Development and validation of a tertiary simulation model for predicting the potential growth of Salmonella typhimurium on cooked chicken.

The growth of Salmonella typhimurium (ATCC 14028) on the surface of autoclaved ground chicken breast and thigh burgers incubated at constant temperatures from 8 to 48 degrees C in 2 degrees C increments was investigated and modeled. Growth curves at each temperature were fit to a two-phase linear primary model to determine lag time (lambda) and specific growth rate (mu). Growth of S. typhimurium on breast and thigh meat was not different. Consequently, secondary models that predicted lag time and specific growth rate as a function of temperature were developed with the combined data for breast and thigh meat. Five secondary models for lag time and three secondary models for specific growth rate were compared. A new version of the hyperbola model and a cardinal temperature model were selected as the best secondary models for lag time and specific growth rate, respectively. The secondary models were combined in a computer spreadsheet to create a tertiary simulation model that predicted the potential growth (log10) increase) of S. typhimurium on cooked chicken as a function of time and temperature. Probability distributions and simulation were used in the tertiary model to model the secondary model parameters and the times and temperatures of abuse. The outputs of the tertiary model were validated (prediction bias of -4% for lambda and 1% for mu and prediction accuracy of 10% for lambda and 8% for mu) and integrated with a previously developed risk assessment model for Salmonella.