SummaryContinuous flow-type reactors have been used to study the kinetics of biological systems for quite some time. For continuous media sterilization, tubular flow reactors are particularly useful being simple in character and easy to control. However, one aspect quite often neglected in sterilization calculations is the residence time distribution of the reactor system. Serious errors in estimating the degree of bacterial destruction can be encountered if the residence time distribution is neglected; especially when a high degree of destruction is desired. This paper reports a study made to characterize and use the residence time distribution of a tubular reactor in the interpretation of high-temperature, short exposure time data for inactivation of Bacillus steurothemzophilus spores. Mathematical models accounting for the residence time distribution of the tubular reactor have been proposed and employed to obtain high-temperature death-rate data.
The kinetics of death of
Bacillus stearothermophilus
spores (FS 7954) suspended in phosphate buffer (pH 7) were studied over a temperature range of 127.2 to 143.8 C and exposure times of 0.203 to 4.150 sec. These short exposure were achieved by use of a tubular flow reactor in which a suspension of spores was injected into a hot flowing stream at the entrance of the reactor. Thermal equilibria of the suspension with the hot stream was achieved within 0.0006 sec. After flow through a fixed length of reactor, the stream containing the spores was cooled by flash vaporization and then assayed for viable count. The death rate data were fitted by a logarithmic expression. However, logarithmic death rate was only approximated in the tail or high-kill regions of exposure. Death rate constants obtained from this portion of the data were found to correlate by Arrhenius as well as Absolute Reaction Rate Theory relationships. Thermal-death time curves were found to correlate the data rather poorly. The activation energy and frequency constant for an Arrhenius relationship fit of the data were found to be 83.6 kcal/gmole and 10
47.2
min
-1
, respectively. The standard enthalpy and entropy changes for an Absolute Reaction Rate Theory relationship fit of the data were found to be 84.4 kcal/gmole and 157 cal/gmole-K, respectively.
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