Response surface models for effects of temperature and previous temperature on lag time and specific growth rate of Salmonella Typhimurium on cooked ground chicken breast.

Response surface models were developed for effects of temperature (16 to 34 degrees C) and previous temperature (pretemperature; 16 to 34 degrees C) on lag time (lambda) and specific growth rate (mu) of Salmonella Typhimurium on cooked ground chicken breast. The primary objective was to determine whether pretemperature is a major factor affecting growth of Salmonella Typhimurium. Growth curves for model development (n = 32) and model testing (n = 18) were fit to a two-phase linear equation that directly estimated lambda and mu. Response surface models for ln lambda and ln mu as a function of temperature and pretemperature were obtained by regression analysis. Lag time and mu of Salmonella Typhimurium were affected by temperature but not pretemperature. Models were tested against data not used in their development. Prediction error (model accuracy) was 13.4% for lambda and 11.3% for mu, whereas the median relative error of predictions (model bias) was -3.0% for lambda and 6.8% for mu. Results indicated that the models provide reliable predictions of lambda and mu of Salmonella Typhimurium on cooked ground chicken breast within the matrix of conditions modeled. In addition, pretemperature (16 to 34 degrees C) is not a major factor affecting growth of Salmonella Typhimurium.