High-Quality Thawing of Frozen Food by Far-Infrared Radiation

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(1) ExperimentFrozen tuna was used as a sample. The sample was placed in a constant temperature box, in which fans were set inside to control an air flow rate, and was heated by a ceramic heater placed above the box. The temperature distribution was measured by using thermocouples and was recorded on a floppy disk.(2) Mathematical modelAn apparent specific heat model was introduced to predict two dimensional and three dimensional heat transfer in frozen food. A finite element method was applied to solve the fundamental equation and boundary conditions. Thermal properties (apparent specific heat, density, thermal conductivity) were estimated by Hakawa's empirical equations.(3) Experimental and numerical calculation resultsWe performed some numerical calculations to examine the influence of the heater temperature, the ambient temperature of the sample and the sample thickness on thawing rate. Experiments were carried out to check the validity of the mathematical model. Temperature distributions in samples were measured by using thermocouples and they agreed well with the theoretical predictions.During these experiments, deterioration, which was caused by drip loss or discoloration of the red muscles of tuna, was occurred because the surface temperature of the sample increased to unacceptable levels. However, we demonstrated that frozen tuna could be thawed without drip loss and discoloration by keeping the surface temperature below 10ﾟC.This was performed by irradiation of the energy intermittently or by reducing the heater temperature when the surface temperature reached 7ﾟC.