Influence of the incubation temperature after heat treatment upon the estimated heat resistance values of spores of Bacillus subtilis

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