Irradiation effects on meat color – a review

Color changes in irradiated fresh meat occur because of the susceptibility of the myoglobin molecule, especially the iron, to alterations in the chemical environment and to energy input. The potential for iron electrons to exist in various states makes the environment adjacent to the iron atom particularly vulnerable to the presence of electron-donating compounds and high energy inputs (irradiation). Initial condition of the myoglobin (Fe++O2, Fe+++), modification of oxidation–reduction potential of the tissue, and generation of ligand-forming compounds (CO) from endogenous organic compounds and water are enhanced or suppressed depending on the gas atmosphere, temperature, pH and myoglobin concentration of the system. Generation of stable red pigments or brown pigments which become red over time appears to be due to binding of irradiation-generated reactive oxygen species (O2−) or gasses (CO) which become ligands bound by iron under altered reducing conditions. Rapid generation of large amounts of metmyoglobin when irradiation is conducted in an oxygen-containing environment appears to be an acceleration of the normal process by which myoglobin undergoes oxidation. Generation of green pigments appears to be due to breakdown of the porphyrin integrity and/or formation of sulfmyoglobin. Maintenance of ideal meat color during irradiation can be enhanced by various combinations of pre-slaughter feeding of antioxidants to livestock, optimizing the condition of the meat prior to irradiation, addition of antioxidants, gas atmosphere (MAP), packaging, and temperature control.