Kinetics of thermal inactivation of tomato lipoxygenase

The kinetics of thermal inactivation of tomato lipoxygenase were studied. Tomato dices and a non-purified enzymatic extract were treated at different time–temperature combinations in the range of 0–150 min and 80–98 °C and the thermodynamic (activation energy) and kinetic (DT and z) parameters for lipoxygenase inactivation were calculated. The kinetic behaviour of lipoxygenase from the tomato samples indicated the presence of two different isoenzymes having different thermal stabilities. Furthermore, the results showed that the isoenzymes were more heat-resistant than expected on the basis of literature reports and that the determined DT and z values for lipoxygenase were orders-of-magnitude larger than those for microrganisms. This suggested that high temperature-short time treatments cannot be sufficient to achieve complete inactivation of tomato lipoxygenase.