Combined effect of temperature and pulsed electric fields on apple juice peroxidase and polyphenoloxidase inactivation

Pulsed electric fields (PEF) were applied to freshly prepared apple juice using a laboratory scale continuous PEF system to study the feasibility of inactivating peroxidase (POD) and polyphenoloxidase (PPO). Square wave PEF using different combinations of electric field strength, pre-treatment temperature and treatment time were evaluated in this study and compared to conventional pasteurisation (72 degrees C 26 s). Inactivation curves for the enzyme were plotted for each parameter and inactivation kinetics were calculated. Results showed the highest level of decrease in the enzymatic activity of 71% and 68%, for PPO and POD, respectively, were obtained by using a combination of preheating to 50 degrees C, and a PEF treatment time of 100 mu s at 40 kV/cm. This level of inactivation was significantly higher (P < 0.05) than that recorded in juice processed by conventional mild pasteurisation where the activity of PPO and POD decreased by 46% and 48%. respectively. The kinetic data for the inactivation of both enzymes could be described using a 1st-order model (P < 0.001). (C) 2007 Elsevier Ltd. All rights reserved.