Determination of an Effective Treatment Temperature of Chemical and Biological Reactions

Thermal microbial inactivation kinetics can be influenced significantly by the non-isothermal condition of the sample tested. In many instances, it is practically difficult to maintain the temperature constant during chemical and biological reactions. To minimise error caused by such non-isothermal condition, an effective treatment temperature was derived based on fundamental principles of reaction kinetics. This effective temperature was significantly different from the arithmetic mean temperature due to the exponential effect of temperature on reaction rate. In order to validate the developed concept, Escherichia coli ATCC 25922 suspended in simulated milk ultra filtrate was thermally inactivated using test tubes of different diameters. As expected, the D value was accurately related to the water bath temperature only when small capillary tube was used for the measurements. As the tube diameter increased, the D value increased and was found not to be related to the water bath temperature. On the other hand, the measured D values using different tube diameters correlated very well with the calculated effective treatment temperature. Our calculations show that the effective temperature can be calculated with reasonable degree of accuracy even if there is some uncertainty in the value of the activation energy of the reaction. A number of important applications are addressed in this paper to show the importance of using such a concept. The use of effective temperature will allow accurate comparison of reaction kinetics reported in the literatures on chemical and biological reactions.