Moisture Sorption Thermodynamics of Camellia oleifera

Moisture sorption isotherms of shelled and unshelled Camellia oleifera were determined using a gravimetric static method at 20, 30 and 40 A degrees C with water activity ranging from 0.111 to 0.976. Estimated parameters and fitting ability of seven models were evaluated, and the Peleg model provided the best description of the experimental sorption behaviour. The experimental data and the models were also used to obtain thermodynamic functions. The differential enthalpy decreased rapidly as the moisture content increased, when the moisture content exceeded 7 % (dry basis) the value of differential enthalpy tended to zero. The differential entropy showed similar trends. Spreading pressure increased with increasing water activity and decreased with increasing temperature at a given water activity. Net integral enthalpy increased slightly with moisture content to a maximum value, and thereafter decreased with increasing moisture content. However, net integral entropy decreased gradually with increasing moisture content, until reach to a minimum value and then increased slightly with further increases in moisture content.