A note on the suitability of an exponential equation to characterize pH decline corrected for muscle temperature in bovine muscle early post mortem.

Identifying rates of pH and temperature decline associated with bovine M. longissimus thoracis et lumborum (LTL) tenderness would assist beef carcass processors to produce a high quality product. An exponential decay equation was used to describe the early post mortem declines of pH values adjusted to 20 °C and their concomitant temperature data from 371 bovine LTL muscles. Approximately 10% of the muscles in the database exhibited non-exponential pH decline post mortem and the model did not converge for these muscles. For convergent muscles, the model predicted pH values homoscedastically with no significant bias. Limits of agreement analysis showed that the model predicted the adjusted pH value within 0.14 pH units. Prediction error was evenly distributed and the intra-class correlation coefficent was high (r(I)=0.98). When applied to the muscle temperature data, the exponential equation predicted temperature values heteroscedastically. These results indicated that this exponential equation characterised the post mortem pH decline in LTL muscle sufficiently well for researchers to use the exponential constant (k) of decay to describe this decline with time or muscle temperature. The equation was not appropriate for describing the decline of muscle temperature with time post mortem in this data set.