High-Frequency-Heating Characteristics of Vegetable Tissues Determined from Electrical-Conductivity Measurements

An investigation was made to determine the high-frequency heating characteristics of certain vegetable tissues by means of electrical-conductivity measurements. The specific conductivities of potato, carrot, apple, and peach at 25°C were found to be of the same order of magnitude and range from about 3 × 10
^-4
ohm
^-1
cm
^-1
at 10
³
cps to 5 × 10
^-3
ohm
^-1
cm
^-l
at 4 ×10
⁷
cps. Variation in the temperature from -80 to +30°C is accompanied by a gradual rise in conductivity with a sharp tenfold increase at the melting point of ice. For temperatures between the melting point and 30°C, the conductivity increases approximately 2 per cent per °C. Investigation of the effect of the water content on the specific conductivity showed, in the case of carrot, that a reduction in the water content from a value of 80 per cent, characteristic of the raw tissue, to a value of 1.5 per cent is accompanied by a ten-thousandfold (at 3 × 10
⁷
cps) decrease in specific conductivity. These results are discussed briefly in relation to industrial applications of the high-frequency-heating method in the food and pharmaceutical industries.