Inactivation of Listeria monocytogenes and Salmonella spp. during cooking of country ham and fate of L. monocytogenes and Staphylococcus aureus during storage of country ham slices

Authors: Luchansky, John; BARLOW, K - Hawkins, Inc; WEBB, B - Hawkins, Inc; BECZKIEWICZ, A - Hawkins, Inc; MERRILL, B - Hawkins, Inc; VINYARD, B - Hawkins, Inc; Shane, Laura; Shoyer, Brad; Osorio, Manuela; CAMPANO, STEPHEN - Hawkins, Inc; Porto-Fett, Anna

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2024
Publication Date: 1/12/2024
Citation: Luchansky, J.B., Barlow, K., Webb, B., Beczkiewicz, A., Merrill, B., Vinyard, B.T., Shane, L.E., Shoyer, B.A., Osoria, M., Campano, S.G., Porto Fett, A.C. 2024. Inactivation of Listeria monocytogenes and Salmonella spp. during cooking of country ham and fate of L. monocytogenes and Staphylococcus aureus during storage of country ham slices. Journal of Food Protection. https://doi.org/10.1016/j.jfp.2024.100222.
DOI: https://doi.org/10.1016/j.jfp.2024.100222

Interpretive Summary: For over 400 years country hams have been widely enjoyed in the U.S. as an entrée or side dish, biscuit meat, and/or ingredient of soups and stews. Country hams are both safe and wholesome due to an internal salt content of greater than 4.0% and a final weight that is less than 18% of the fresh/uncured weight of a raw ham. Country hams are not required to be labeled as ready-to-eat (RTE) because the intended use can be RTE or not RTE. Despite a comparatively low public health risk due to its intrinsic properties, on rare occasion there have been both product recalls and human illnesses associated with country hams. Thus, we evaluated the effectiveness of select time/temperature parameters listed in the USDA FSIS Cooking Guideline for Meat and Poultry Products (aka “Appendix A”) to eliminate cells of Listeria monocytogenes and Salmonella spp. inoculated (within our laboratory) onto the surface of country hams at levels of 1 billion cells per ham. In brief, after overnight storage at 4°C to allow for cells to attach to the meat, vacuum-packaged, inoculated country hams were cooked to an internal temperature of 130°F (54.4°C) instantaneous, 145°F (62.8°C) and held for 4 min, 153°F (67.2°C) and held for 34 seconds, or 160°F (71.1°C) instantaneous in a circulating water bath maintained at 168.8°F (76°C). These time/temperature combinations reduced levels of L. monocytogenes and Salmonella spp. on country hams by about 16 million cells per ham. Given its extended shelf-life and potential for contact with undesirable bacteria during processing or packaging, we also monitored the fate of cells of Listeria monocytogenes and Salmonella spp. inoculated onto slices of country hams during extended storage at room temperature, that being about 20°C. The results confirmed that country hams did not support growth of either of these pathogens during extended storage at room temperature. Our findings will help regulators develop policies, measure health risks and provide information to processors and consumers.

Technical Abstract: Viability of cells of Listeria monocytogenes, Salmonella spp., or Staphylococcus aureus was quantified following cooking or storage of country hams. Hams (average = ca. 3.4 ± 0.5 kg each; average = ca. =18% shrinkage) were used as provided by the processor (i.e., “salted hams”), or desalted in tap water (i.e., “desalted hams”), or dried for an additional period (i.e., “extra dried hams”). For thermal inactivation studies, country hams were surface inoculated (ca. 9.5 log CFU/ham) with a rifampicin-resistant, multi-strain cocktail of L. monocytogenes or Salmonella spp. and cooked in a bag to an internal temperature of 130°F (54.4°C) instantaneous, 145°F (62.8°C) and held for 4 min, 153°F (67.2°C) and held for 34 seconds, or 160°F (71.1°C) instantaneous in a circulating water bath. Results showed that regardless of ham type, the time/temperature combinations tested herein were sufficient to deliver a 6.7 to =7.2 log reduction of cells of L. monocytogenes or Salmonella spp. Differences in product pH, moisture content, and aw did not have an appreciable impact on thermal inactivation of cells of L. monocytogenes or Salmonella spp. on country hams. For shelf-life studies, slices of “salted” country hams were surface inoculated (ca. 5.5 log CFU/slice) with rifampicin-resistant cells of a multi-strain cocktail of L. monocytogenes or S. aureus and then stored at 20°C. Levels of S. aureus increased by ca. 1.4 log CFU/slice during storage for 90 days whereas levels of L. monocytogenes remained relatively unchanged (= 0.15 log increase). Our data validated that cooking parameters elaborated in the USDA FSIS Guidelines for Meat and Poultry Products (Revised Appendix A) are sufficient to deliver significant reductions (ca. =7.2 log CFU/ham) in levels of L. monocytogenes and Salmonella spp. In addition, in the event of postprocessing contamination, country ham does not support appreciable outgrowth (<1.4 log CFU/slice increase) of L. monocytogenes or S. aureus.