| Diffusion of beet dye from beet cubes was measured during a 3 min. moderate electric field (MEF) process using frequencies ranging from 0 (direct current) to 5000 Hz, and field strengths ranging from 0 (conventional heating) to 23.9 V/cm, while maintaining steady-state temperature at 45°C throughout the process. Diffusion increased with electric field strength and decreased with frequency. There was no enhanced diffusion from an agar cube or from previously frozen beet tissue. Electropermeabilization is suggested as the mechanism for enhanced diffusion.; 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 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.; Microscopy shows that in beet tissue given a moderate electric field treatment, some cells lose their membrane selectivity while others remain intact. Raw, thawed, or precooked potato cylinders were chilled, and then warmed to 25°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 the same between raw, untreated samples and raw, MEF treated samples, but over 24 hours, 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 5kHz was the same as 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. |
