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 °C to 70 °C. After cooling to 25 °C, the ohmically heated samples had significantly higher electrical conductivity than conventionally heated samples at all measurement frequencies for endpoint temperatures of 40 °C and 50 °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 °C. This is reflected in the diffusion of KCl solution into the tissues, which is faster at higher endpoint temperatures.Industrial relevanceThis paper deals with electro-permeabilisation of biological cells during ohmic heating of plant foods. It is of industrial interest and relevance to evaluate the electroporation of cellular material during ohmic heating and to establish a comparison of the effectiveness of membrane permeabilisation via pulsed electric field treatment (PEF), ohmic heating (OH) and thermal processing, as well as combinations of PEF or OH with mild heat treatment. Such data would allow to develop the most energy effective process with resulting optimum product functionality, safety and nutritial quality characteristics.