17G-6 |
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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 Electrical properties of vegetable tissue during moderate electric field (MEF) treatment are thought to be related to changes in the permeability of cell membranes upon exposure to an electric field. Electric treatments of fruits and vegetables have significant potential in improving various process operations, but greater understanding of the underlying mechanisms is necessary. The objective of this study was to monitor changes in electrical conductivity of potato in the very early stages of MEF treatment. Potato slices were placed between platinized electrodes and exposed to alternating electric fields of up to 120 V/cm at 60 Hz. Current and applied voltage were measured with an oscilloscope with a resolution of hundreds of picoseconds. In particular, we were attempting to observe phenomena at very short time scales during treatment. The conductance increased most during the first half cycle of the alternating electric field, followed by a steady rise with subsequent cycles. This indicates that cells are very sensitive to electric fields, and breakdown is observed at time scales on the order of milliseconds, explaining the effect of low frequencies that has been observed in our previous work. This also indicates that nonthermal mechanisms play a part in the increase in conductivity seen in vegetable tissue during moderate electric field processing, as the temperature increase during the first half cycle is very small. There were no abrupt peaks of conductance at higher voltages, where resistance current is dominant, indicating that a number of cell breakdown events occur during each cycle, eventually leading to increased conductivity occur over a several cycles. Charging current was dominant as voltage passed through the zero point, indicating significant capacitive effects. This study is part of the foundation for research in the area of moderate electric field processing of plant foods.
Session 17G, Food Engineering: Physical, chemical and electrical properties
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