Ohmic heating (OH) is defined as a process wherein electric current is passed through materials with the primary purpose of heating them. In OH there is no need to transfer heat through solid–liquid interfaces or inside solid particles once the energy is dissipated directly into the foods. A large number of actual and potential applications exist for OH, including blanching, evaporation, dehydration, fermentation, extraction, sterilization, pasteurization and heating of foods to serving temperature, including in the military field or long-duration space missions. Additionally to heating, research data suggests that the applied electric field under OH causes electroporation of cell membranes.

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Ohmic heating - a review.

Electrical conductivities of three vegetable and two meat samples were determined by subjecting them to a constant voltage power supply in a static ohmic heating device. Conductivities of vegetable samples were increased by soaking them in salt solutions, while soaking in water resulted in reduced conductivity due to leaching of electrolytes. Conductivities under ohmic heating conditions increased linearly with temperature. When field strengths were decreased, the conductivity-temperature curve gradually became nonlinear, and under conventional heating conditions, a sharp transition was observed.

ELECTRICAL CONDUCTIVITIES of SELECTED SOLID FOODS DURING OHMIC HEATING

Rice bran stabilization and rice bran oil extraction using ohmic heating.

Estimation of characteristic damage time of food materials in pulsed-electric fields

Summary
Ohmic heating is a food processing operation in which heat is internally generated within foods by the passage of alternating electric current. The process enables solid particles to heat as fast as liquids, thus making it possible to use High Temperature Short Time sterilization techniques on particulate foods. Ohmic heating rates are critically dependent on the electrical conductivities of the foods being processed, about which little information is available. This paper reports experiments to determine the changes in electrical conductivity which occur during ohmic heating of some common foods. A number of effects which occur during conventional heating, such as starch transition, melting of fats and cell structure changes, are shown to affect the electrical conductivity. In some cases the presence of an electric field induces enhanced diffusion of cell fluids in the food which increases the rate of change of conductivity with temperature above that found by conventional heating. Preheating is found to increase the electrical conductivity of some foods, making them acceptable for ohmic processing.

K. Halden

Papers

Changes in the electrical conductivity of foods during ohmic heating

Shape and conductivity effects in the ohmic heating of foods