Nonthermal inactivation effects on oxidative enzymes in grape juice influenced by moderate electric fields: Effect of constant exposure electrical treatments combined with temperature

Inactivation of polyphenol oxidase (PPO) and peroxidase (POD) enzymes in fresh grape juice was studied by subjecting the juice to moderate electric field (MEF) treatments of 82 and 87 V/cm field strengths. We used an electro-processing device that was built to minimize ohmic heating and enhance cooling during application of electric fields. Kinetic studies indicate that the MEF treatments increase the inactivation of both enzymes at 65 and 75 °C, compared to the corresponding control treatments without electric fields. The increase in the inactivation becomes statistically significant (P ≤ 0.05) in the MEF treatment at 75 °C. Molecular motion simulations of PPO and POD enzymes correlate with the experimental results. The study results further indicate the efficacy of MEF treatments on the nonthermal inactivation of enzymes, which are held at or near their thermal inactivation threshold temperatures (≤80 °C for PPO and POD).