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

Abstract

Rosehip seeds were milled, sieved, and extracted with 26.3 g/g substrate/h of supercritical carbon dioxide (CO2) at 40degreesC and 300 bar. The extraction kinetics were characterized by an initial solubility-control led period (8.78 g oil/kg CO2 at 40degreesC 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 greater than or equal to0.85 mm were mainly composed of tough, lignified testa fragments devoid of oil, whereas particles less than or equal to0.425 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.