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The effects of temperature and soluble solids on degradation of anthocyanins in sour cherry concentrate were determined over temperature ranges (-18 to 37)"C and 50 to 80°C. Anthocyanin degradation could be modeled as a first-order rate reaction, with rates of 33.97 X lo-' .hr-1 (lS"Brix), 59.19 X lo-' .I@ (45"Brix) and 97.14 X lo+ .hr-' (71"Brix) at 80°C. Temperature dependence of reaction was described by the Arrhenius relationship. Activation energy for a solids content of U-71' Brix ranged from 16.37-19.14 kcal.mole-' with an average of 17.45 kcaI.mole-1

Heat inactivation kinetics of crude polyphenoloxidase (PPO) from six apple cultivars (Golden Delicious, Starking Delicious, Granny Smith; Gloster, Starcrimson and Amasya) were studied at three temperatures (68Њ, 73Њ and 78ЊC). PPO activity initially increased and then decreased with heat, following a first order kinetic model. Increase in activity indicated presence of latent PPO. Regression coefficients for the linear portions of inactivation curves were computed to determine inactivation parameters. Reaction data at 78ЊC revealed that PPO in Amasya was the least and Starking Delicious the most heat-stable. Rate constants for heat inactivation at 78ЊC ranged from 15.99-28.27 ⅐ 10 Ϫ2 min Ϫ1 . Activation energies varied between 54.7-77.2 kcal ⅐ mol Ϫ1 with z values of 7.1-10.0CЊ. PPO in apples was generally more heat-stable than PPO in most fruits.

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