Thermodynamic approach on water vapor sorption of Curcuma longa L. flour

In this study, water vapor sorption isotherms of Curcuma longa were determined over ranges of storage (5–40 °C) and drying (40–80 °C) temperatures. From the sorption isotherms, thermodynamic parameters (net isosteric heat of sorption, differential enthalpy and entropy, and Gibbs free energy) were estimated, and the enthalpy-entropy compensation theory was evaluated. Water vapor sorption isotherms of turmeric flour were determined using the gravimetric-statistical method. The net isosteric heat of sorption, enthalpy, entropy, and Gibbs free energy were determined via the Clausius-Clapeyron equation. The GAB model showed the best fit to describe the isotherms of turmeric flour (R2adj ≥ 0.998; RMSE ≤0.0065; X2 ≤ 4.22∙10−06). The equilibrium moisture content (Xeq) of turmeric flour decreased with increasing temperature. The isotherms for all temperatures exhibited type II behavior. The isosteric heat of sorption, differential enthalpy, and entropy decreased with increasing temperature. It was possible to validate the enthalpy-entropy compensation theory, and the process was driven by enthalpy, characterizing it as non-spontaneous.