Solubility of sinensetin and isosinensetin from cat’s whiskers (orthosiphon stamineus) leaves in ethanol-assisted supercritical carbon dioxide extraction: experimental and modeling

Abstract

In the current study, the solubility of potent bioactive compounds from cat’s whiskers (Orthosiphon stamineus), viz. sinensetin (SIN) and isosinensetin (ISO), is measured in ethanol-assisted supercritical carbon dioxide (SC-CO2). Experiments were conducted at temperature and pressure of 40–80 °C and 10–30 MPa, respectively. Three semi-empirical models of Chrastil, del Valle-Aguilera, and Gonzalez were used to correlate the compounds’ solubility in SC-CO2 + ethanol. The highest solubility of SIN and ISO was obtained at 3.945 and 2.323 mg/L, respectively, at 10 MPa and 80 °C. The solubility data revealed the direct effect of temperature, while the pressure has a dual effect of both increasing and decreasing the compounds’ solubility. This study revealed the influence of solute’s melting point, dipole moment and molecular structure on its solubility in SC-CO2 + ethanol system. Therefore, SIN has higher solubility in SC-CO2 + ethanol system due to its lower melting and dipole moment compared to its isomer, ISO. In addition, the solubility of the SIN and ISO data was satisfactorily correlated with all semi-empirical models, with less than 4.0% of the AARD%. The enthalpy of vaporization and solvation for SIN and ISO in SC-CO2 extraction were determined.