Post mortem energy metabolism and pH development in porcine M. longissimus dorsi as affected by two different cooling regimes. A (31)P-NMR spectroscopic study

(31)P-NMR spectroscopy was carried out on M. longissimus dorsi samples chilled by two different cooling profiles corresponding to commercial batch and tunnel chilling. The half-life of post mortem phosphocreatine (PCr) degradation was found to be significantly less in muscle samples exposed to tunnel chilling (rapid) compared with muscle samples exposed to batch chilling (soft) conditions, while no difference in the post mortem ATP degradation was found. Moreover, the post mortem pH development in the muscle samples differed considerably between the two cooling regimes. A maximum difference of approx. 0.25 pH units between the two cooling profiles was observed around 150 min post mortem. Theoretical calculations of the registered pH difference between rapid and soft chilling of muscle samples revealed that the temperature effect on the buffer capacity of muscle is the major determining factor in the detected difference in intracellular pH between the two cooling profiles, while any contribution from a temperature-induced delayed progress in the lactate formation post mortem seems negligible. Moreover, calculations on the effect of the registered pH difference between rapid and soft chilling of muscle samples resemble a 2.5 times greater denaturation of myosin in samples which were chilled softly compared with samples chilled more rapidly. Finally, the relationship to the functionality of meats from soft and rapid chilled pork carcasses is discussed.