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S. K. SASTRY, Food, Agricultural & Biological Engineering, Ohio State University, 206 Agricultural Engineering, 590 Woody Hayes Drive, Columbus, OH 43210, D. R. HELDMAN, Heldman Associates, 8 Shadow Ridge Circle, Newtown, CT 06470, J. T. Barach, National Food Processors Association, 1350 I Street, N.W. Suite 300, Washington, DC 20005, A. K. Datta, Department of Agricultural & Biological Engineering, Cornell University, 208 Riley-Robb Hall, Ithaca, NY 14853, and P. M. Davidson, Food Science & Technology, University of Tennessee Knoxville, 201 McLeod Hall, P.O. Box 1071, Knoxville, TN 37901-1071.

Ohmic heating is defined as a process wherein (primarily alternating) electric currents are passed through foods or other materials with the primary purpose of heating them. The heating occurs in the form of internal energy generation within the material. Inductive heating is a process wherein electric currents are induced within the food or other material due to the presence of oscillating electromagnetic fields generated by electric coils in the vicinity of this material; with the primary purpose of heating the said material. Information on inductive heating is extremely limited. Thus this discussion will principally focus on ohmic heating.

The principal mechanisms of microbial inactivation are expected to be thermal in nature. Processors should be able to file processes based on thermal inactivation. However, it may be of interest on occasion to use a milder process, such as pasteurization.

Early literature on kinetics was inconclusive, since temperature had not been conclusively eliminated as a variable. However, recent literature that has eliminated thermal differences indicates that a mild electroporation mechanism may occur. The principal reason for the additional effect of ohmic treatment may be due to the low frequency (50-60 Hz) of, which allows cell walls to build up charges, and form pores. This is in contrast to high-frequency methods such as radiofrequency or microwave heating, where the electric field is essentially reversed before sufficient charge buildup. While some evidence exists for nonthermal effects of ohmic heating, a larger body of research is needed to more fully understand the mechanism for various microorganisms. For most ohmic processes, which rely on heat, it may be unnecessary for processors to claim this effect in their process filings. However, it may be possible for future processes to be reduced; in which case sufficient data will be necessary.