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The technical feasibility of ohmic heating was evaluated for viscous liquids in static ohmic heating cells in three stages. First, electrical conductivities and time/temperature profiles were measured and compared for selected hydrocolloids (carrageenan, gelatin, pectin, starch and xanthan) in water at various concentrations (1--6%). Of the thickening agents examined, carrageenan gave the highest value for electrical conductivity and the shortest time to raise the temperature from 20 to 100°C. It was followed by xanthan. Pectin and gelatin samples were found to exhibit lower, but similar electrical conductivities and heating profiles. Starch samples had the lowest electrical conductivity and the temperature of starch solutions never exceeded 62°C within the specified time limit of 10000 s. / In the second stage, the effect of salt and acid concentration was evaluated on electrical conductivities and time/temperature profiles of the above selected hydrocolloids in water solutions at a concentration necessary to achieve a similar apparent viscosity of 0.2 Pa.s at 300 s-1 and 20°C (carrageenan 1.7%, pectin 2.5%, starch 4.3% and xanthan 2%). / In the third stage, measurements of electrical conductivities, time/temperature and heating rate profiles were performed applying six voltage gradients (5.26, 7.14, 13.16, 17.86, 21.05 and 25 V/cm), with two electrode cross-sectional surface areas (19.84 and 37.95 cm2) and the electrodes separated at three specific distances (10.05, 14.33 and 20.01 cm) at 150 V. Applied voltage gradients had a major effect on temperature and heating rate profiles but no effect on electrical conductivities. / Rheological properties of carrageenan, pectin, starch and xanthan solutions were investigated at various temperatures (20--80°C) and concentrations (carrageenan 1.5, 1.7 and 1.9%; pectin 2.3, 2.5 and 2.7%; starch 3.8, 4 and 4.2%; xanthan 1.6, 1.8 and 2%) in the presence of 1% salt. Both temperature and concentration influenced the rheological properties of solutions. / Finally, electrical conductivity measurements and rheological properties of starch at 4% and 1% salt were used as input to evaluate a theoretical model for the electrical, thermal and flow behaviour in a continuous ohmic heating unit. (Abstract shortened by UMI.)

Ohmic heating is an electrical resistance heating resulting from the passage of electrical current through an electrically conductive material offering some resistance. Most food products possess sufficient electrical conductivity to be able to take advantage of ohmic heating. This research was undertaken to evaluate the quality changes associated with fine ham emulsions prepared under ohmic heating conditions as compared to those produced by conventional heating. / In the first part of the study, kinetics of quality changes (color, texture, water holding capacity, cooking loss and water activity) associated with fine ham emulsion subjected to conventional heating conditions were evaluated. The second part of the study was to standardize ohmic heating conditions for achieving target time-temperature combinations. It was desired to achieve cooking conditions (temperature come-up and hold times) both similar to and faster than conventional heating so that meaningful quality comparisons could be made between the two. / The final part of the study was to compare the quality changes of fine ham emulsion subjected to ohmic heating under different rates, and to compare them with conventional heating. (Abstract shortened by UMI.)

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