Thermal Inactivation of Pectin Methylesterase, Polygalacturonase, and Peroxidase in Tomato Juice

Thermal inactivation kinetics have been determined for pectin methylesterase (PME), polygalacturonase (PG), and peroxidase (POD) in tomato juice. Two parameters, the inactivation rate constant (k) at a reference temperature and the activation energy for inactivation (E(a)), were determined for each enzyme. For PME and PG, the k and E(a) values reported here do not agree with those in several previously published reports. These differences can be explained either by the differences in pH values used for inactivation determinations or by inadequacies in the heating methods used in some previous studies. POD showed simple first-order inactivation kinetics and was less thermally stable than either PME or PG. When different cultivars of tomatoes were evaluated, there was no difference in the thermal inactivation kinetics of these enzymes.