Extraction of boldo (Peumus boldus M.) leaves with supercritical CO2 and hot pressurized water

High-activity fractions in boldo leaves were extracted with supercritical CO2 (SC-CO2) and hot pressurized water (HPW). Total yield after 3 h of extraction (0.6-3.5%) in low-pressure SC-CO2 experiments increased with process pressure (60-150 bar) and decreased with temperature (30-60 °C), as expected. The extract obtained with SC-CO2 at 50 °C and 90 bar contained approximately 50% of essential oil components. In higher pressure experiments with solvent mixtures, the yield increased with pressure (300-450 bar) and modifier concentration (2-10% ethanol), ranging 0.14-1.95 ppm for the alkaloid boldine and 1.8-4.8% for total solids following 1.5 h treatment at 50 °C. Boldine recovery was solubility-controlled, reaching 7.4 ppm after 7-h extraction at 450 bar and 50 °C using an ethanol-SC-CO2 mixture (5% co-solvent). Boldine solubility and yield decreased when using pure CO2 at higher pressure (600 bar, 50 °C). The extract yield after 3 h batch-wise HPW extraction increased from 36.9% at 100 °C to 53.2% at 125 °C, and then decreased as temperature was increased to 175 °C. Boldine yield decreased from 26.8 ppm at 100 °C to 0.7 ppm at 125 °C, and was negligible at ⩾150 °C. The essential oil yield increased to a maximum at 110 °C and was negligible at ⩾150 °C also. The ranking of antioxidant potency of various extracts was as follows: HPW at 110 °C > methanol (soxhlet extraction) ≫ high-pressure SC-CO2 with or without polar co-solvent > low-pressure SC-CO2.