ARS | Publication request: Predictive model for growth of Clostridium perfringens during cooling of cooked uncured meat and poultry

Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 14, 2010
Publication Date: April 10, 2011
Citation: Juneja, V.K., Marks, H.M., Huang, L., Thippareddi, H. 2011. Predictive model for growth of Clostridium perfringens during cooling of cooked uncured meat and poultry. Food Microbiology. 28:791-795.

Interpretive Summary: One of the most common types of food poisoning in the United States is caused by the bacterium, Clostridium perfringens. Illnesses have been traditionally associated with inadequate cooling practices in retail food service operations. Thus, there was a need to determine the time and temperature for cooked uncured meat and poultry products to remain pathogen-free and provide vital data for performing risk assessment on cooked meat. We developed a model that can be used to predict the growth of C. perfringens at temperatures relevant to the cooling of cooked products. The predictive model will be of immediate use to the retail food service operations and regulatory agencies to aid with the disposition of products subject to cooling deviations and therefore, ensure the safety of the cooked foods.

Technical Abstract: Comparison of C. perfringens spore germination and outgrowth in cooked uncured products during cooling for different meat species is presented. Cooked, uncured product was inoculated with C. perfringens spores and vacuum packaged. For the isothermal experiments, all samples were incubated in a water bath stabilized at selected temperatures between 10 – 51C and sampled periodically. For dynamic experiments, the samples were cooled from 54.4 to 27C and subsequently from 27 to 4C for different time periods, designated as x and y hours, respectively. The growth models used were based on a model developed by Baranyi and Roberts (1994), which incorporates a constant, referred to as the physiological state constant, q0. The value of this constant captures the cells’ history before the cooling begins. To estimate specific growth rates, data from isothermal experiments were used, from which a secondary model was developed, based on a form of Ratkowsky’s 4-parameter equation. The estimated growth kinetics associated with pork and chicken were similar, but growth appeared to be slightly greater in beef; for beef, the maximum specific growth rates estimated from the Ratkowsky curve was about 2.7 log cfu/h, while for the other two species, chicken and pork, the estimate was about 2.2 log cfu/h. Physiological state constants were estimated by minimizing the mean square error of predictions of the log 10 of the relative increase versus the corresponding observed quantities for the dynamic experiments: for beef the estimate was 0.007, while those for pork and chicken the estimates were about 0.014 and 0.011, respectively. For a hypothetical 1.5 h cooling from 54C to 27C and 5 h to 4C, corresponding to USDA-FSIS cooling compliance guidelines, the predicted growth (log of the relative increase) for each species was: 1.29 for beef; 1.07 for chicken and 0.95 log for pork. However, it was noticed that for pork in particular, the model using the derived q0 had a tendency to over-predict the relative growth when the observed small amounts of relative growth, and under-predict the relative growth when there was observed large relative growth. To provide more fail-safe estimate, rather than using the derived value of q0, a value of 0.04 is recommended for pork.