Temperature and pH dependence of the autoxidation rate of bovine, ovine, porcine, and cervine oxymyoglobin isolated from three different muscles--Longissimus dorsi, Gluteus medius, and Biceps femoris.

This study examined the temperature and pH dependence of the in vitro autoxidation rate of bovine, ovine, porcine, and cervine oxymyoglobin that had been isolated and purified from three muscles of different oxidative stability--Longissimus dorsi, Gluteus medius, and Biceps femoris. To avoid obtaining unreliable estimates of autoxidation rate as has occurred in many previous studies, in this study, precautions were taken to eliminate the effects of freezing, chemical reduction with hydrosulfite, and contaminating metal ions on the reaction rate. When these precautions were taken, the rate constants for the different myoglobins studied were similar to each other but were 2-7-fold lower, and the Ea (activation energy) was 20-100% higher than that reported in most previous studies. The type of muscle the myoglobin was isolated from had no effect on the reaction rate or the Ea; however, the species did have a significant effect (p < 0.05) with porcine myoglobin having a 10% lower reaction rate and a 20% lower Ea than myoglobin from the other species. Increasing the reaction pH from 5.50 to 6.50 produced an exponential increase in reaction rate but only a small curvilinear change in Ea that had a maximum at pH 6.00.