Application of an exponential model to early postmortem bovine muscle pH decline

An exponential decay equation was used to describe the decline of pH in bovine M. longissimus thoracis et lumborum (LTL) muscle postmortem. Goodness of fit of the equation was tested by convergence of model criterion and contrasting predicted against expected pH values of LTL muscles from 24 Bos taurus steer carcasses measured 40, 60, 80, 120, 185 and 1440 min after stunning. The model was fitted to pH values measured, as well as to the measured pH values adjusted to arbitrary constant temperatures of 10, 20 or 30°C. The model failed to converge for 46% of the muscles sampled in the data sets with measured pH. The model converged for 100% of the muscles with pH values adjusted to 10, 20 or 30°C. Limits of agreement, heteroscedasticity and intraclass correlation analyses showed little difference in the fit of the model to pH values adjusted to either 10, 20 or 30°C. Fitting this model to pH data adjusted to 20°C will enable comparison of rates of pH decline between muscles of different temperatures postmortem or laboratory homogenates and facilitate relation of pH decline rate to aspects of beef quality.