Particle size effects on supercritical CO2 extraction of oil‐containing seeds

Rosehip seeds were milled, sieved, and extracted with 26.3 g/g substrate/h of supercritical carbon dioxide (CO2) at 40°C and 300 bar. The extraction kinetics were characterized by an initial solubility‐controlled period (8.78 g oil/kg CO2 at 40°C and 300 bar), followed by a transition period to a final mass transfer‐controlled process. The integral yield of oil approached an asymptotic value that was dependent on the particle size of the substrate: 57.1 g oil/kg dry oil‐free substrate (large particles), 171.0 g/kg (medium‐size particles), or 391.5 g/kg (small particles). Based on gravimetric determinations and microscopic analysis, our size‐classification process segregated seed parts having different oil contents. Particles ≥0.85 mm were mainly composed of tough, lignified testa fragments devoid of oil, whereas particles ≤0.425 mm contained mostly brittle, oil‐rich germ fragments. The segregation of seed in fractions with different oil contents may be a common occurrence in supercritical extraction experiments, especially for seeds with thick and/or hard testa and small germ, whose fractions can be separated by sieving.