The impact of hot and cold processing on the survival and/or growth of Salmonella, Listeria monocytogenes, pathogenic Yersinia enterocolitica, Aeromonas hydrophila, and Campylobacter spp. On inoculated pork loins was studied. Loin pieces were inoculated with pathogen-containing feces, then vacuum packaged directly after hot boning (hot packaging), vacuum packaged after chilling for 1 d, or left unpackaged. Pathogen numbers were assayed after storage at 1 + 1°C for 0, 1, 2, 5, and 9 d. Campylobacter numbers decreased during the storage period, but the organisms could still be recovered after 9 d storage. A lower Campylobacter survival rate was observed on unpackaged pork loin pieces. The other pathogens were less affected by packaging treatment. Numbers of L. monocytogenes increased by approximately 1-log10 CFU/cm2. Survival and growth of A. hydrophila during refrigerated storage varied between trials. In Experiment 1, numbers increased by ca. 2-log10 CFU/cm2, while levels were stable or decreased slightly in Experiment 2. Salmonella levels decreased during storage, with the greatest survival observed on hot-packaged pork. Despite the fact that pork loins were inoculated with ca. 102 CFU pathogenic Y. enterocolitica per cm2, the organism was recovered only sporadically during the storage period. This may be due to competition with the natural microflora. Existing procedures are often inadequate for recovering small numbers of pathogenic Y. enterocolitica in the presence of large numbers of competing flora. Until recovery procedures are improved, the effect of packaging treatment on pathogenic Y. enterocolitica cannot be determined.
1Meat Science Research Laboratory, U.S. Dept. of Agriculture, Agricultural Research Service, PQD1, Bldg 201, Barc-East, Beltsville, MD 20705-2350.
2Microbiology Division, Food Safety & Inspection Service, U.S. Dept. of Agriculture, Beltsville, MD.
3Dept. of Microbiology, Biological Laboratory, Vrije Universiteit, Amsterdam, The Netherlands.