title: Combined effect of temperature and pulsed electric fields on apple juice peroxidase and polyphenoloxidase inactivation.
abstract: 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°C; 26s). 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°C, and a PEF treatment time of 100μs at 40kV/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).
authors.affiliation: School of Agriculture Food Science and Veterinary Medicine, College of Life Sciences, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Joerg
authors.initials: J
authors.lastname: Riener
authors.affiliation: School of Agriculture Food Science and Veterinary Medicine, College of Life Sciences, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Francesco
authors.initials: F
authors.lastname: Noci
authors.affiliation: School of Agriculture Food Science and Veterinary Medicine, College of Life Sciences, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Denis A
authors.initials: DA
authors.lastname: Cronin
authors.affiliation: School of Agriculture Food Science and Veterinary Medicine, College of Life Sciences, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Desmond J
authors.initials: DJ
authors.lastname: Morgan
authors.affiliation: School of Agriculture Food Science and Veterinary Medicine, College of Life Sciences, University College Dublin, Belfield, Dublin 4, Ireland. Electronic address: james.lyng@ucd.ie.
authors.forename: James G
authors.initials: JG
authors.lastname: Lyng
keywords: Apple juice; Kinetics; Peroxidase; Polyphenoloxidase; Pulsed electric field