Thermodynamic Properties of Water Desorption of Papaya

Abstract

Thermodynamic properties were obtained from desorption isotherm data for papaya at 40, 50, 60 and 70C. The specific objectives were to model desorption isotherms by GAB and BET models and to apply the enthalpy-entropy compensation theory to desorption isotherm. The GAB model fitted well the data with monolayer moisture content varying from 0.086 to 0.103 g water/g solids. Equilibrium moisture content decreased with increasing temperature. The net isosteric heat of desorption was determined using Clausius–Clapeyron equation and decreased with increasing moisture content varying from 2.52 to 14.26 kJ/mol. The differential entropy values decreased with moisture content from 0.037 to 0.007 J/mol K. The enthalpy-entropy theory proved to be valid since the relationship between enthalpy and entropy was linear and the harmonic temperature (327.6 K) differed from the sample isokinetic temperature (383.4 K). Through the entropy-enthalpy theory, it could be concluded that the water desorption isotherm of papaya is a nonspontaneous process and enthalpy controlled. Practical Applications This work presents information about the moisture sorption properties of papaya fruit. Moisture sorption isotherms are important to estimate drying time, predict ingredients behavior upon mixing, select packaging, model moisture changes that occur during storage and estimate shelf life stability. In addition, moisture isotherm supplies thermodynamic properties that permit estimation of energy requirement of drying process. Because papaya is extremely perishable, dehydration could be a necessary step in the processing. Therefore, this work intends to contribute in providing useful information for designing drying process of papaya.