Moisture sorption isotherm and thermodynamic properties of Centella asiatica L. (CAL) powder

Abstract

Centella asiatica L. (CAL) powder contains many medicinal properties that could be subjected to rapid deterioration due to presence of water. Moisture sorption isotherm has been widely used to predict shelf-life and storage stability as well as understanding the sorption mechanism between a material and water molecules. Aims of this study were to analyze the moisture sorption isotherm of CAL powder and its thermodynamic properties (net isosteric heat of sorption, differential entropy, and enthalpy-entropy compensation theory). A study was conducted at three different temperatures (30, 40, and 50 °C) with a range of water activities (0.06–0.92) using static gravimetric method. Results showed that CAL powder demonstrated Type-III moisture sorption isotherm behavior. Peleg isotherms relationship was found to be the most suitable model to describe the sorption isotherm curves followed by BET and Halsey. Furthermore, the net isosteric heat of sorption was determined using Peleg’s sorption isotherm model and the results showed exponentially increased as the equilibrium moisture content decreased. Enthalpy-entropy compensation theory was satisfied based on a linear relationship between differential enthalpy and entropy data obtained. Ccompensation theory also indicated that the process is an enthalpy-driven and undergoes a non-spontaneous reaction.