Equilibrium moisture content and heat of sorption of longan (Dimocarpus longan Lour.)

The equilibrium moisture contents of longan were determined experimentally using the dynamic method at temperatures ranging from 30 to 50 degrees C and water activity ranging from 11 to 97%. The sorption isotherm curves of longan were sigmoidal in shape and decreased with increased temperature at constant relative humidity. Five selected isotherm models were tested to fit the experimental isotherm data of longan. The GAB model fitted the best to the experimental data of longan and the modified Oswin model was the next to the GAB model. The agreement between the best-fitted models and experimental data was excellent. The isosteric heats of sorption, determined from equilibrium data using the Clausius-Clapeyron equation, were found to be a function of moisture content.