INFLUENCE OF THE INCUBATION-TEMPERATURE AFTER HEAT-TREATMENT UPON THEESTIMATED HEAT-RESISTANCE VALUES OF SPORES OF BACILLUS-SUBTILIS

The influence of the incubation temperature on the estimated heat resi stance for survivors after heat treatment was investigated. The surviv al curves and the D-t values of spores of Bacillus subtilis heated at different temperatures in pH 7 buffer, obtained after incubating survi vors at different temperatures (30 degrees, 37 degrees, 44 degrees or 51 degrees C), were compared. The incubation temperature influenced th e profile of survival curves. Lower incubation temperatures led to big ger D-t values and longer shoulders. D-t values obtained after incubat ing at 30 degrees C were higher (x3 approx.) than those obtained by in cubating at 51 degrees C. The incubation temperature did not modify z values (z = 9.1). These results show that shoulders are not only due t o the activation of dormant spores but also to heat damage repair mech anisms. From the profile of survival curves at different incubation te mperatures it would seem that heat damage is accumulative. Cells can r epair the initial heat injury, but the accumulation of injuries would eventually make the damage irreversible.