86A-11

P. WONGSA-NGASRI, Food, Agricultural and Biological Engineering, Ohio State University, 101 Curl Dr. #532, Columbus, OH 43210 and S. K. Sastry, Food, Agricultural and Biological Engineering, OSU, 590 Woody Haye Dr., Columbus, OH 43210.

Arcing phenomena on carbon electrode surfaces in ohmic heating were investigated with isolated soy protein and modified starch solutions. The inlet temperature of samples, electric field strengths, and composition were variables. The safety zones of processing were found. Arcing time increased with decreasing electric field strength or inlet temperature at the same protein content, and decreased with increasing protein content at the same electric field strength and inlet temperature. However, the effect of starch content was not clear-cut.

The objective was to study the effect of temperature, electric field strength, current density, and composition on the occurrence of arcing during ohmic heating.

Inlet temperature, applied voltage, and protein and starch contents were investigated by heating under various combinations. The parameters were varied in successive experiments until arcing was observed. The time duration from the application of voltage to the arcing point was recorded. Voltage, current, and temperature between electrodes were monitored and recorded by video camera and computer. An arcing diagram was plotted to present results.

Arcing diagrams showed that the higher the temperature, the lower the electric field strength needed for arcing. The diagrams roughly demarcate three areas: arcing zone, safety zone, and critical zone. At the same operating condition, the higher the protein content, the easier the onset of arcing. At the same electric field strength, the arcing time exponentially decreased with increasing inlet temperature of sample. Starch effects were not clear-cut.

The relationship between inlet temperature, electric field strength, protein/starch content, and arcing occurrence can be used to guide food processors to operate an ohmic heating process without arcing.