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ARS Home » Northeast Area » Wyndmoor, Pennsylvania » Eastern Regional Research Center » Characterization and Interventions for Foodborne Pathogens » Research » Research Project #439564

Research Project: Incidence of Bacterial Pathogens in Regulated Foods and Applied Processing Technologies for Their Destruction

Location: Characterization and Interventions for Foodborne Pathogens

2023 Annual Report

Objective 1: Determine the recovery rate, population levels, relatedness, persistence, and harborage sites of target pathogens in raw, further processed, and/or ready-to-eat foods from production through to consumption to assist in risk assessments and communication. [C1, PS1] Sub-Objective 1.A: Determine the prevalence and levels of Lm, STEC, and Salmonella in RTE foods at retail, raw organ meats from abattoirs, and frozen bakery products containing meat and vegetables from food retailers. Sub-Objective 1.B: Determine the relatedness of Lm, STEC, and Salmonella recovered from foods using molecular typing methods such as PFGE and WGS. Sub-Objective 1.C: Assess perceptions, food safety attitudes, and self-reported behaviors related to observed food safety hazards by consumers who shop at grocery stores. Objective 2: Validate lethality (heating) and stabilization (cooling) processes for ready-to-eat (RTE) and not ready-to-eat (NRTE) meat and poultry products. [C1, PS5] Sub-objective 2.A: Validate lethality and stabilization processes to control of Salmonella, Lm, and Cperf in non-intact and specialty/ethnic pork and beef products. Sub-objective 2.B: Validate consumer-relevant cooking times, temperatures, and appliances to control target pathogens in (multi-species) bakery products containing meat and vegetables. Sub-objective 2.C: Validation of cooking and cooling profiles for large mass meat products to achieve stabilization performance standards that prevent growth of Cperf. Objective 3: Develop, optimize, and validate biological, physical, and chemical interventions and processes to control target pathogens in raw, RTE, and specialty/ethnic foods. [C1, PS5] Sub-objective 3.A: Apply interventions to control target pathogens in RTE meats and multi-component meat-based salads and salsas. Sub-objective 3.B: Validate food-relevant interventions to control target pathogens in plant-sourced meat alternatives. Sub-objective 3.C: Evaluation of the impact of processing parameters of dry-cured fermented meat on lethality towards STEC, Salmonella, and Lm. Sub-objective 3.D: Develop and/or validate strategies to control pathogens in forcemeats.

The overarching theme of this research plan is to identify where pathogens enter the food supply, where, how, and why they persist in foods, and/or what can be done to reduce their levels or to eliminate them along the farm to fork continuum. Target pathogens will include Listeria monocytogenes (Lm), Salmonella, Clostridium perfringens (Cperf), and Shiga toxin-producing cells of Escherichia coli (STEC). Target foods will include raw and ready-to-eat meats, dairy, baked foods, and vegetables, as well as simulated meats and specialty/ethnic foods, targeted for human and animal consumption. A primary focus will be to identify entry points, sources, and levels of target pathogens in foods or within food processing, food service, and retail environments, and to elucidate factors contributing to their survival and persistence. Phenotypic and molecular methods, including pulsed-field gel electrophoresis (PFGE) and whole genome sequencing (WGS), will be used to identify and differentiate isolates from the farm through distribution and at retail to determine pathogen relatedness, niche, persistence, and succession. Another focus will be to validate processes and interventions such as fermentation, drying, high pressure, biopreservatives, food grade chemicals, and heat (e.g., grilling and sous vide), alone or in combination, to inhibit/remove undesirable bacteria and better manage pathogen presence, populations, and/or survival during manufacture and/or subsequent storage of target foods. We will also develop and optimize methods to deliver antimicrobials to food systems, including electrostatic spraying and various strategies to introduce interventions into/onto foods or food containers/packaging (e.g., SLIC®). Our findings will assist numerous producers and processors with meeting current regulatory guidelines and assist regulators such as the DHHS FDA and the USDA FSIS with making science-based policy decisions, thereby enhancing the safety of the Nation’s food supply.

