Title: Predictive Model for Survival and Growth of Salmonella Typhimurium Dt104 on Chicken Skin During Temperature Abuse Author
Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 1, 2008
Publication Date: February 1, 2009
Citation: Oscar, T.P. 2009. PREDICTIVE MODEL FOR SURVIVAL AND GROWTH OF SALMONELLA TYPHIMURIUM DT104 ON CHICKEN SKIN DURING TEMPERATURE ABUSE. Journal of Food Protection. 72(2):304-314. Interpretive Summary: Marketing of chickens in the United States has changed from predominantly whole chicken in 1965 to predominantly further processed chicken today. Nonetheless, over 50 percent of chickens are still sold whole (11%) or as cut-up parts (43%) with skin. Although skin is a major component of retail chicken and a likely source of Salmonella contamination and transmission, there are no published studies regarding survival and growth of Salmonella on this important tissue of chicken. Models that predict survival and growth of Salmonella are valuable tools for helping assess and manage risk of human illness from this pathogen. However, existing models for Salmonella were developed in sterile food systems without microbial interactions. Since microbial interactions can alter growth of Salmonella, existing models might not accurately estimate risk from chicken contaminated with Salmonella that has been subjected to temperature abuse. In the current study, a predictive model for survival and growth of Salmonella on chicken skin with microbial interactions was developed and properly validated against new data collected with non-kosher and kosher chicken skin. The model developed and validated in this study will provide better predictions of Salmonella survival and growth on chicken than previous models and will save poultry companies money by avoiding unnecessary product recalls and condemnations due to over-prediction of Salmonella risk using older models and at the same time will provide regulatory agencies with a better model for estimating and managing Salmonella risk associated with fresh chicken.
Technical Abstract: To better predict risk of Salmonella infection from chicken subjected to temperature abuse, a study was undertaken to develop a predictive model for survival and growth of Salmonella Typhimurium DT104 on chicken skin with native micro flora. For model development, chicken skin portions were inoculated with 0.85 log CFU of S. Typhimurium DT104 (ATCC 700408) and then stored at 5 to 50C for 8 h. Kinetic data from the storage trials were fit to a primary model to determine lag time (LT), growth rate (GR) and the 95% prediction interval (PI). Secondary models for LT, GR and PI as a function of storage temperature were developed and then combined with the primary model to create a tertiary model for predicting survival and growth of S. Typhimurium DT104 on chicken skin as a function of time and temperature. Performance of the tertiary model was evaluated against dependent data, independent data for interpolation and independent data for extrapolation to kosher chicken skin using an acceptable prediction zone from -1 (fail-safe) to 0.5 (fail-dangerous) log MPN or CFU per skin portion. Survival but not growth of S. Typhimurium DT104 on chicken skin was observed during 8 h of storage at 5 to 20C and at 50C. Growth of the pathogen was observed from 25 to 45C and was optimal at 40C with a lag time of 2.5 h and a growth rate of 1.1 log per h. Variation of pathogen growth, as assessed by PI, increased in a non-linear manner as a function of temperature and was greater for growth conditions than no growth conditions. The percentage of acceptable prediction errors was 82.6% for dependent data, 83.7% for independent data for interpolation and 81.6% for independent data for extrapolation to kosher skin, which all exceeded the performance criterion of 70% acceptable predictions. Thus, it was concluded that the tertiary model provided valid predictions for survival and growth of S. Typhimurium DT104 on both non-kosher and kosher chicken skin.