Characterization and inactivation by thermal and pressure processing of strawberry (Fragaria ananassa) polyphenol oxidase:: A kinetic study

Polyphenol oxidase (PPO) was isolated from strawberries (Fragaria ananassa) and some of its biochemical characteristics were studied. The optimum pH for strawberry PPO activity was pH = 5.0. K(m)and V(max)values were 5.95 mm and 133.8 A(420nm)/min using a 50 mm catechol substrate solution. Kinetic studies showed that the thermal inactivation of strawberry PPO followed biphasic kinetics, resulting in an activation energy of 314.1 kJ/mol for the labile fraction and 321.3 kJ/mol for the stable fraction. Pressure/temperature inactivation of the stable fraction of strawberry PPO can be adequately described by a first-order model. Pressure and temperature were found to act synergistically, except in the high temperature-low pressure region where an antagonistic effect was observed. A second-degree polynomial model was successfully applied to describe the temperature/pressure dependence of the inactivation rate constants of the stable strawberry PPO fraction.