Ohmic Tempering of Antarctic Krill (Euphausia superba) Blocks: Electrical Conductivity Determination and Computer Simulation Approach

Antarctic krills are rapidly frozen onboard into blocks, and therefore, developing technologies that can enable rapid and uniform semi-thawing and tempering to prevent enzymatic reactions is essential to enhance their quality and commercial value. We evaluate the application of ohmic tempering (OT) in this study. Experimental blocks (4 × 4 × 4 cm³) are processed under OT at 20 kHz and several constant and variable voltages from −30 C to −5°C. Electrical conductivities of the Antarctic krill block and the block's solution are determined in temperature and frequency ranges of −30 C–0°C and 50 Hz to 200 kHz. Better temperature uniformity and reduced OT time are obtained by fine-tuning the voltage in four steps from 400 to 50 V based on the electrical conductivity (EC) changes to avoid overheating. Compared to conventional tempering methods (air, running water, and low temperature (inside a refrigerator)), OT results in a faster and optimal method. A three-dimensional heat transfer model for OT is established using COMSOL Multiphysics to explore the OT uniformity of the Antarctic krill block. The simulated temperature profiles are successfully validated using the measured values, confirming good temperature uniformity. Moreover, the simulation revealed hot and cold spots at different positions. At the endpoint of tempering (545 s), the temperature difference between the two spots was 1.364°C using the fine-tuning method. These results are relevant to the design of novel OT systems.