Water sorption thermodynamic properties applied to persimmon skin and pulp

Moisture equilibrium data of persimmon skin and pulp were determined using the static gravimetric method. Adsorption and desorption isotherms were obtained in the range of 20–70°C, to water activities (aw) from 0.02 to 0.85. The application of the GAB model to the experimental results, using direct nonlinear regression analysis, provided a good agreement between experimental and calculated values. The net isosteric heat of sorption was estimated from equilibrium sorption data, using the Clausius–Clapeyron equation. Isosteric heats of sorption were found to increase with increasing temperature and could be well adjusted by an exponential relationship. The enthalpy–entropy compensation theory was applied to sorption isotherms and plots of ΔH versus ΔS for skin and pulp provided the isokinetic temperatures, indicating an enthalpy controlled sorption process.