Submitted to: Journal of Food Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/13/2007
Publication Date: 5/1/2007
Citation: Huang, L. 2007. Numerical Analysis of Survival of Listeria monocytogenes during In- Package Pasteurization of Frankfurters by Hot Water Immersion. Journal of Food Science. 72(5):E285-E292. Interpretive Summary: For decades the design and evaluation of thermal processes has been based on a traditional method, or the General method, which calculates the total lethality according to the thermal inactivation kinetics and the temperature history at the coldest point of the food. For thermally conductive foods this method has shown to be "conservative", which leads to overcooking and less desirable qualities of products. This research proposed and validated a more accurate method for calculating the lethality during thermal processing of solid foods. If adopted by the industry, the new method may result in reduced cooking time and improved product qualities.
Technical Abstract: The objective of this research was to develop a more accurate method to analyze and calculate the inactivation of L. monocytogenes in packaged frankfurters during post-lethality hot water immersion heating and subsequent cooling processes. Finite difference analysis with implicit scheme was used to simulate the heat transfer process during in-package pasteurization of frankfurters. A new volumetrically-distributed simulation method was developed to calculate the lethality of thermal processing. The new simulation method was validated using frankfurter packages inoculated with a four-strain cocktail of L. monocytogenes. Experimental results showed that the numerical analysis by the finite difference method could accurately simulate the heat transfer process during heating and cooling of frankfurter packages. The simulated temperatures on the surface or in the middle of the package agreed very closely with the experimental observations. Using the simulated temperature distribution in the packages, the new simulation method, based on the volumetric distribution of bacteria in the packages, could accurate predict the reduction in the bacterial counts and were o average within 0.3 log(CFU/g) difference from the experimental observations. The General Method systematically underestimated the bacterial reductions by approximately 0.9 log(CFU/g), indicating that the thermal processes designed according to this method was indeed more conservative than necessary. Since the new simulation method is more precise than the General Method, thermal processes designed by the new method would be more accurate and shorter than the processes designed by the General Method. Thus, this method can be used to thermal processes that avoid unnecessary heating such as during in-package pasteurization of frankfurters.