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The objective of this project was to identify factors that affect the temperature profile of food materials during ER heating, and to develop techniques for obtaining temperature profile during ER heating.
ER or ohmic heating is a promising technique for thermal processing of particulate foods. Theoretically, it is possible for food particulates with uniform electrical conductivity to heat evenly. The establishment of an approved process would be simplified because the liquid temperature could be used for lethality calculations. The objectives of the project were to develop techniques for measuring temperature profile of samples during processing and identify safety parameters.The project developed the multipoint (MP) probe and advanced the development of liquid crystal (LC) sheets and magnetic resonance imaging (MRI). They were capable of measuring 1-, 2- and 3-dimensional temperature profiles,respectively. The development of the MRI for temperature measurement was not finished while the other two were completed and are being used in various applications. Studies on tortuousity, shadowing effects and convection were conducted to understand safety factor in ER processing. Results showed that in food systems consisting of solids from various materials, shadowing effects could make the cold spot develop in solids with high electrical conductivity. This is an important finding since the rule of thumb in ER processing is that the cold spot develops in components with low electrical conductivity. A study on the effects of no, free and forced convections and conductivity ratios showed that the location of the cold spot (between solid and liquid) was not affected by convection but rather by conductivity ratio.