EFFECTIVE MOISTURE DIFFUSIVITY IN POROUS MATERIALS AS A FUNCTION OF TEMPERATURE AND MOISTURE-CONTENT

Regular regime theory was used to evaluate the effective moisture diffusivity of a commercial white bread, plain sheet muffin, and baking powder biscuit as a function of moisture content based on desorption experiments. Volume shrinkage during drying was also monitored. The existence of regular regime periods in desorption processes for porous baked products was experimentally verified. Effective moisture diffusivity at temperatures between 20 and 100°C ranged from 2.5×10−5 to 5.5×10−3 cm2/s in the moisture range of 0.1–0.7 g of H20/g of solid for bread, 9.35×10−6 to 9.7×10−4 cm2/s in the moisture range of 0.1–0.65 g of H20/g of solid for biscuit, and 8.4×10−6 to 1.54×10−3 cm2/s in the moisture range of 0.1–0.9 g of H20/g of solid for muffin. The effect of temperature on effective moisture diffusivity was adequately modeled by the Arrhenius relationship. Activation energies for bread, biscuit, and muffin were found to be independent of moisture content and were 51, 51, and 55 kJ/mol, respectively. Mathematical models to relate the effective moisture diffusivity to temperature and moisture content were developed. Copyright © 1990 American Institute of Chemical Engineers (AIChE)