The effect of growth temperature, process temperature, and sodium chloride on the high-pressure inactivation of Listeria monocytogenes on ham

This study investigated the effect of growth temperature (8-32 A degrees C), process temperature (-17 to 32 A degrees C), and sodium chloride concentration (0-3 %) on the lethality of pressure to Listeria monocytogenes. Pressure treatments were performed using a 5-strain cocktail of L. monocytogenes. Cultures grown at 8 A degrees C were more resistant to pressure than cultures grown at 20 or 32 A degrees C. Pressure treatments of the Listeria cocktail indicated that Listeria were most resistant to pressure at -5 or +5 A degrees C. The effect of pressure was further evaluated at 500 MPa and +5 A degrees C in buffer containing 1 or 3 % NaCl. Cultures treated in the presence of 3 % NaCl were more resistant than cultures treated in the presence of 1 % NaCl. Results obtained in buffer were compared to treatment of cooked ham containing 1 or 3 % NaCl. L. monocytogenes was more resistant in ham with 3 % NaCl when compared to ham with 1 % NaCl. L. monocytogenes grown at 32 A degrees C were slightly more resistant to pressure when compared to cultures grown at 8 A degrees C. Refrigerated storage of treated samples for 4 weeks demonstrated that L. monocytogenes recovered from all treatments with a pressure-holding time of 8 min or less. In conclusion, the effect of high-pressure processing strongly depends on growth temperature, process temperature, and the food matrix. To generally achieve a 5-log reduction of L. monocytogenes on ready-to-eat meats, combinations of pressure with elevated temperature or other antimicrobial hurdles are necessary.