High Pressure Inactivation of Polyphenoloxidases

Pressure stabilities of polyphenoloxidases (PPO) from apples, avocados, grapes, pears and plums were determined at pH 6-7. These PPOs differed in pressure stability, but all were rather pressure-stable. Inactivation of PPO from apple, grape, avocado and pear at room temperature (25°C) became noticeable at 600, 700, 800 and 900 MPa respectively, and followed first-order kinetics. Plum PPO was not inactivated at room temperature by pressures up to 900 MPa. For the two most pressure-stable PPOs, we investigated whether pressure stability would be reduced by the simultaneous application of mild heat. In case of plum PPO, activity reduction was detectable at 900 MPa and 50°C. Further temperature increase resulted in increase of the inactivation rate constant (E_a 63 kJ/mol). In case of pear PPO, temperature increase up to 35°C resulted in a 3-fold reduction of the inactivation rate constant. Only at higher temperatures, increase of the inactivation rate constant with increasing temperature was noted (Ea 120 kJ/mol).