Purpose: The objective of this study was to use a predictive microbiology approach to assess the impact of freezing on the survival and growth of Salmonellaon chicken.
Methods: This was accomplished by evaluating a USDA, ARS, Pathogen Modeling Program (PMP) Model for survival and growth of Salmonella on chicken skin for its ability to predict survival and growth of Salmonella on chicken skin that was frozen for 6 days at -20 °C and then stored at 5 to 50°C for 8 h. Experimental methods used to collect data for model development were the same as those used to collect data for Salmonellasurvival and growth following frozen storage; this was done to provide a valid comparison of observed and predicted values. Residuals from individual survival and growth curves were evaluated using the Acceptable Prediction Zone (APZ) Method.
Results: The proportions of residuals in an acceptable prediction zone (pAPZ) from -1 log (fail-safe) to 0.5 log (fail-dangerous) were acceptable (pAPZ > 0.682) for all survival and growth curves; the overall pAPZ for the test data was 0.846 (154/182). However, there was evidence that freezing injured Salmonella as the mean residual was -0.3 log under growth conditions, which was different (P< 0.05) from zero or the mean residual predicted by the PMP model.
Significance: Findings of this study indicated that the PMP model developed with uninjured Salmonella provided valid predictions of survival and growth of Salmonella injured by a previous history of frozen storage. Validation of predictive models for extrapolation to independent variables not included during model development (e.g., previous frozen storage) can save time and money by identifying conditions for which new models are not needed.