Measurement of Transport Properties for The Dried Layer of Several Food Materials Undergoing Freeze-Drying

Abstract

The transport properties of several food materials have beet? presented as fundamental information to determine the drying rate freeze-drying process. As un example, the measuring method of thermal conductivity and permeability has been demonstrated for the samples of sliced and nzashed apples undergoing freeze drying. Both samples were freeze-dried at constant surface temperatures ranging from -10 to 70 under the usual pressure range of commercial operations. A mathematical model, based on quasi-steady state analysis, was formulated and then applied to the drying data to determine these transport properties for the dried layer of the sample undergoing freeze-drying. Values of thermal conductivity were found to be almost the same between sliced and mashed samples. However: the permeability data of the mashed apples were more than 4 times greater than that of sliced apples. Both temperature and pressure dependences on these transport properties were not recognized apparently, and the effect of freezing rate on transport properties were found to be critical for the mashed sample. The rate of water vapor flowing throught the dried layer. The transport properties for raw beef, minced beef, shrimp and coffee solutions were also presented indicating the effect of operation conditions as well as the structural parameters of the sample on these values.