sp\circ$C, 70$\sp\circ$C, 85$\sp\circ$C, and 100$\sp\circ$C on the distribution of iron in six fractions (water-soluble, water-insoluble, diffusate, hematin, total heme, and ferritin) in beef and chicken muscles were determined. Iron content decreased (p $\u3c$ 0.05) in water-soluble fractions and increased (p $\u3c$ 0.05) in water-insoluble fractions as temperature increased to 100$\sp\circ$C. The content of heme iron was decreased more from 55$\sp\circ$C to 85$\sp\circ$C than from 27$\sp\circ$C to 55$\sp\circ$C or 85$\sp\circ$C to 100$\sp\circ$C. The increase in the amount of diffusate iron appeared to be less than the decreased amount of heme iron at each heating temperature level. As temperature increased, hematin iron content was increased (p $\u3c$ 0.05) and ferritin iron content was decreased (p $\u3c$ 0.05). More ferritin iron was decreased (p $\u3c$ 0.05) at temperature of 70$\sp\circ$C than at 55$\sp\circ$C. The catalytic abilities of heat at 55$\sp\circ$C, 70$\sp\circ$C, 85$\sp\circ$C, and 100$\sp\circ$C and nine forms of iron (water-extractable iron, diffusate iron, non-diffusate iron, hematin, Hb, Mb, ferritin, FeCl$\sb2$ and FeCl$\sb3)$ on lipid oxidation in water-extracted meat residues (WR) and solvent-extracted fat emulsion (FE) of beef and chicken muscles were studied. Heat and different forms of iron promoted lipid oxidation (p $\u3c$ 0.05) in WR and FE for both species. The catalytic abilities of the same forms of iron were different in WR and FE. All forms of iron catalyzed lipid oxidation in WR, however, ferritin, FeCl$\sb2,$ or FeCl$\sb3$ did not increase lipid oxidation in FE. Heme iron was the major catalyst of lipid oxidation in FE, while both heme iron and iron in the low molecular weight fractions (diffusate iron) had high catalytic activity for lipid oxidation in WR