H-1-NMR STUDY OF BOVINE MYOGLOBIN AUTOXIDATION - INFLUENCE OF MUSCLE-TYPE AND TIME POSTMORTEM

H-1 NMR spectroscopy was used to determine first order rate constants at four temperatures (300, 304, 308, 312 K) and activation energies of the autoxidation reaction for oxymyoglobin. The haeminic pigment was purified from two bovine muscles with different colour stabilities (ps oas major (PM) and longissimus lumborum (LL)) at 2 h (day 0) and 192 h (day 8) post mortem. To characterize this autoxidation reaction, we h ave focused attention on the time-temperature dependent disappearance of the Val-E11 methyl group signal. This study showed that, whatever t he time post mortem, although the myoglobin autoxidation rate was grea ter for PM than for LL muscle, the activation energies were similar. I t was also worth noting that, in the range 300-312 K, the average rati o of autoxidation rate constants between day 8 and day 0 was near 1.6 for the two muscles studied. It is reasonable to think that oxidative processes developed during 8 days meat storage have led to a structura l change within the cavity of the heme pocket of the myoglobins. Moreo ver, only one orientation of the porphyrin within the heme pocket was noted for the two muscles studied.