Effects of Radio-Frequency Energy on Peroxidase Inactivation and Physiochemical Properties of Stem Lettuce and the Underlying Cell-Morphology Mechanism

This paper investigated the effects of radio-frequency (RF) energy and conventional hot-water blanching (95 degrees C for 2 min) on the peroxidase (POD) activity, physiochemical properties, and changes in the cellular morphology of stem lettuce. The relative residual POD activity significantly decreased (P < 0.05) from 66.03% to 6.46% with increased RF heating temperature (65 degrees C-85 degrees C). The weight loss (3.06%-7.64%), color, texture, relative electrolyte leakage (23.45%-67.90%), and residual vitamin C content (72.22%-16.67%) significantly changed (P < 0.05) with increased RF heating temperature (65 degrees C-85 degrees C). Micrographs indicated that the changes in physiochemical property can be attributed to the destruction of cell membranes, loss of cell turgor, reduced rigidity of cell walls, and loose adhesion between adjacent cells. Samples treated by RF heating at 75 degrees C showed lesser cell damage and better nutrient retention than those treated by hot-water blanching at a similar level of POD inactivation.