Ultrasonic Ohmic Heating in Food Processing

The demand for gentle yet effective processing technologies in the food sector has intensified, driven by the need to balance microbial safety with the preservation of nutritional and sensory qualities. Conventional thermal treatments often rely on surface-to-core heat transfer, which is slow and prone to non-uniformity. Ohmic heating, based on the conversion of electrical energy into heat directly within the food matrix, addresses this challenge by enabling rapid and volumetric heating. When coupled with ultrasound, the process is further enhanced: ultrasonic cavitation promotes cell disruption, homogenization, and mass transfer, thereby overcoming conductivity variations that can otherwise create localized heat channels.

Ultrasonic Ohmic Heating – Mild, Yet Very Efficient

Ultrasonic ohmic heat extraction combines uniform volumetric heating with mechanical homogenization by ultrasound to achieve efficient food processing under comparatively gentle conditions. Unlike conventional ohmic heating, which may generate localized heat channels and thermal degradation (i.e. overheating), the addition of ultrasound promotes cavitation and microstreaming that homogenize conductivity and distribute heat more evenly. This synergy enables rapid extraction at lower effective thermal loads, preserving heat-sensitive compounds while reducing overall energy demand. As a result, ultrasonic ohmic heating emerges as a mild yet powerful approach for producing high-quality food products.

Ultrasonic Ohmic Heating – Many Applications in Food Processing

Ultrasonic ohmic heating has been investigated across a broad range of food processing applications. In pasteurization and sterilization, the technique ensures fast and uniform microbial inactivation while maintaining vitamins, flavors, and textural attributes. In stabilization processes, such as enzyme inactivation or seed decontamination, it provides precise control over treatment intensity. The method is particularly promising for extraction – whether of essential oils, plant proteins, or bioactive compounds – where ultrasound-induced cavitation accelerates release and ohmic heating facilitates efficient solvent penetration. It has also been applied in the processing of liquid and semi-solid foods, including dairy products, fruit pulps, juices, and emulsions, where uniform heating and mixing are critical.

 
The main applications of ultrasonic ohmic heating in the food industry include:

1. Pasteurization and Sterilization: rapid, uniform microbial inactivation while preserving sensory and nutritional quality.
2. Extraction of Bioactive Compounds and Essential Oils: ultrasound-induced cavitation combined with ohmic electroporation accelerates release of phytochemicals, proteins, and lipids.
3. Blanching of Fruits and Vegetables: effective enzyme inactivation with minimal loss of color, flavor, or vitamins.
4. Dehydration and Evaporation Processes: accelerated moisture removal and energy savings in drying or concentration steps.
5. Fermentation Support: controlled heating and enhanced mass transfer can improve microbial performance and yield.
6. General Heating of Liquid and Semi-Solid Foods: homogeneous temperature distribution in dairy, juices, purees, and emulsions, avoiding hot spots.

The Advantages of Ultrasonic Ohmic Heating for the Food Industry

For the food industry, the advantages of ultrasonic ohmic heating are manifold. The technology reduces processing time and energy consumption, offers highly uniform heating even in heterogeneous matrices, and minimizes thermal degradation of heat-sensitive compounds. Because both heating and ultrasound effects are generated within the food itself, the process eliminates the need for large external heat exchangers and lowers maintenance costs. Most importantly, it aligns with the growing emphasis on clean-label products and sustainable processing by reducing reliance on harsh treatments or chemical additives. As such, ultrasonic ohmic heating stands out as a powerful tool to meet future demands for safe, nutritious, and environmentally responsible food production.
 

The Advantages

1. Uniform Heating: Ultrasound counteracts the formation of heat channels, ensuring homogeneous temperature distribution in heterogeneous foods.
2. Rapid Processing: Combined effects of ohmic heating and ultrasound shorten pasteurization, sterilization, and extraction times.
3. Energy Efficiency: Lower overall energy consumption compared with conventional thermal treatments.
4. Nutrient and Flavor Preservation: Milder thermal loads preserve vitamins, antioxidants, and volatile flavor compounds.
5. Enhanced Extraction: Electroporation and cavitation accelerate release of bioactive compounds, essential oils, and proteins.
6. Food Safety: Effective microbial and enzymatic inactivation with minimal quality loss.
7. Scalability and Flexibility: Applicable to liquid and semi-solid foods.
8. Clean Processing: Solvent-free, chemical-free, and aligned with sustainable “clean label” production.

Ultrasonic Electrodes for Improved Ohmic Heating in Food Processing

Hielscher ultrasonic electrodes (sono-electrodes) offer a distinct advantage in ohmic heating because they integrate two complementary mechanisms in a single setup: electrical current delivery and ultrasonic agitation. While the electrode applies the alternating current needed for volumetric Joule heating, its simultaneous oscillation at 20 kHz generates cavitation, microstreaming, and shear forces that disrupt plant cell walls and homogenize the medium. This dual action minimizes the formation of heat channels, ensures more uniform electrical conductivity, and thereby produces even heating throughout the sample. At the same time, the ultrasonic extraction effect accelerates mass transfer and promotes the release of intracellular compounds, further enhancing yield and quality. In commercial contexts, the Hielscher UIP2000hdT electrode system (2000 W per electrode) provides the robustness required for continuous industrial production, whereas smaller setups such as the UP100H (100 W) and VialTweeter serve as flexible tools for laboratory-scale research and process optimization.

The table below gives you an indication of the approximate processing capacity of our Ohmic heating sonicators / ultrasonic electrodes:

Design, Manufacturing and Consulting – Quality Made in Germany

Hielscher ultrasonicators are well-known for their highest quality and design standards. Robustness and easy operation allow the smooth integration of our ultrasonicators into industrial facilities. Rough conditions and demanding environments are easily handled by Hielscher ultrasonicators.

Hielscher Ultrasonics is an ISO certified company and put special emphasis on high-performance ultrasonicators featuring state-of-the-art technology and user-friendliness. Of course, Hielscher ultrasonicators are CE compliant and meet the requirements of UL, CSA and RoHs.