Effect of heat and thermosonication treatments on peroxidase inactivation kinetics in watercress ( Nasturtium officinale)

Abstract

The effect of heat and the combined heat/ultrasound (thermosonication) treatment on the inactivation kinetics of peroxidase in watercress ( Nasturtium officinale) was studied in the temperature range of 40–92.5 °C. In the heat blanching processes, the enzyme kinetics showed a first-order biphasic inactivation model. The activation energies and the rates of the reaction at a reference temperature for both the heat-labile and heat-resistant fractions were, respectively, E a1 = 421 ± 115 kJ mol −1 and E a2 = 352 ± 81 kJ mol −1, k 1 84 . 6 ° C = 18 ± 14 min - 1 and k 2 84 . 6 ° C = 0 . 24 ± 0 . 14 min - 1 . The initial relative specific activity for both isoenzyme fractions were also estimated, being C 01 = 0.5 ± 0.08 μmol min −1 mg protein −1 and C 02 = 0.5 ± 0.06 μmol min −1 mg protein −1, respectively. The application of thermosonication was studied to enable less severe thermal treatments and, therefore, improving the quality of the blanched product. In this treatment the enzyme kinetics showed a first-order model. The activation energy, the rate of reaction at a reference temperature and the initial relative specific activity were, respectively, E a3 = 496 ± 65 kJ mol −1, k 3 87 . 5 ° C = 10 ± 2 min - 1 and C 03 = 1 ± 0.05 μmol min −1 mg protein −1, proving that the enzyme became more heat labile. The present findings will help to design the blanching conditions for the production of a new and healthy frozen product, watercress ( Nasturtium officinale), with minimized colour or flavour changes along its shelf life.