Water desorption thermodynamic properties of pineapple

The water desorption isotherms of pineapple were determined at 5, 15, 25, 35 and 45 °C by using a gravimetric technique within the water activity range of 0.1–0.9. The effect of the temperature showed a cross-over of the desorption isotherms at water activity of 0.75. The experimental data was fitted to the GAB model taking into account the effect of the temperature. The obtained simulation could be considered satisfactory (mean relative error <5.0% and percentage of explained variance >99.8%). The net isosteric heat of sorption (Qnst) and the differential entropy (Sd) were estimated as functions of the moisture content, the enthalpy–entropy compensation theory was applied to sorption isotherms and plots of Qst vs. Sd provided the isokinetic temperature, suggesting an enthalpy controlled sorption process.