Thermal inactivation of lipoxygenase and hydroperoxytrienoic acid lyase in tomatoes

Lipoxygenase (LOX) and hydroperoxytrienoic acid lyase (HPL) activities were determined in tomato juice from four cultivars of processing tomatoes. Large differences in total activity levels were found between different cultivars. Thermal inactivation kinetics of these two enzymes were determined for two cultivars used in cold break processing. LOX inactivation did not follow simple first order kinetics. The data could be fitted by assuming that three isoforms of LOX are present. HPL inactivation also indicated the presence of labile and resistant forms with the resistant form showing simple first order inactivation kinetics. The inactivation kinetics for both enzymes indicate that they would be rapidly inactivated at the cold break target temperature of 60 °C. It is questionable whether the activity of these two enzymes contributes to the superior flavour associated with products produced by the cold break process.