Pressure effect in supercritical CO₂ extraction of plant seeds

Effect of pressure on supercritical carbon dioxide extraction from various seeds was studied. Three kinds of seeds (rosehip, loquat and physic nut) were used as materials. Extraction was conducted at constant temperature (40, 60 and 80 °C), at CO₂ flow rate of 3 ml/min and at various pressures (15-9 MPa). Recovery of extract was compared with soxhlet extraction recovery using hexane as solvent. Based on results at constant temperature, the recovery of rosehip seed oil increased with increasing pressure at short extraction time, but decreased as extraction time progressed. Compared with soxhlet extraction, SC-CO₂ extraction could extract more rosehip oil higher than soxhlet extraction using hexane. In the extraction of rosehip seed oil, the cross-over region was observed. The recovery of loquat seed oil increased with decreasing pressure at 60 and 80 °C, but at 40 °C, extraction recovery was independent of the pressure. For physic nut, increasing pressure allowed high extraction recovery from 83.7 to 88.7% at constant temperature. However, the SC-CO₂ extraction could not completely extract oil from physic nut seeds compared with soxhlet extraction using hexane. The experimental results could be described using two simple models, the partitioning K_D model and a two-site kinetic model. The two-site kinetic model applied well at higher pressure compared whereas the K_D model failed to correlate the data at high pressure.