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The adsorption and desorption equilibrium moisture contents (EMC) were determined for Estameran date fruit using saturated salt solution method at 40, 50, 60 and 70°C over the range of relative humidity from 0.05 to 0.85. Equilibrium moisture content decreased with increasing the temperature from 40 to 50°C, at water activities (aw) below 0.3, while for higher water activities, crossing phenomena of the isotherm curves was detected as the temperature increased. Furthermore, equilibrium moisture content increased due to the dissolution of crystalline sugars at higher temperatures and moisture contents. The same phenomenon took place at water activity equal to 0.05 at 60 and 70°C temperatures. GAB, modified Halsey, modified Chung-Pfost, modified Oswin, modified smith and modified Henderson models were used to fit the experimental data. The GAB model was found to be the most suitable for describing the adsorption and desorption curves. The monolayer moisture content (Mm) values at different temperatures were calculated using the GAB equation. Results showed that Mm decreased with increasing temperature. The isosteric heats of desorption and adsorption of water were determined from the equilibrium data at different temperatures by Clausius-Clapyron equation. The isosteric heats of desorption and adsorption decreased with increasing water activity.

Keywords: Equilibrium moisture content, Saturation salt, Water activity, Modeling, Crossing phenomenon

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