Predictive model for growth of Clostridium perfringens at temperatures applicable to cooling of cooked meat

The objective of this study was to develop a model to predict the growth of Clostridium perfringens from spores at temperatures applicable to the cool ing of cooked meat products. The growth medium used was trypticase-peptone- glucose-yeast extract broth. C. perfringens population counts were determin ed at appropriate intervals by plating onto tryptose-sulfite-cycloserine ag ar. C, perfringens growth from spores was not observed at a temperature of 51 degrees C for up to 3 weeks. it was found that, generally for relative g rowth of more than 1/2 log10, the use of the logistic function provided a b etter prediction than the use of the Gompertz function. The two parameters: germination, outgrowth and lag (GOL) time, and exponential growth rate, EG R, were determined using the logistic function. The exponential growth rate s and the reciprocal of the GOL times were fitted to the square root Ratkow sky model, using temperature as the independent variable. Applying multi-va riate statistical procedures, confidence intervals were computed on the pre diction of the amount of relative growth for a given temperature. Closed fo rm equations are developed that allow for predicting growth for a general c ooling scenario and the standard error of the prediction. These equations d epend upon microbiological assumptions of the effect of history of the GOL times for gradual changes in temperature. For example, for cooling from 50 degrees C to 10 degrees C in 8 h, the equations predict a relative growth o f 3.37 with an upper 97.5% confidence limit of 6.73. (C) 1999 Academic Pres s.