MOISTURE LOSS AS RELATED TO HEATING UNIFORMITY IN MICROWAVE PROCESSING OF SOLID FOODS

Moisture loss due to internal evaporation and its relationship to nonuniformity of heating in microwave reheating of high moisture solid foods was studied. A simple heat and mass transfer model was developed that excluded diffusional limitations of moisture movement. Microwave absorption and some dielectric and thermal properties were measured as input parameters to the model. Effect of varying microwave penetration with moisture level and temperature was included. For smaller total moisture loss, typical for a reheating application, predictions of total moisture loss and temperatures matched well with experimental data. Most of the moisture loss occurred from the edges due to higher temperature at these locations. Uniformity of heating to achieve a given average temperature is the key variable controlling total moisture loss. When starting from a frozen material, heating is much more nonuniform, leading to a greater moisture loss. As surface area increases for a given volume, uniformity of heating increases and the total moisture loss reduces. This simple model can be an effective tool in computer-aided optimization of food products and processes.