Proteolytic Clostridium botulinum growth at 12–48°C simulating the cooling of cooked meat: development of a predictive model

The objective of this study was to develop a model to predict the germination, outgrowth and lag (GOL), and exponential growth rates of Clostridium botulinum from spores at temperatures (12–48°C) applicable to the cooling of cooked meat products. The growth medium, Reinforced Clostridial medium (RCM) supplemented with oxyrase enzyme to create suitable anaerobic conditions, was inoculated with approximately 4 log₁₀spores ml⁻¹. Clostridium botulinum populations were determined at appropriate intervals by plating onto RCM. Clostridium botulinum growth from spores was not observed at temperatures <12°C or >48°C for up to 3 weeks. Growth curves were determined by fitting Gompertz functions to the data. From the parameters of the Gompertz function the growth characteristics, GOL times and exponential growth rates were calculated. These growth characteristics were subsequently described by Ratkowsky functions using temperature as the independent variable. Closed form equations were developed that allow for predicting relative growth for a general cooling scenario. By applying multivariate statistical procedures, the standard errors and confidence intervals were computed on the predictions of the amount of relative growth for a cooling scenario. The predictive model is capable of predicting spore outgrowth and multiplication for general cooling scenarios, for suitable but un-verified mathematical assumptions, and should aid in evaluating the safety of cooked products after cooling.