Fate of Selected Pathogens in Vacuum-Packaged Dry-Cured (Country-Style) Ham Slices Stored at 2 and 25°C†

Abstract

Whole dry-cured (country-style) hams from six manufacturers were sliced and the slices randomly allotted into five treatment groups per manufacturer. One treatment group served as a control and slices in the four other treatment groups were inoculated with approximately 105 CFU/g of ham of either Escherichia coli O157:H7, Listeria monocytogenes, a mixture of three Salmonella spp. (Salmonella typhimurium, Salmonella enteritidis and Salmonella choleraesuis), or Staphylococcus aureus. All ham slices were vacuum-packaged with half of the packages in each treatment group stored at 25°C and half stored at 2°C. Two packages from each manufacturer for each treatment and storage temperature were examined after storage for 0,7, 14,21, and 28 days. S. aureus was detected in 2 of 60 control slices, Salmonella in 2 of 120, L. monocytogenes in 4 of 120, and E. coli O157:H7 was not detected in any of the 120 control ham slices analyzed before or after storage. Aerobic (26 and 35°C) populations of the control vacuum-packaged hams slices increased (P < 0.05) with storage time and the increase in populations was greater (P < 0.05) in vacuum-packaged hams slices at 25 than at 2°C. The extent of the decreases in populations of the inoculated pathogens during storage of vacuum-packaged dry-cured ham slices varied with manufacturer (P < 0.05) and storage temperature (P < 0.05). Decreases in Salmonella spp. and E. coli O157:H7 populations were greater (P < 0.05) in slices stored at 25 than at 2°C, while decreases in L. monocytogenes were similar at both storage temperatures. Staphylococcus aureus enterotoxin was not detected in either S. aureus-inoculated or control ham slices after storage for 28 days. Survival of these pathogens in vacuum-packaged dry-cured ham slices suggests that contaminated hams may pose a safety risk to consumers if consumed without adequate cooking.