A greater concentration of oxymyoglobin in meat results in consumer-preferred, bright, cherry-red color of beef. However, exposing meat to air results in conversion of oxymyoglobin into metmyoglobin, and consequently in the formation of very dark-red discoloration of the meat. Several factors, including oxygen partial pressure, influence oxymyoglobin oxidation stability.
High-oxygen modified packaging (HiOx-MAP; 80% oxygen content) is utilized by the meat industry to maximize oxygen partial pressure in beef steaks and increase their shelf-life. As a result, the average shelf-life of steaks in HiOx-MAP is 10-12 days compared to 5-7 days in PVC/atmospheric oxygen partial pressure (20% oxygen) at 4°C. Steaks aged for 7-14 days and packaged in HiOx-MAP show less discoloration, but more lipid oxidation than PVC packaged steaks aged for the same period. This raises a question regarding the preservative effects of HiOx-MAP, because high-oxygen content increases lipid oxidation products, and these compounds are known to stimulate oxymyoglobin oxidation.