EFFECT OF HEATING RATE ON THE THERMAL INACTIVATION OF LISTERIA-MONOCYTOGENES

In order to quantify the effect of heating rate on the thermal inactiv ation of Listeria monocytogenes an accurate means of describing the in activation kinetics at near instantaneous heating was used. Survivor c urves for L. monocytogenes, at near instantaneous heating, were obtain ed over the temperature range 50-64 degrees C. The use of a linear fun ction to describe the data would have given only a poor approximation of the true inactivation kinetics. With a model based on a logistic al gorithm extremely accurate descriptions were made. In processes which had rates of heating less than or equal to 5.0 degrees C min(-1), sign ificant deviations of real kill from predicted kill were observed. Pre dicted kill assumed that heating rate did not affect the inactivation kinetics of a thermal process. At rates of heating between 5.0 and 0.7 degrees C min(-1) the deviation greatly increased as the rate of heat ing decreased; approximately a 1.7 x 10(5)-fold difference at 0.7 degr ees C min(-1). Maximum thermotolerance was induced at rates of heating less than or equal to 0.7 degrees C min(-1). The increased thermotole rance during slow rates of heating was analogous to the induction of t he heat-shock response. The models described in this work allow for co nfident assessments of safety to be made not only at near instantaneou s heating but also when the heating rate varies.