Phase behavior of phytosterols and cholesterol in carbon dioxide-expanded ethanol

Phytosterols have been receiving increasing attention due to their demonstrated health benefits. Micronization of phytosterol particles is desirable to enhance their physiological efficacy. To take advantage of compressed fluid-based technologies for micronization, solubility information is needed. Therefore, the objective of this study was to investigate the phase behavior of phytosterols in CO2-expanded ethanol at temperatures of 25 °C and 35 °C and 10 MPa and compare it to that of cholesterol. A high pressure system equipped with a variable volume cell was used to establish the phase behavior based on the “vanishing point” technique. A UV/Vis spectrophotometer was also used to follow the phase transitions in addition to visual observations. CO2 acted as a co-solvent at concentrations of up to ∼0.8 mole fraction. The solubility of phytosterols in CO2-expanded ethanol increased with temperature. At 35 °C, phytosterol solubility was lower than that for cholesterol, mainly due to their larger molecular weight and the presence of hydrophobic side groups in their structure. The Wubbolts model described the experimental data well. Findings of the study provide the basis for process development for micronization of phytosterols using CO2-expanded ethanol.