Moisture sorption isotherms and thermodynamic properties of tow mints: Mentha pulegium and Mentha rotundifolia

Abstract

Moisture sorption isotherms of Mentha pulegium and Mentha rotundifolia were determined at 30, 40 and 50 °C using the static gravimetric method. GAB, modified Halsey and Peleg models were fitted to the experimental data and the agreement between experimental and predicted values was satisfactory. Calculation of the thermodynamic properties was further used to provide an understanding of the properties of water and energy requirements associated with the sorption behaviour. Isosteric heats of sorption were calculated through direct use of moisture isotherms by applying the Clausius-Clapeyron equation. The differential enthalpy and entropy decreased with increasing moisture content and were adequately characterized by a power law equation. A plot of differential heat versus entropy satisfied the enthalpy-entropy compensation theory.