Effect of combined high pressure and thermal treatment on kiwifruit peroxidase

The effects of high pressure and heat treatments on peroxidase (POD) activity in kiwifruit were investigated. Pressure levels ranging from 200 to 600 MPa and temperatures varying from 10 to 50 °C were applied for up to 30 min. Assays were carried out on crude peroxidase in kiwifruit juice and on partially purified peroxidase in a model system. Pressures higher than 400 MPa could be combined with mild heat (⩽50 °C) to accelerate enzyme inactivation. Prolongation of the exposure time had no great effect after the first 15 min. The slope of POD in kiwifruit juice at 30 °C was slightly decreased compared with that in a model system. Furthermore, the optimum pH for POD was 6.0–8.5. The presence of POD isoenzymes and their difference in resistance to pressure were thought to be responsible for the final residual activity observed in this study.