Predictive Models for Thermal Inactivation of Listeria Monocytogenes on the Surface of Hot Dogs

APPROACH: Strains of L. monocytogenes linked to outbreaks will be grown individually in tryptic soy broth (TSB) and transferred to various conditions to allow cells to adapt to stressed environments prior to inoculating hot dogs. Specifically, cells will be grown under more optimum conditions in TSB, in a hot dog slurry, and suspended in water containing residual sanitizer. Hot dogs will be formulated at a commercial meat-processing company to contain from 10 to 30% fat and combinations of sodium diacetate and sodium lactate as used in industry. A portion of the hot dogs will be sprayed with combinations of sodium diacetate and potassium lactate. Hot dogs will be surface-inoculated individually with the strains of L. monocytogenes, vacuum packaged, and stored at 7\'C before thermal processing. The vacuum packaged hot dogs will be placed into baskets submersed into water baths at 50 to 70\'C. A thermocouple will be placed onto the surface of hot dogs in a central area of selected pouches to monitor come-up, processing and come-down temperatures. Microbial survival curves will be plotted using the log survivors versus heating time and modeling using linear and non-linear approaches where necessary. The models will be integrated into the ARS Pathogen Modeling Program, and the data sets will be archived in ComBase, a relational database of predictive microbiology information available through the Internet. A journal article will be submitted summarizing the results of the studies. A yearly and final report will be submitted to ARS-NPS and NAFS.
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PROGRESS: 2003/09 TO 2006/09<BR>
Progress Report Objectives (from AD-416) The long-term goal of the proposed research is to develop realistic and accurate predictive models for the thermal inactivation of Listeria monocytogenes in processed ready-to-eat meats. The specific objectives are 1) to study and compare thermal inactivation models for L. monocytogenes grown under stress conditions in low and high fat hot dogs (10 to 30%), in conditions to simulate its presence in water and residual sanitizers, and in tryptic soy broth, 2) to compare surface thermal inactivation models over a range of post-processing temperatures relevant to industrial practices for L. monocytogenes in hot dogs made with and without combinations of sodium diacetate and potassium lactate as currently used in the industry, 3) determine thermal inactivation of L. monocytogenes on hot dogs surface-sprayed with different combinations of sodium diacetate and potassium lactate, and 4) to validate the new models against the experimental data for inactivation of L. monocytogenes in hot dogs using the growth medium that represents high and low D-values and sprayed lactate/diacetate formulations. Approach (from AD-416) Strains of L. monocytogenes linked to outbreaks will be grown individually in tryptic soy broth (TSB) and transferred to various conditions to allow cells to adapt to stressed environments prior to inoculating hot dogs. Specifically, cells will be grown under more optimum conditions in TSB, in a hot dog slurry, and suspended in water containing residual sanitizer. Hot dogs will be formulated at a commercial meat-processing company to contain from 10 to 30% fat and combinations of sodium diacetate and sodium lactate as used in industry. A portion of the hot dogs will be sprayed with combinations of sodium diacetate and potassium lactate. Hot dogs will be surface-inoculated individually with the strains of L. monocytogenes, vacuum packaged, and stored at 7\'C before thermal processing. The vacuum packaged hot dogs will be placed into baskets submersed into water baths at 50 to 70\'C. A thermocouple will be placed onto the surface of hot dogs in a central area of selected pouches to monitor come-up, processing and come-down temperatures. Microbial survival curves will be plotted using the log survivors versus heating time and modeling using linear and non-linear approaches where necessary. The models will be integrated into the ARS Pathogen Modeling Program, and the data sets will be archived in ComBase, a relational database of predictive microbiology information available through the Internet. A journal article will be submitted summarizing the results of the studies. A yearly and final report will be submitted to ARS-NPS and NAFS. Significant Activities that Support Special Target Populations 1935-42000-057-03G - This report serves to document research conducted under a General Assistance type of agreement between ARS and Purdue University. Researchers at Purdue University and the ARS Eastern Regional Research Center in Wyndmoor, PA are developing realistic and accurate predictive models for the thermal inactivation of L. monocytogenes in processed RTE meats. This was accomplished by studying and comparing thermal inactivation models for L. monocytogenes grown under stress conditions in low and high fat hot dogs (10 to 30%), in conditions to simulate its presence in water and residual sanitizers, and in tryptic soy broth. This was done by 1) comparing surface thermal inactivation models over a range of post-processing temperatures relevant to industrial practices for L. monocytogenes in hot dogs made with and without combinations of sodium diacetate and potassium lactate as currently used in the industry, 2) by determining thermal inactivation of L. monocytogenes on hot dogs surface-sprayed with different combinations of sodium diacetate and potassium lactate, and 3) by validating the new models against the experimental data for inactivation of L. monocytogenes in hot dogs using the growth medium that represents high and low D-values and sprayed lactate/diacetate formulations. This research supports the Project Plan by producing technologies that can be transferred to food companies, food regulators and risk assessors to design more effective processing controls to minimize the risks of listeriosis. The monitoring activities included phone calls and receipt of written reports.