29D-2 |
Low-frequency dielectric changes in potato from ohmic heating: effect of end point temperature |
S. A. KULSHRESTHA and S. K. Sastry. Dept. of Food, Agricultural & Biological Engineering, Ohio State Univ., 590 Woody Hayes Dr., 260 Agricultural Engineering Bldg., Columbus, OH 43210-1058 Electropermeation of cell membranes of raw plant tissue is potentially useful in drying and juice extraction processes. The objective of this study was to examine the effect of ohmic heating on dielectric spectra of potato from 100 Hz to 20 kHz after heat treatments ranging from final temperatures of 25°C -70°C. The effect of ohmic heating on cell membranes of potato 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 to various temperatures ranging from 30°C to 70°C either conventionally or ohmically After cooling to 25°C, the ohmically heated samples had significantly higher conductivity 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.
Session 29D, Food Engineering: Thermal processes
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