A VITALISTIC MODEL TO DESCRIBE THE THERMAL INACTIVATION OF LISTERIA-MONOCYTOGENES

Thermal inactivation of microorganisms has traditionally been describe d as log-linear in nature, that is the reduction in log numbers of sur vivors decreases in a linear manner with time. This is despite a pleth ora of data that shows consistent deviations from such kinetics for a wide range of organisms and conditions and that cannot be accounted fo r by experimental artifacts. Existing thermal death models fail to tak e such deviations into account and also fail to quantify the effects o f heating menstruum on heat sensitivity. The thermal inactivation of L isteria monocytogenes ATCC 19115 has been investigated using a factori ally-designed experiment comparing 45 conditions of salt concentration , pH value and temperature. Heating was carried out using a Submerged Coil heating apparatus that minimized experimental artifacts. Low pH v alues increased, whilst high salt concentrations decreased heat sensit ivity. Results showed a significant and consistent deviation from log- linear kinetics, particularly at low temperatures. A number of distrib utions were tested for suitability to describe the variability of heat sensitivity within the population of heated cells (vitalistic approac h). The use of the logistic function and log dose (log time) allowed t he development of an accurate unifying predictive model across the who le range of heating conditions. It is proposed that this approach shou ld be tested as a generalized modeling technique for death kinetics of vegetative bacteria.