Relationship between oxygen concentration, shear force and protein oxidation in modified atmosphere packaged pork.

Pork loins were stored at 5°C for 14 days to investigate the effect of oxygen concentration in modified atmosphere packaging (MAP) on shear force and oxidation of lipids and proteins. The modified atmosphere contained 0 to 80% O2, 20% CO2, and balanced with N2. The results showed that shear force and thiobarbituric acid-reactive substances (TBARS) values increased with increasing oxygen concentration. Protein oxidation when measured as loss of free thiol groups, was greater in meat packaged under oxygen (20-80%). Myosin heavy chain (MHC) cross-linking, another marker of protein oxidation, was greater in MAP with 80% oxygen than 0% and 20% oxygen. Desmin degradation was not affected by the presence of oxygen, suggesting that the mechanism of oxygen-induced toughening of meat is through protein oxidation leading to cross-linking of structural proteins rather than through inactivation of proteolytic enzymes leading to reduced proteolysis.