Predicting the growth of Escherichia coli on displayed pork

Samples of sterile pork fat or muscle tissue were inoculated with logarithmic phase cultures of Escherichia coli and were incubated in a display case at positions where they experienced average temperatures of 3.5, 6.0, 6.9, 8.0, 9.7 or 11.4 degrees C. The temperature history of the tissue at each position was recorded. During incubation for up to 7 days, samples of each tissue were removed daily from each position for enumeration of E. coli and growth of E. coli at each position at each of those times was estimated by integrating the temperature history of the tissue with respect to a model describing the dependency on temperature of the aerobic growth of E. coli. When temperatures fluctuated above 7 degrees C for periods <1 h, no growth of E. coli occurred on fat or muscle tissue although growth would be predicted by the model. When temperatures fluctuated above 7 degrees C for periods >1 h, the predicted growth and that observed on fat tissue were similar. However, growth on muscle tissue occurred only when temperatures fluctuated above 9 degrees C for lengthy periods, and then only after a lag of about 4 days when temperatures remained mainly below 12 degrees C. When temperatures fluctuated above 12 degrees for lengthy periods the predicted growth and that observed on both fat and muscle tissues were similar. Accurate prediction of the growth off. coli on meat which experiences temperatures that fluctuate below 7 degrees C will require the development of models to predict the lag before growth of E. coli on fat or muscle tissues during periods at growth-permitting temperatures.