Predictive model for growth of Clostridium perfringens during cooling of cooked cured chicken

Estimates of the growth kinetics of Clostridium perfringens from spores at temperatures applicable to the cooling of cooked cured chicken products are presented. A model for predicting relative growth of C. perfringens from spores during cooling of cured chicken is derived using a nonlinear mixed effects analysis of the data. This statistical procedure has not been used in the predictive microbiology literature that has been written for microbiologists. However, recently software systems have been including this statistical procedure. The primary growth curves, based on the stages of cell development, identify two parameters: (1) germination, outgrowth, and lag (GOL) time, or lag phase time; and (2) exponential growth rate, egr. The mixed effects model does not consider GOL and egr as constants, but as random variables that would, in all likelihood, differ for different cooling events with the same temperature. As such, it is estimated that the egr, for a given temperature, has a CV of approximately 19%. The model obtained by the mixed effects model is compared to the one obtained by the more traditional two-stage approach. The estimated parameters from the derived models are virtually the same. The model predicts, for example, a geometric mean relative growth of about 9·4 with an upper 95% confidence limit of 21·3 when cooling the product from 51°C to 12°C in 8 h, assuming log linear decline in temperature with time. C. perfringens growth from spores was not observed at a temperature of 12°C for up to 3 weeks.