Low-frequency dielectric changes in cellular food material from ohmic heating: Effect of end point temperature

The effect of ohmic heating on cell membranes of cellular food material was investigated by measurement of dielectric spectra from 100 Hz to 20 kHz. Cylinders of potato were placed in a glass static ohmic heater and heated, either conventionally or ohmically, to various temperatures ranging from 30 degrees C to 70 degrees C. After cooling to 25 degrees C, the ohmically heated samples had significantly higher electrical conductivity than conventionally heated samples at all measurement frequencies for endpoint temperatures of 40 degrees C and 50 degrees C. At low frequencies, the apparent dielectric constant was also higher for these samples, but at high frequencies, the reverse pattern was shown. The ohmically heated samples apparently have greater membrane permeability than conventionally heated samples when heated to temperatures below 60 degrees C. This is reflected in the diffusion of KCl solution into the tissues, which is faster at higher endpoint temperatures. (c) 2006 Elsevier Ltd. All rights reserved.