Progress Report
Progress was made on the execution of our programmatic goals to recover, characterize, and control target pathogens in raw, further processed, and ready-to-eat (RTE) foods. These efforts were assisted and expanded via our longstanding partnerships with food safety professionals in government, industry, and academia related to validation of processes and chronicling pathogen presence and fate from production through to consumption of food. Target pathogens included Salmonella (Sal), Shiga toxin-producing Escherichia coli (STEC), and Listeria monocytogenes (Lm), whereas target foods included country hams, bakery products with meat filling, fermented meats, and dry-cured hams. As one example, we evaluated clean label ingredients (i.e., buffered vinegar) to control outgrowth of Sal in raw chicken tenders during shelf life. Results to date validated buffered vinegar as an alternative to “lactates” as an ingredient for controlling the outgrowth of Sal onto surface of raw chicken tender during refrigerated shelf life. Other examples include confirmation of the antilisterial potential of organic acid as ingredients (i.e., lactates, acetate, and diacetate) for RTE bratwurst and RTE chicken strips specifically formulated by an industry partner. Results confirmed that, in the event of post process contamination, inclusion of selected organic acids, alone or in combination, into RTE meats as ingredients would preclude outgrowth of Lm during extended refrigerated storage. Regarding fermented meats, we validated the effect of post-fermentation heating parameters to deliver greater than 100,000 cells reduction of Sal in Genoa salami. These data ensured the safety of these products/processes, while saving processing times/monies, and without adversely affecting product quality. We also confirmed that cooking country hams at time:temperature parameters prescribed in Appendix A delivered the requisite reductions of surface-inoculated cells of Sal and Lm when cooked in vacuum-sealed bags in a temperature-controlled water bath. In collaboration with a regulatory partner, we also established that cooking bakery products comprised of beef or poultry (i.e., pot pies) in a convection oven at cooking conditions prescribed in Appendix A was sufficient to deliver reductions of 100,000 to 3 million cells of Sal. Lastly, prefatory studies established that casing permeability did not appreciably alter the observed lethality of Sal during fermentation: reductions of about 1 million cells were observed for batter stuffed into either a 32-mm hog casing (semi-permeable) or a 35-mm cellulose casing (impermeable). Collectively, our data are used by industry to validate their processes and by regulators to make science-based policy decisions. Our unique ability to work with real pathogens and pilot-scale equipment allows for the ensuing ground-truthed results to be used directly by our various partners.

1. Thermal inactivation of Salmonella in turkey burgers. Cooking is the most effective consumer practice to eliminate pathogens found in raw meat and poultry products. The USDA FSIS requires poultry burgers to be cooked to an instantaneous internal temperature of at least 165degF to eliminate the relatively low levels of pathogens that on occasion may be present. However, over the past decade there have been several recalls and illnesses attributed to consumption of undercooked and/or improperly handled ground poultry due to contamination with cells of Salmonella (Sal). Therefore, ARS scientists in Wyndmoor, Pennsylvania, in collaboration with university cooperators, conducted research to quantify inactivation of Sal in turkey burgers of different thicknesses, previously stored refrigerated or frozen, following pan frying in different volumes of cooking oil. Ground turkey was inoculated with Sal (ca. 3.2 million cells per g), formed into about 1.25 or 2.5 cm thick burgers, stored at 4degC (18 h) or at -20degC (30 days), and then cooked to temperatures ranging from 57.6 to 82.2degC in a saute pan with 15 or 30 mL of canola oil. Results showed that regardless of oil volume, cooking refrigerated or frozen 1.25 or 2.5 cm thick burgers to internal temperatures of 57.2, 65.6, 73.9, or 82.2degC delivered reductions of about 650 to greater than 1 million cells of Sal per gram. Our findings validate that cooking to the USDA FSIS recommended internal temperature of 165degF eliminated about 125,000 to 1.25 million cells per gram of Sal in refrigerated or frozen ground turkey patties cooked on a frying pan.

2. Fate of pathogens on slices of beef salume during storage. There has been considerable interest in utilizing beef as the sole protein source in various specialty/ethnic meats that are traditionally made exclusively with pork, including dry-cured fermented salume. Although fermentation and drying are sufficient to both ensure safety and achieve shelf stability of fermented meats, on occasion pathogens such as Listeria monocytogenes (Lm), Salmonella (Sal), and Shiga toxin-producing Escherichia coli (STEC) have been recovered from these products. Also, a handful of recalls and outbreaks have been linked to consumption of fermented salume, including soppressata, when contaminated with these pathogens. Therefore, ARS scientists in Wyndmoor, Pennsylvania, conducted research to determine if an all-beef soppressata would allow for survival or support outgrowth of these pathogens during storage. Cells of Lm, Sal, or STEC were inoculated onto slices (about 10,000 cells per slice) of an all-beef soppressata and viability was monitored during extended storage. Storage of vacuum-sealed slices of soppressata at refrigeration (4degC) or at room (20degC) temperatures for 90 days resulted in reductions of all three pathogens by about 160 to greater than 2,000 cells per slice. In summary, slices of the commercial-produced soppressata selected for this study did not provide a favorable environment for either survival or outgrowth of surface-inoculated cells of Lm, Sal, or STEC during storage. Our validation of the wholesomeness of (slices of) an all-beef soppressata confirms the safety and broadens the market for this category of dry-cured, Italian-type salume.

