Mathematical modelling of microwave food thawing

CAMPAÑONE LAURA A.; ZARITZKY N

Estados Unidos

Congreso; Annual Meeting and Food Expo, IFT (Institute of Food Technologists); 2006

Justification: The use of microwave thawing in the food industry decreases processing times when compared to conventional heating methods, however, problems associated to non uniform temperature distributions, caused by differences between the dielectric properties of liquid water and ice are produced. Objectives :The objectives  were:  i)to model heat transfer during food microwave thawing of large food pieces, ii)to  validate the model measuring temperature profiles inside the foods iii)to analyze  the effect of  product size, presence of a fat layer, use of power cycles and the aid of  air convection for process optimization Methods: The mathematical model was developed by solving numerically the unsteady state heat  transfer differential equation with a power source. The model was applied to large food pieces for which Lambert´s law is valid in agreement with Maxwell equations. Physical, dielectric and thermal properties varying with temperature were fitted. An implicit finite difference method was used. Experimental temperature distributions were obtained in a microwave oven (maximum power=1000W) using cubes 6 cm side of ground beef samples; this size was selected to comply with the critical value that ensures validity of  Lambert´s Law.  Results: The model was validated with experimental data from the literature and with our experimental results. A good agreement between the predicted and the measured temperatures was obtained. A fat layer in the food surface distorted temperature profiles and maximum temperatures were located in the product-fat interfase. An increase in the fat size reduced the rate of thawing. Air convection helped to diminish uneven temperature profiles and operating with power cycles contributed to decrease product temperature allowing to a more effective use of radiation.56 Significance: the model can be used to optimize industrial applications of microwave thawing, allowing to determine temperature profiles in large and heterogeneous food pieces and the effect of power cycles and air convection.