ARS | Publication request: Validation of a predictive model for survival and growth of Salmonella Typhimurium DT104 on chicken skin for extrapolation to a previous history of frozen storage

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 18, 2013
Publication Date: N/A

Interpretive Summary: The Predictive Microbiology Information Portal is a USDA-sponsored website (http://portal.arserrc.gov/) that seeks to educate large and small food companies about proper use of predictive models for improving microbiological safety of food. Included in the website is the USDA, Agricultural Research Service (ARS), Pathogen Modeling Program (PMP), which is a computer software application that contains predictive models for cross-contamination, survival, growth and death of foodborne pathogens. Validation of predictive models is an important step in model development because it increases confidence in using them to make important food safety decisions. In addition, validation of models for extrapolation to a variable not included in model development is important because it saves time and money by identifying conditions for which new models are not needed. In the present study, a validated PMP model for survival and growth of Salmonella on fresh chicken was validated for predicting survival and growth of Salmonella on frozen chicken. Thus, investing additional time and money into development of a new model for frozen chicken was avoided.

Technical Abstract: A predictive model for survival and growth of Salmonella Typhimurium DT104 on chicken skin was evaluated for its ability to predict survival and growth of the same organism after frozen storage for 6 days at -20 C. Experimental methods used to collect data for model development were the same as those used to collect data for survival and growth following frozen storage; this was done to provide a valid comparison of observed and predicted values. Residuals (observed log counts minus predicted log counts) from individual survival and growth curves were evaluated using an acceptable prediction zone from -1 log/portion (fail-safe) to 0.5 log/portion (fail-dangerous). The proportion of residuals in the acceptable prediction zone (pAPZ) was acceptable (pAPZ 0.682) for all survival and growth curves with an overall pAPZ for extrapolation to previous frozen storage of 0.846 (154/182). However, there was evidence that frozen storage injured S. Typhimurium DT104 as most residuals were below zero indicating reduced survival and growth. Findings of this study indicate that the predictive model provided valid predictions of survival and growth of S. Typhimurium DT104 following frozen storage for 6 days at -20 C.