Supercritical CO2 extraction of pinocembrin from Lippia origanoides distillation residues. 1. Multicomponent solubility and equilibrium partition

Abstract

Steam-distilled oregano (Lippia origanoides) distillation process was analyzed and described as a model binary mixture. The most abundant identified and selected compounds were pinocembrin, a high-value flavonoid, as representative of the minor fraction, and octacosane, a cuticular wax, of the major fraction. Thermodynamic solubility of the solid multicomponent mixture in supercritical CO2 was measured at 313 K and 323 K, and pressures from 8.6 to 32.1 MPa, using a dynamic-analytical method with on-line HPLC analysis. The molar fraction of pinocembrin in CO2-rich phase was assessed from 4.8.10(-6) to 33.10(-6) mol/mol. The solid + fluid equilibrium for the ternary model system was modeled with the Peng-Robinson equation of state and the classical van der Waals mixing rules. Extraction experiments of the solid multicomponent mixture with supercritical CO2 modified with 2-9% w/w ethanol, were carried out in a one-pass pilot scale apparatus at 308 K, 323 K and 338 K, and pressures of 18 MPa, 26 MPa, and 34 MPa. For each sample, the pinocembrin content was assessed. The extraction curves for oleoresin and pinocembrin were represented with empirical models from which the oleoresin partition constants were estimated, that were in range from 0.03 to 0.13 kg/kg substrate/CO2 depending on extraction conditions. However, the partition constant remained virtually invariant, independently of changes in the extraction temperature and pressure conditions, and the ethanol content in CO2, with an average value of 0.08 kg/kg substrate/CO2. These results will facilitate using a simplified mass transfer model to describe oleoresin extraction from steam-distilled L. origanoides.