Refined approach to the evaluation of heat resistance applied to Enterobacteriaceae in cheese stretching

Heat resistance of bacteria is a factor potentially limiting the production of safety foods. We focused on five Enterobacteriaceae strains related to cheese stretching and sub-pasteurisation experimental temperatures of 50-59 °C. Heat resistance was screened and obtained data were fitted to a classical log-linear model with D-values indicating highly heat-resistant strains used. For example in Klebsiella oxytoca S525, D(50)-value was 96.1 min and D(59)-value 5.1 min. In subsequent detailed measurements, the shape of inactivation curves was sigmoid with defined lag, log-linear and stationary phase. We suggest calculating refined D-values (Dr-values) using only data obtained in log-linear phases, namely Dr(temperature; lag phase). In K. oxytoca S525, the obtained results were: Dr(50; 80.9) = 61.7 min, Dr(53; 12.4) = 36.8 min, Dr(56; < 10) = 10.6 min, and Dr(59; < 3) = 4.3 min. The research of particular inactivation phases can provide interesting findings both in science and industrial practice, especially concerning the passage or persistence of hazardous strains in food processing plants.