Death rates of salmonellae in fishmeals with different water activities II.—During heat treatment

During heating of fishmeals, the death rate of salmonellae (initial count about 10 6 /g) was not constant, but decreased with time. For heat treatments at constant temperatures between 50 and 85°c, the initial death rates were the same in meals with water activity ( a w ) 0.58‐0.89, but increased with reduction of a w below 0.58. In contrast to this, the average death rate of Salmonella oranienburg , calculated after heat treatments which reduced the Salmonella count to very low or non‐detectable levels, increased strongly with a w from 0.40 to 0.80. In case of the strain S. senftenberg 775W, the relationship between a w and heat resistance was different, the maximum heat resistance being found in fishmeal at a w 0.53. The heat resistance of a strain of S. oranienburg was found to be greater than that of S. senftenberg 775W. In case of a meal with a w 0.72, infected with S. oranienburg , a heat treatment of 10 min at 80°c was found to be sufficient for reduction of the Salmonella count to non‐detectable levels. In other experiments, a much lower heat resistance was found for S. oranienburg and other salmonellae.