Thermal resistance of salmonellae isolated from dry milk

Abstract

Salmonella anatum, S. binza, S. cubana, S. meleagridis, S. newbrunswick, and S. tennessee isolated from dry milk, and S. senftenberg 775W were studied for heat resistance to determine whether these organisms would survive pasteurization as recommended by the 1965 Pasteurized Milk Ordinance of the U.S. Public Health Service. Thermal inactivation determinations were made on washed cells of the test microorganisms suspended in sterile whole milk. Excluding S. senftenberg, D values ranged from 3.6 to 5.7 sec at 62.8 C, from 1.1 to 1.8 sec at 65.6 C, and from 0.28 to 0.52 sec at 68.3 C. Corresponding values for S. senftenberg were 34.0, 10.0, 1.2, and 0.55 sec for respective exposure temperatures of 65.5, 68.3, 71.7, and 73.9 C. The present milk pasteurization processes as recommended by the Public Health Service will inactivate all seven strains of salmonellae studied, provided that the initial concentration does not exceed a calculated 3 x 10(12) salmonellae per ml of milk.