Date of Award
Master of Science (MS)
Committee Member 1
Fernanda San Martin
Committee Member 2
Non-typhoidal Salmonella is the leading cause of foodborne illness in the United States, resulting in about 20,000 hospitalizations and nearly 380 deaths annually. The meat processing industry has been especially plagued by Salmonella, from meat-inherent sources and more alarmingly, cross-contamination. For ready-to-eat (RTE) meat products specifically, this can cause significant problems in processing facilities ensuring safe product for consumption, resulting in foodborne illness.
The development of standard lethality compliance guidelines by the United States Department of Agriculture Food Safety and Inspection Service (USDA-FSIS) within Appendix A assists processors in confirming that Salmonella is inactivated in RTE beef and poultry products, based on a “worst case” raw product contamination condition. While this is beneficial, means of thermal process validation are limited. However, the identification of five non-pathogenic E. colistrains isolated from cattle may provide a method of validation for processors. Previous studies have investigated the behavior of the isolates individually in response to a variety of microbial interventions, including cooking, fermentation, freezing, refrigerated storage, and antimicrobial treatments as compared to the behavior E. coli O157:H7 as well as Salmonella. Based on the results of these studies, it was sensible to study the behavior of the combined non-pathogenic E. coli isolates in ground beef at varying fat contents under thermal processing conditions compared to Salmonella to determine its potential for use to validate thermal processing. Therefore, the objective of this study was to determine if the non-pathogenic E. coli isolates could be used as a surrogate for a mixed culture of Salmonella as means to validate thermal processing parameters in accordance with Appendix A.
For lower temperatures outlined in Appendix A (130, 135, 140, 145°F (54, 57, 60, and 63°C)), the non-pathogenic E. coli inoculum has significantly different (P < 0.05) decimal-reduction values (D-values), in that they are significantly greater than Salmonella D-values across all five fat content levels (5, 10, 20, 25, 30%). At temperatures greater than 145°F (63°C), no significant differences (P > 0.05) existed between the inoculums across fat content, indicating that the two inoculums were being inactivated at similar rates. These results suggest that the most appropriate use of the non-pathogenic E. coli surrogates would be for predicting, ensuring, and validating thermal processing for the inactivation of Salmonella at lower temperatures, specifically those that fall within the “danger zone” that support rapid bacterial growth (40 - 140°F (4 - 60°C)). Beyond temperature 145°F (63°C), the non-pathogenic E. coli inoculum offers no substantial advantage, as it is being inactivated as rapidly as Salmonella. Due to its prolific growth and high-density yield, the absence of the E. coli inoculum can ensure the inactivation Salmonella at higher thermal processing temperatures. However, investigation of the effects of meat product attributes (pH, water activity, moisture, fat and muscle distribution) as well as considerations of additional variables, risks, and parameters of facility-conducted thermal processing trials is recommended to gain further insight on thermal processing behavior of both non-pathogenic E. coli inoculum and Salmonella.
Redemann, Morgan Alyse, "Evaluation of thermal process lethality in meat for non-pathogenic Escherichia coli as a surrogate for Salmonella" (2016). Open Access Theses. 889.