Thermodynamic properties and water desorption isotherms of Golden Delicious apples

Moisture desorption isotherms of apples (Golden Delicious) were determined. Experimental desorption data were fitted by 13 mathematical models. The influence of temperature on desorption isotherms was more indicated at high water activities. The GAB, Halsey, Modified Halsey, Oswin, Chen, Ferro Fontan, Lewicki (1998) and Lewicki (2000) models correlated well to the experimental desorption data over the entire field of temperatures and water activities explored. In order to well understand the water properties and to evaluate the energy requirements for transport phenomena during processing, the thermodynamic properties were evaluated from the experimental desorption data. The enthalpy-entropy compensation theory was validated by the variation of net isosteric heat versus differential entropy. This variation provided the isokinetic temperature and the free energy indicating that the desorption process in apple was a non-spontaneous and enthalpy-driven mechanism.