The objective of this study was to investigate the effect of Moderate Electric Fields (MEF) on pectin methylesterase (PME) activity in tomatoes. Inactivation kinetics parameters of MEF and conventional thermal treatments were determined for samples of identical prior source and pretreatment history, subjected to nearly identical linearly increasing temperature histories. The presence of electric field (60 Hz, sine wave) resulted in activation of PME at 70 (+/- 1) degrees C, and accelerated inactivation at higher temperatures. This effect increased with field strength. The results may be interpreted in light of molecular motion calculations for PME, which suggest that enzyme molecules subjected to an oscillating electric field experience electrophoretic motion, and behave as if at a slightly higher temperature than that of the bulk, resulting in an activating effect at lower temperatures, but an inactivation effect at higher temperatures. (C) 2016 Elsevier Ltd. All rights reserved.