Thermal Inactivation and Kinetic Characterisation of Peroxidase from Leaves of Brassica chinensis L.

As one of the perennial vegetable varieties grown in the south of Yangtze River in China, Brassica chinensis L. can be produced and supplied to the market all year round and has high economic value. However, there is little direct literature on postharvest heat treatment of Brassica chinensis L. In this study, Peroxidase (POD) was extracted from Brassica chinensis L. leaves and its enzymatic characteristics such as optimal pH, optimal temperature, catalytic activation energy, Km and Vmax, thermal stability and thermal denaturation activation energy were discussed. The results showed that with o-phenylenediamine as the hydrogen donor substrate of POD and hydrogen peroxide as the peroxide substrate, the optimal pH was 6.8, the optimal reaction temperature was 40°C and the activation energy of the catalytic reaction was 35.34 kJ/mol for POD in Brassica chinensis L. leaves. As a dual substrate reaction, when o-phenylenediamine was used as the substrate, the Km value of POD was 1.143 mmoL/L and Vmax was 142.86 U. When hydrogen peroxide was used as the substrate, the Km value of POD was 2.778 mmoL/L and Vmax was 111.11 U. Thermal inactivation studies showed first-order inactivation kinetic characteristics and the Arrhenius plot yielded a straight line with a slope equivalent to the thermal denaturation activation energy of POD at 199.54 kJ/moL. The thermal inactivation rate of POD varied significantly between 70 and 80°C (the rate constant k ranged from -0.446 to -0.970), indicating that the thermal denaturation of POD may occur between 70 and 80°C. It is expected that the above data would be beneficial to the optimization of quality control parameters in postharvest heat treatment and cold-chain transportation of Brassica chinensis L.