Comparison of capillary and test tube procedures for analysis of thermal inactivation kinetics of mold spores

Characteristics of capillary and test tube procedures for thermal inactivat ion kinetic analysis of microbial cells were studied for mold spores. Durin g heating, capillaries were submerged in a water bath and test tubes were h eld with their caps positioned above the level of the heating medium. Therm al inactivation curves of Aspergillus niger spores in capillaries at around 60 degrees C consisted of a shoulder and a fast linear decline, whereas cu rves in test tubes consisted of a shoulder, a fast linear decline, and a ho rizontal tail. There were no significant differences in values of the rate and the delay of fast declines in curves between the procedures. Some exper iments were done to clarify the cause for tailing with test tubes. There we re no tails with test tubes whose inner walls were not contaminated by A. n iger spores, suggesting that tails arise from A. niger spores contaminating the inner walls of test tubes. Temperature of the inner wall at the level of a heating medium was lower than that of the medium. Further, there were no tails for test tubes submerged in the heating medium. These results show ed that the reason for survival of contaminants on the upper wall of test t ubes was that cells were not subjected to sufficient inactivation temperatu re. Finally, thermal inactivation curves of A. niger spores in capillaries at various constant temperatures were studied. Curves consisted of a should er and a fast linear decline at 57 degrees C and above, whereas curves at b elow 57 degrees C consisted of a shoulder, a fast linear decline, and a slo ping tail.