Estimation of Dielectric Properties of Food Materials During Microwave Tempering and Heating

The present study concerns the estimation of the dielectric properties of both frozen and defrosted materials during a microwave tempering and heating process. A continuous wave at 2.45 GHz is fed into a rectangular waveguide and the sample, made of methylcellulose gel, fills the whole cross-section of the guide. Temperatures are detected within both frozen and defrosted samples during the heating treatment. The experimental temperatures are compared to the results obtained with a 2D finite element model, using the COMSOLA (R) 4.2 software. The dielectric properties of the sample are estimated from the local temperature changes during the microwave tempering. For the defrosted zone, the estimation is compared to dielectric properties measurements with the open-ended coaxial probe. The results show good correspondence between experimental and simulated data. The uncertainties of the estimated permittivity and loss factors are also evaluated with a good accuracy for the frozen and defrosted phases. The estimation procedure is thus a promising tool in order to avoid complex experimental measurements of dielectric properties.