Effect of boldo (Peumus boldus M.) pretreatment on kinetics of supercritical CO2 extraction of essential oil Original Research Article

This work examined the effect of the solid matrix on supercritical carbon dioxide (SC CO2) extraction of essentials oils from boldo leaves (Peumus boldus M.) subjected to rapid decompression of a CO2-impregnated sample, conventional milling, and low-temperature milling. Low-temperature conditioning prior to milling decreased heat-driven losses of volatile compounds during milling, as attested by a higher extract yield for low-temperature (10.8 g extract/kg extract-free substrate) than conventionally (9.63 g/kg) milled sample. Extract yield was even larger for the rapidly decompressed sample (11.4 g/kg). Results of SC CO2 extraction experiments carried out at 40 °C and 10 MPa were adjusted to a diffusional model using the effective diffusivity of the extract in the solid matrix (De) and a single partition of essential oils between solid substrate and SC CO2 as best-fitting parameters. A microstructural factor (FM), which was estimated as the ratio between the binary diffusion coefficient of the essential oil in SC-CO2 under extraction conditions and De, was used to characterize the effect of sample pretreatment on extraction rates. Values of FM for rapidly decompressed (202) and low-temperature milled (1740) samples were smaller than value for conventionally milled samples (2200), which revealed that the two first treatments disrupted secretory cavities in boldo leaves more effectively than the third. This was confirmed by light microscopy observations. The work included also measurements using oregano bracts (Origanum vulgare L.) as the substrate to confirm literature reports on the SC CO2 extraction of pretreated bracts and to serve as a reference to our main results with boldo leaves. Trends with oregano coincided with those of boldo.