Simultaneous extraction with two phases (modified supercritical CO2 and CO2-expanded liquid) to enhance sustainable extraction/isolation of pinocembrin from Lippia origanoides (Verbenaceae)

Abstract

Some of the challenges to developing greener sample preparation procedures are related to finding solvents and practices with low environmental impacts. Given the importance of CO₂, water, and ethanol compared to other green solvents in flavonoid extractions, it is convenient to explore changes in how they are employed. Depending on temperature and pressure, these three solvents may present total or partial miscibility that can be used conveniently in sample preparation. In this work, the Lippia origanoides (Verbenaceae family) vegetal material remnant after essential oil distillation was extracted with either aqueous ethanol (EtOH), ethanol-modified supercritical CO₂ (EtOHCO₂), or two coexisting CO₂ fluid phases [(CO₂)²]. The latter was the extractive practice that afforded higher selectivity and yield of pinocembrin (Pn) and galangin (Gn), two important active ingredients for pharmaceutical applications. EtOH extraction was the practice with the highest whole yield, and its extract contained mainly glycosylated compounds, in contrast to those extraction systems that involved CO₂. The presence of CO₂ allowed selective extraction of nonglycosylated flavonoids, possibly due to π−π intermolecular interactions with them. Flavonoids whose B-ring is a benzene or phenol group were recovered in higher amount. By means of the EtOHCO₂ and (CO₂)² techniques, the extraction/isolation of Pn and Gn was achieved with less ethanol consumption and lower environmental impacts. The best setup was extraction with (CO₂)² and isolation by preparative HPLC. These results are promising for increasing selectivity and yield in some specific sample preparations.