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

摘要

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℃. 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 kJmol~(-1) and E_(a2) = 352 ± 81 kJmol~(-1), k_1_(84.6℃) = 18 ± 14min~(-1) and k_2_(84.6℃) = 0.24 ± 0.14mm~(-1). The initial relative specific activity for both isoenzyme fractions were also estimated, being C_(01) = 0.5 ± 0.08 μmolmin~(-1) mg protein~(-1) and C_(02) = 0.5 ± 0.06 μmolmin~(-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℃) = 10 ± 2min~(-1) and C_(03) = 1 ± 0.05 μmolmin~(-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.