Changes in permeability of moderate electric field (MEF) treated vegetable tissue over time

A microscopic examination of beet tissue given a moderate electric field treatment shows that some cells lose their membrane selectivity while others remain intact. Raw, thawed, or precooked potato cylinders were chilled, and then warmed to 25 degrees C by either allowing them to equilibrate or by MEF treatment. The conductivity from 100 Hz to 20 kHz and apparent dielectric constant from 100 Hz to 5 kHz was initially not significantly different between raw-untreated samples and raw-MEF treated samples, but over 24 h, that of the raw-MEF treated samples increased while that of the raw-untreated samples remained constant. No such distinct pattern emerged from the thawed or precooked samples. The apparent dielectric constant of raw-MEF treated potato above 5 kHz was not significantly different from raw-untreated potato and higher than thawed and precooked potato. None of the samples showed marked changes in dielectric constant at 5-20 kHz over the 24 hour period. Apparently, even mild electrical treatments permeabilize vegetable tissue, permitting enhanced diffusion. This work has implications in improving nonthermal permeabilization processes for eukaryotic cells. which can be used in fruit and vegetable drying and juice extraction operations. (C) 2009 Elsevier Ltd. All rights reserved.