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 obt ained in the range of 20-70 degrees C, to water activities (a(w)) from 0.02 to 0.85. The application of the GAB model to the experimental results, usi ng 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 equa tion. Isosteric heats of sorption were found to increase with increasing te mperature and could be well adjusted by an exponential relationship. The en thalpy-entropy compensation theory was applied to sorption isotherms and pl ots of Delta H versus Delta S for skin and pulp provided the isokinetic tem peratures, indicating an enthalpy controlled sorption process. (C) 2000 Els evier Science B.V. All rights reserved.