3. Inactivation of pathogens on country hams. Meat processors rely on time/temperature parameters prescribed in USDA FSIS Appendix A guidelines to scientifically affirm that cooking/processing parameters for a specific product are sufficient to achieve the requisite reductions of regulated pathogens, such as Listeria monocytogenes (Lm) and Salmonella (Sal). However, USDA FSIS guidelines as elaborated in Appendix A were not originally intended for products of lower water activity that are dried and then cooked, such as country hams. Thus, ARS scientists in Wyndmoor, Pennsylvania, in collaboration with USDA FSIS scientists, conducted research to validate that cooking processes in Appendix A are sufficient to eliminate pathogens Lm and Sal during cooking. Country hams were surface inoculated with about 3 billion cells of Lm or Sal per ham, vacuum sealed in a plastic bag, and then cooked to an internal temperature of 130degF instantaneous, or 145degF and held for 4 min, or 153degF and held for 34 seconds, or 160degF instantaneous stipulated in a circulating water bath maintained at 168.8degF. Results validated that cooking parameters elaborated in Appendix A are sufficient to deliver significant reductions (about 15 million cells per ham) in levels of Lm and Sal. These data will facilitate risk analysis and policy development essential for lowering the likelihood of future recalls and illnesses associated with country hams.

4. Thermal inactivation of Salmonella in pot pies containing meat. Salmonella (Sal) may contaminate both the raw ingredients used for the filling or dough components of meat pies and has been associated with the finished product. Thermal processes commonly used for bakery products containing meat may not meet recommended lethality performance guidelines required by USDA FSIS. Hence, ARS scientists in Wyndmoor, Pennsylvania, in collaboration with USDA FSIS scientists, conducted research to evaluate the efficacy of time/temperature parameters elaborated in Appendix A for thermal inactivation of Sal within beef or poultry pot pies prepared with and without gravy. Pot pies prepared with ground beef or poultry, and with or without gravy, were inoculated with 10 to 100 million cells of Sal and then stored at -20degC for 48 hours. Frozen (inoculated) pot pies were cooked to an internal temperature of 136degF instantaneous, 145degF and held for 4 min, 153degF and held for 34 seconds, 160degF instantaneous, or 165deg F instantaneous in an electric convection oven. Results validated that the above-mentioned time/temperature parameters as elaborated in the Appendix A guidelines were sufficient to achieve reductions of greater than 3.2 million cells of Sal in all types of pot pies tested. These scientifically-sound data on thermal inactivation of Sal in pot pies will populate data voids for risk analyses and risk assessment, provide the scientific basis for pending or future policy development, and appreciably lower any risk to public health on the rare occasion of product contamination.

Review Publications
Luchansky, J.B., Campano, S., Rieker, M., Mahoney, C., Vinyard, B.T., Shane, L.E., Shoyer, B.A., Osoria, M., Porto Fett, A.C. 2022. Viability of listeria monocytogenes and salmonella spp. on slices of a german-style bologna containing blends of organic acid salts during storage at 4 or 12C. Journal of Food Protection. 86(1):100019.
Luchansky, J.B., Shane, L.E., Osoria, M., Vinyard, B.T., Shoyer, B.A., Campano, S.G., Porto Fett, A.C. 2023. Fate of Listeria monocytogenes, Salmonella spp., and Shiga toxin-producing Escherichia coli on slices of an all-beef soppressata during storage. Foods.
Porto Fett, A.C., Mccoy, A., Shane, L.E., Henry, E., Osoria, M., Shoyer, B.A., Campano, S.G., Burson, D.R., Luchansky, J.B. 2022. Fate of Listeria monocytogenes and shiga toxin-producing Escherichia coli on bresaola slices during storage. Meat and Muscle Biology. 6(1).