Moisture sorption thermodynamics of defatted sesame meal (DSM) Original Research Article

Determination of thermodynamic functions is essential for the analysis of theoretical energy requirements during heat and mass transfer processes such as drying and freezing. Experimental measurements of equilibrium relative humidity (ERH) and equilibrium moisture content (EMC) were used to find the best moisture sorption isotherm model for defatted sesame meal (DSM). The modified Halsey model was found to be the best fit to the experimental data. The model was used to obtain thermodynamic functions that included latent heat of sorption, differential enthalpy and entropy, monolayer moisture content, spreading pressure, net integral enthalpy and entropy. Latent heat of sorption decreased as moisture content increased before it reached an asymptote close to 30% moisture content (dry basis, d.b.). Differential enthalpy and entropy were both found to decrease exponentially with increase in moisture content. Monolayer moisture content decreased linearly with temperature. Net integral enthalpy decreased steeply with increase in moisture content up to 18% d.b. moisture content before it leveled off. Net integral entropy decreased to a minimum value at around 6.4% d.b. moisture content, increased again up to 18% d.b. moisture content, and then became constant thereafter.