Ohmic heating is an advanced thermal processing method wherein the food material, which serves as an electrical resistor, is heated by passing electricity through it. Electrical energy is dissipated into heat, which results in rapid and uniform heating. Ohmic heating is also called electrical resistance heating, Joule heating, or electro-heating, and may be used for a variety of applications in the food industry.
During conventional thermal processing, either in cans or aseptic processing systems for particulate foods, significant product quality damage may occur due to slow conduction and convection heat transfer. On the other hand, ohmic heating volumetrically heats the entire mass of the food material, thus the resulting product is of far greater quality than its canned counterpart. It is possible to process large particulate foods (up to 1 inch) that would be difficult to process using conventional heat exchangers. Additionally, ohmic heater cleaning requirements are comparatively less than those of traditional heat exchangers due to reduced product fouling on the food contact surface.
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Ohmic heating can be used for heating liquid foods containing large particulates, such as soups, stews, and fruit slices in syrups and sauces, and heat sensitive liquids. The technology is useful for the treatment of proteinaceous foods, which tend to denature and coagulate when thermally processed. For example, liquid egg can be ohmically heated in a fraction of a second without coagulating it. Juices can be treated to inactivate enzymes without affecting the flavor. Other potential applications of ohmic heating include blanching, thawing, on-line detection of starch gelatinization, fermentation, peeling, dehydration, and extraction.
Like thermal processing, ohmic heating inactivates microorganisms by heat. Additional non-thermal electroporation type effects have been reported at low-frequency (50–60 Hz), when electrical charges can build up and form pores across microbial cells, however, it is not necessary to claim such effects since heating is the main mechanism.
The shelf life of ohmically processed foods is comparable to that of canned and sterile, aseptically processed products.
Yes. Some major equipment suppliers providing commercial size ohmic heaters for the food industry include Emmepiemme SRL in Piacenza, Italy, and Capenhurst, United Kingdom. An additional major supplier is likely to enter the market in 2006. Information on available capacities of commercial equipment depends on the application, and information may be obtained from the suppliers.
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A number of processing plants currently produce sliced, diced, and whole fruit within sauces in various countries, including Italy, Greece, France, Mexico, and Japan. In the United States, ohmic heating has been used to produce a low-acid particulate product in a can, as well as pasteurized liquid egg.
Yes. This process uses ordinary electricity. No emissions are produced at the point of use. One emerging application of ohmic heating is fruit peeling, which may greatly reduce the use of lye that is common to such operations, and results in environmental benefits.
An economic analysis conducted at the University of Minnesota in the early 1990s indicated that ohmic heating would be economically viable for premium quality foods. However, costs of ohmic systems have decreased greatly since that time, and the range of products for which ohmic heating is economical has expanded considerably.
For in-container processing, the requirements are similar to that of traditional thermal processing in the United States. For continuous flow processing with aseptic packaging, the approaches are currently in development in a project funded by the USDA National Integrated Food Safety Initiative. The Food and Drug Administration (FDA) is responsible for evaluating and monitoring the safety of ohmically processed foods, unless the product contains a specified minimum amount of meat and poultry. In such cases, it falls under USDA’s purview.
An industrial scale ohmic heating pilot plant facility is available at The Ohio State University’s Department of Food, Agricultural and Biological Engineering. Food processors are invited to take advantage of the expertise of OSU faculty members and facilities to conduct confidential product evaluations for food safety, quality, and shelf life, and to obtain guidance on product development. The resources at OSU can be accessed for a reasonable fee.