Polyphenoloxidase deactivation kinetics during ohmic heating of grape juice
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Date
2008
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Abstract
The heating method affects the temperature distribution inside a food, and directly modifies the time-temperature relationship for enzyme deactivation. Fresh grape juice was ohmically heated at different voltage gradients (20, 30, and 40 V/cm) from 20 °C to temperatures of 60, 70, 80 or 90 °C and the change in the activity of polyphenoloxidase enzyme (PPO) was measured. The critical deactivation temperatures were found to be 60 °C or lower for 40 V/cm, and 70 °C for 20 and 30 V/cm. Various kinetic models for the deactivation of PPO by ohmic heating at 30 V/cm were fitted to the experimental data. The simplest kinetic model involving one step first-order deactivation was better than more complex models. The activation energy of the PPO deactivation for the temperature range of 70-90 °C was found to be 83.5 kJ/mol. © 2007 Elsevier Ltd. All rights reserved.