Helena Abramovič and Cveto Klofutar
Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia

The water sorption isotherms of some maltodextrins with dextrose equivalent values ranging from 5 to 25 were determined using an isopiestic method in the range of water activity between 0.1 to 0.98 and at a temperature of 298 K. The Guggenheim - Anderson - de Boer model (GAB), the Brunauer - Emmett - Teller model (BET) and the Caurie model were tested to fit the experimental data. Equations of the GAB type and Caurie model  fit the experimental data well between aw = 0.1 to 0.9, while the BET equation fits only up to aw = 0.6. The water content adsorbed in the monomolecular layers was evaluated. The constants related to the heat of sorption for the first and subsequent layers of molecules and to the heat of condensation of pure water were estimated. On the basis of the Caurie model the number of monolayers of water adsorbed and the area of one gram of adsorbent which contains only water molecules in the monolayer were calculated.