Optimization and validation of PEF processing conditions to inactivate oxidative enzymes of grape juice

Abstract

White grape juice was processed using high intensity pulsed electric fields (PEF). The effect of this preservative technology on polyphenoloxidase (PPO) and peroxidase (POD) as well as on refractometric index, sugar content, pH, acidity and density was studied. In addition, the use of the response surface methodology as a tool to obtain accurate information and provide predictions of enzymatic depletion on real foods was assessed. The studied PEF factors were electric field strength, pulse frequency, pulse width and total treatment time. Inactivation values of 100% for PPO and up to 50% for POD were achieved after different PEF treatments. The activity depletion was strongly dependent on the evaluated factors, mainly PEF treatment time. A predictive equation for each residual activity covering the whole range of experimentation was developed and their results were confirmed against a set of validation experiments. In addition, predictions obtained from the developed response surfaces and exponential kinetic models were comparable. In conclusion, PEF treatments depleted PPO and POD activities of grape juice although it was observed that grape POD was less sensible than PPO to PEF technology. Response surface methodology allows analysing and optimizing the PEF treatments as well as predicting their results with very few experiments.