MODELING THE HEAT-STRESS AND THE RECOVERY OF BACTERIAL-SPORES

After heat treatment, the temperature incubation and the medium compos ition, (pH and sodium chloride content) influence the capacity of inju red spores to repair heat damage. The concept of heat resistance D-(de cimal reduction time) and e-values (temperature increase which results in a ten fold reduction of the D value) is not sufficient and the rat io of spore recovery after incubation should be considered in calculat ions used in thermal processing of food, This paper aims to derive a m odel describing the recovery of injured sports as a function of both t he heat treatment intensity and the environmental conditions. Accordin g to data from numerous investigators, when spores are incubated in un favorable conditions, the ratio of cell recovery and the apparent D-va lue are reduced. Moreover the ratio of the apparent D-value and the es timated in optimal incubation D-value is constant and independent of t he heat treatment conditions. Beyond these observations it is shown th at the ratio of cell recovery with respect to the heat treatment F-val ue (exposure time, in minutes, at 121.1 degrees C which results in the same destruction ratio that the considered heat treatment does) is li near and can be quantified by using two factors independent of the hea t treatment: the gamma-factor reflects the degree of precariousness du e to the heat stress while the epsilon-factor reflects more intrinsica lly the incubation conditions without previous heat treatment. The gam ma-factor varies as a function of the incubation temperature according to an Arrhenius law. (C) 1997 Elsevier Science B.V.