Içier F.Yildiz H.Baysal T.2024-07-222024-07-22200802608774http://akademikarsiv.cbu.edu.tr:4000/handle/123456789/19032The 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.EnglishVitaceaeActivation energyEnzyme kineticsJoule heatingMathematical modelsEnzyme deactivationGrape juicePolyphenoloxidaseFruit juicesArticle10.1016/j.jfoodeng.2007.08.002