Ascorbic acid (vitamin C) degradation during electrical and conventional heating was studied to determine if the presence of an electric field altered the rate of degradation. Experiments were peiformed using a static ohmic heating apparatus, and heating histories were matched using applied voltage in the electrical case and hot oil in the conventional case. A statistical analysis showed that electric field has no significant effect on ascorbic acid degradation. Pseudo first order degradation kinetics were observed for both conventional and ohmic cases. the activation energy and frequency factor for the conventional case was 12.6 kcal/mol and 19.95 × 105 min‐1, respectively; for the ohmic case, values were 12.5 kcal/mol and 19.59 × 1O5 min‐1. the effect of electrolysis on ascorbic acid degradation was also examined. Gas production and dissolution appeared

Electrical conductivity (σ) – 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 σ‐T curve shifted upward at 4 Hz for all wave forms. Curses 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 σ‐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.

Liquid‐to‐particle convective heat transfer coefficients were measured during continuous flow through tubes, using an experimental technique in which a thermocouple was moved at the same speed as the particle. Water was used as the carrier fluid and transducer particles were made hollow to approximate densities of real food particles. Results from over 250 experimental runs over a fluid Reynolds number range from 7300 to 43600, showed that the convective coefficient was increased significantly with increasing fluid flow rate and particle to tube diameter ratio. Convective coefficient values ranged from 688 to 3005 w/m20C depending on the experimental conditions. Dimensionless correlations obtained between the Nusselt number, particle Reynolds number, particle to tube diameter ratio, and the particle Froude number yielded R2 values ranging from 0.82 to 0.92 depending on the complexity of the relation.

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Ohmic heating has been shown to alter mass transfer properties of fruit and vegetable tissue. Diffusion of beet dye from beetroot tissue into a fluid was studied during conventional and ohmic heating as a function of steady‐state temperature. The volume of beet dye diffusing into solution during ohmic heating was enhanced with respect to conventional heating at 42C and 58C, but not at 72C. This can be explained by examining the differences in electrical conductivity of beet tissue at these temperatures during conventional and ohmic heating. At 42 and 58C, the electrical conductivity of beet tissue heated ohmically is higher than the electrical conductivity of beet tissue heated conventionally. At 72C, the electrical conductivities of beet tissue during conventional and ohmic heating are equal. The extent of diffusion in the ohmic case is also positively correlated with applied voltage. These results suggest that food processes involving mass transfer can be enhanced by choosing conditions in which the electrical conductivity of a sample under ohmic conditions is maximized.