Effects of pulsed electric field processing on apple and pear polyphenoloxidases

The feasibility of inhibiting polyphenoloxidase from apple and pear by pulsed electric field processing was evaluated. These treatments significantly lowered polyphenoloxidase activity of enzyme extracts from apple (Golden delicious var.) and pear (Blanquilla var.). Exponential decay pulses were generated by a laboratory scale electric pulse generator and applied in bipolar mode. Pulse duration was 0.02 ms and electric field intensities were up to 24.6 kV/cm. The temperature of samples never exceeded 15 degreesC during pulsed electric field processing treatments. Polyphenoloxidase activities were reduced up to 3.15% and 38.0% initial value in apple extract at 24.6 kV/cm and pear extract at 22.3 kV/cm both for 6 ms total treatment time, respectively. Apple and pear polyphenoloxidase exposed to pulsed electric field processing diminishes their activities following first order kinetics. Rate constants ranged from 132 to 440 mus(-1) for apple polyphenoloxidase, whereas for pear polyphenoloxidase they ranged from 26 to 173 mus(-1) and changed exponentially with the applied electric field intensity, Residual polyphenoloxidase activity was correlated to energy density by an exponential decay model.