Matrix effects in supercritical CO2 extraction of essential oils from plant material

In this work, we reviewed the effect of the solid matrix in the supercritical CO2 (SC-CO2) extraction of essentials oils from plant material. A diffusional model was adopted that assumed the substrate is as an homogeneous solid and the partition of essential oils between the solid substrate and the SC-CO2 phases is constant. The model was fitted to literature data from several plant materials (relevant solute identified between parenthesis): chamomile flowers (α-bisabolol), lavender flowers (camphor), oregano bracts (thymol), pennyroyal leaves and flowers (menthol), and sage leaves (1,8-cineole). Based on values of binary diffusion coefficient of the solute in the solvent (D12) from a literature correlation, and the best-fit values of effective diffusivity of the solute in the solid matrix (De) we estimated the value of the so-called microstructural factor (MF), which is defined as the ratio between D12 and De which ranged from 420 for pennyroyal to 25,000 for oregano. MF encompasses several factors, mainly related with to the microstructure of the substrate, that affect the extraction rate of a solid substrate with a solvent.