HEAT INACTIVATION KINETICS OF APPLE POLYPHENOLOXIDASE AND ACTIVATION OF ITS LATENT FORM

Heat inactivation kinetics of crude polyphenoloxidase (PPO) from six a pple cultivars (Golden Delicious, Starking Delicious, Granny Smith; Gl oster, Starcrimson and Amasya) were studied at three temperatures (68 degrees, 73 degrees and 78 degrees C). PPO activity initially increase d and then decreased with heat, following a first order kinetic model. Increase in activity indicated presence of latent PPO. Regression coe fficients for the linear portions of inactivation curves were computed to determine inactivation parameters. Reaction data at 78 degrees C r evealed that PPO in Amasya was the least and Starking Delicious the mo st heat-stable. Rate constants for heat inactivation at 78 degrees C r anged from 15.99-28.27.10(-2) min(-1). Activation energies varied betw een 54.7-77.2 kcal.mol(-1) with z values of 7.1-10.0C degrees. PPO in apples was generally more heat-stable than PPO in most fruits.