The effect of frequency and wave form on the electrical conductivity-temperature profiles of turnip tissue

Electrical conductivity (sigma) - temperature (T) curves were determined as a function of frequency and wave form of alternating current. Turnip cylinders were sandwiched between titanium electrodes and heated ohmically to 100C using four frequencies (4, 10, 25 and 60 Hz) and three wave forms (square, sine and sawtooth). The sigma-T curve shifted upward at 4 Hz for all wave forms. Curves were not significantly different at 10, 25 and 60 Hz for sawtooth and sine wave forms, while those for square waves were not significantly different at any of the frequencies tested. A comparison of wave forms showed that sigma-T curves for square waves were shifted downward significantly with respect to sine and sawtooth waves. Heating rate increased with decreasing frequency. Changes in vegetable tissue cellular structure are believed to be responsible for these results. Further research is necessary to characterize these mechanisms.