Post-mortem metabolism in fresh porcine, ovine and frozen bovine muscle.

Post-mortem metabolism was followed by phosphorus-31-NMR in muscle samples obtained from freshly slaughtered pigs and lambs. Resonances for creatine phosphate (CP), ATP, inorganic phosphate (Pi) and sugar phosphates (SP) could be discerned and the intracellular pH could be determined from the spectra. The rates of post-mortem metabolism varied in the following fashion: porcine muscle > ovine muscle > bovine muscle. However, the course of post-mortem metabolism was, in all cases, the same. CP disappeared first and then ATP. Simultaneously, Pi increased, while SP remained relatively constant. The intracellular pH decreased to pH 5·5 in all tissues. In a separate set of experiments the post-mortem metabolism during thawing was studied in bovine muscles that had been frozen immediately after slaughter. Again, the same course of post-mortem metabolism was observed, but the thaw shortening was accompanied by an extremely rapid post-mortem metabolism, which was more than ten times as fast as that measured for fresh bovine muscles. The intracellular pH decreased from 7·2 to 5·5 in 45 min. This rapid metabolism started only after the sample ha reached 0°C. Resonances for metabolites were broadened in frozen muscles due to the limited motions that are allowed within the ice lattice.