Purpose: This study was conducted to determine the effect of pH, moisture, and salt in combination with extended cook and cool on the growth/survival of pathogens in cured ham.
Methods: Ten cured ham (156 mg/kg NaNO2) treatments were formulated to represent ranges of 55 to 75% moisture, pH 5.8 to 6.4, and 1.5 to 3.0% salt using a full factorial design. Raw treatments were inoculated with three log CFU/g Listeria monocytogenes, Staphylococcus aureus, Salmonella spp., or Clostridium perfringens spores and vacuum packaged (25 g/package). Samples were heated (linear increase from 10 to 54°C) according to Appendix A (in 6 hours) or slow-cook (in 10 hours), and then continued heating to an internal temperature of 70°C. Samples were slow cooled from 54 to 4°C in 25 hours (extended from Appendix B). Duplicate samples per treatment were assayed at zero-time and at internal temperatures 32, 54, 70, 29, and 4°C by enumerating on appropriate selective agars.
Results: All treatments inoculated with L. monocytogenes, S. aureus, Salmonella spp., or C. perfringens inhibited growth during control and slow cook. All three vegetative pathogens were inactivated by cooking to 70°C. No difference in survival was observed between Appendix A and slow-cook treatments. In contrast, C. perfringens increased 4.7, 3.0, and 1.7 log during the 25-h extended cooling in 75% moisture treatments with pH 6.4/1.5% NaCl, pH 6.4/3.0% NaCl, and pH 5.8/1.5% NaCl, respectively. In addition, 55% moisture ham with pH 6.4 and 6.1 and low salt supported a >1.5 log increase. None of the other treatments supported growth during the 25-h extended cool.
Significance: This study confirmed the critical nature of salt, pH, and moisture for pathogen inhibition in cured meat during extended dwell times.