Phase behavior of phytosterols and cholesterol in carbon dioxide-expanded ethanol- December 2011
F Temelli, A Córdoba, E Elizondo, M Cano-Sarabia, J Veciana, and N Ventosa – The Journal of Supercritical Fluids, 2011
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 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. … In an effort to follow the changes in phase behavior a small high pressure spectroscopic cell (1 cm path length, model 5017-spq, Custom Sensors & Technology, Fenton, MO, USA) coupledto a UV-Vis spectrophotometer (UV-Visible Stellarnet CCD-array, model EPPC2000 C).
Figure 4. Change in optical density of a “phytosterol-ethanol-CO2” mixture, Ci=1.79 × 10−3 mol/mol at 25 °C and 10 MPa, with different amounts of pure ethanol addition over the mixture (decreasing XCO2), following L6 (Fig. 3). Two phase region (L + S) from XCO2 = 0.57 until 0.52. Optical density drops at XCO2 = 0.51 (Vanishing point to a single liquid phase (L)).
