Effect of pelletization on supercritical CO2 extraction of rosemary antioxidants

Abstract

This work studied the effect of pelletization on the SuperCritical (SC) carbon dioxide (CO2) extraction yield of rosemary antioxidant fractions enriched in phenolic compounds. Dried rosemary leaves were depleted of essential oils by SC-CO2 extraction and a portion of the resulting pre-extracted leaves (control substrate) enriched in phenolic compounds was pelletized. A factorial experimental design (23) was carried out: control substrate and pellets were extracted at two temperatures (40 and 70 °C), and two extraction pressures (30 and 50 MPa). Pelletizing decreased the extraction yield from 4.28% to 1.33%. However, the volumetric yield (mass of recovered solute per unit time and per unit volume of extraction bed) of pellets was 34% higher than that of control substrate. Pelletization also decreased the antioxidant activity of the extracts, which was attributed to the high temperatures generated during the process. A linear correlation (R2 = 0.83) between the antioxidant activity and the dominant rosemary phenolic carnosic acid was observed. Sovová’s broken-and-intact cell model was applied to a selection of pellet and control substrate extraction curves to determine a microstructural factor (MF = De/D12) as best-fitting parameter. Resulting value of MF was 0.0003 for control substrate and 0.0027 for pellets. The simulation of the SC-CO2 extraction of pellets with twice the specific surface showed that a decrease of particle size can increase considerably the extraction rate and yield of the pellets. We propose pelletization, under certain restrictions of particle size and process temperature, as a way of improving rosemary antioxidant extraction yield.