Journal of food science vol:70 issue:5 pages:E301-E307
Thermal and/or high pressure inactivation of polyphenol oxidase (PPO), isolated from grapes (var. Victoria, South Africa) was studied as a function of pH. Temperature as well as pressure stability increased with increasing pH from 3 to 6. Both thermal (pH range, 3 to 6) and thermal-high pressure inactivation (pH = 3) of the enzyme followed 1st order kinetics. The z(t) value and activation energy, both reflecting the temperature dependency of the inactivation rate constant, respectively, slightly decreased and increased with increasing pH from 3 to 6. The thermal-high pressure inactivation of Victoria grape PPO was kinetically investigated in a model system at pH 3.0. A 3rd-degree polynomial model was successfully applied to describe the temperature/pressure dependence of the inactivation rate constants. Pressure and temperature were found to act synergistically, except in the high temperature (>= 45 degrees C)-low pressure (<= 300 MPa) region where an antagonistic effect was observed.