MOISTURE DISTRIBUTION IN SPHERICAL FOODS IN MICROWAVE DRYING

Abstract

Moisture distribution in spheres of potato (Solanum tuberosum) and yam (Dioscorea japonica) tubers during microwave drying was investigated. Moisture variation at various locations within the samples was experimentally determined for different drying times. A numerical simulation model was developed based on a modified form of Lambert's law for microwave penetration in spheres and on moisture transfer in both liquid and vapor phases. This model was used to study various factors influencing moisture distribution. Moisture profile during microwave drying was strongly influenced by non-uniform microwave energy distribution within the foods. The core moisture contents were lower than other parts of potato and yam spheres of the various sizes tested in this study (2.6 cm to 6.0 cm diameter). The sphere radius to microwave penetration ratio (2αr_o) was an important parameter affecting the moisture profile in spherical foods. For 2αr_o of less than 2.0, the moisture content in the center of potato and yam spheres was markedly lower than the rest of the food, but for 2αr_o between 2.5 and 4, moisture contents at the center and close to the surface were lower than the average moisture content.