Carbon-13 and proton NMR studies of post-mortem metabolism in bovine muscles

Abstract

Proton and carbon-13 NMR was used to investigate post-mortem metabolism in bovine muscles at 26°C during the first 10h after slaughter. WALTZ-16 decoupling was used to eliminate the proton couplings in the 13C spectra and the ‘jump and return’ pulse sequence was used to suppress the water resonance in the 1H-NMR experiments. With carbon-13 NMR the glycogen breakdown and the lactate development could be followed. This was compared with the lactate, creatine and phosphocreatine development as measured by proton NMR. The intracellular pH was estimated from the chemical shift of the abundant dipeptide, carnosine, as measured in the 1H- and 13C-NMR spectra. These were compared with similar measurements obtained earlier using phosphorus-31 NMR. The three independently determined pH profiles were in excellent agreement with one another, as well as with results obtained with the standard iodoacetate extraction method. In the course of these studies we observed that the post-mortem metabolism in cow and heifer was slow and that it took four more hours to complete compared to bull or young bull. After 10 h the pH was 5·9 in bull and 6·1 in cow. Phosphocreatine had completely disappeared after 3·5 h in bull samples while the lactate continued to increase even after 10h. The curves obtained by carbon-13 and proton NMR for the increase in lactate during the first 10 h post mortem were very similar. Moreover, plots for the increase in the lactate level versus the intracellular pH decrease showed a linear relationship, indicating that anaerobic glycolytic activity is the main determining cause for the intracellular pH decrease. Various other parameters, such as the ratio of unsatirated to saturated fatty acid side chains and the presence of amino acids and taurine, could be measured from the in vivo carbon-13 NMR spectra. However, no gross changes occured in any of these parameters during the first 10 h post mortem.