Inactivation kinetics of Bacillus spores in batch- and continuous-heating systems

Kinetic parameters for the thermal inactivation of Geobacillus stearothermophilus ATCC 7953 and Bacillus flexus 1316 spores were determined for temperatures ranging from 100 to 130 °C and 100 to 125 °C, respectively. Ringer's solution (pH = 7.1) was used as the heating medium. A batch-heating system, in which the samples are kept in small tubes that are heated with steam, and a continuous-heating system, which is based upon a heat exchanger and enables high temperature short time heating, were used. Experiments were conducted in both systems and the heat resistances of the two species were determined. Additionally, a comparison of the two heating systems was carried out. The reaction rate constant at the reference temperature, kref, the activation energy, Ea, the D-value and the z-value were calculated for the two species. The D-values at 121 °C for G. stearothermophilus and for B. flexus in the batch-heating system were found to be 42 and 4.2 s, respectively. The z-values were calculated as 13 K for G. stearothermophilus and 16 K for B. flexus in the batch-heating system. The results from both systems differed significantly, wherein the continuous-heating system had been more lethal than the batch-heating system.