Thermal resistance of salmonellae and staphylococci in foods.

The heat-resistant Salmonella senftenberg 775W and two strains of Staphylococcus aureus were tested at temperatures up to 68.3 C (71.1 C for S. senftenberg) in four different media. From the survival data, decimal reduction times (D values) were calculated for each set of conditions, and decimal reduction time curves were constructed for each bacterial strain in each medium. Slopes of decimal reduction time curves (Z(D)) ranged from 4.52 to 6.38 C with a single exception. There was no statistical heterogeneity among the remaining values. Results were in close agreement with published results of similar studies conducted at somewhat lower temperatures and support the practice of using a slope value (Z(D)) of 5.56 C for establishing time-temperature relationships for food processing. It is recommended that such a decimal reduction time curve not be extrapolated to temperatures more than 5.56 C higher than those actually tested.