Inactivation of tomato juice peroxidase by high-intensity pulsed electric fields as affected by process conditions

A response surface was used to establish the high-intensity pulsed electric fields (HIPEF) conditions in processing tomato juice to obtain the greatest peroxidase (POD) inactivation. Keeping constant the electric field strength at 35 kV/cm and the temperature below 35 °C, the treatments were set at pulse frequency from 50 to 250 Hz, pulse width from 1 to 7 μs and treatment time from 1000 to 2000 μs, using monopolar or bipolar mode. The effect of these parameters on POD inactivation was evaluated through a second order model that adequately fitted the experimental data (p = 0.0001), with a determination coefficient (R2) of 0.85. HIPEF treatment resulted to be more effective in bipolar than monopolar mode to reduce POD activity and the longer the treatment time, the greater the reduction on the enzyme activity. A pulse frequency of 200 Hz was enough to reach a minimum value of residual POD activity. The significant interaction term pulse frequency and treatment time was included in the model, showing that different combinations of both variables can lead to the same level of residual POD activity. The effect of pulse width was enhanced by using a bipolar mode, being feasible to maximize POD inactivation selecting pulse width higher than 5.5 μs in bipolar mode.