Supercritical carbon dioxide extraction of red pepper (Capsicum annuum L.) oleoresin

The extraction kinetics of red pepper oleoresin with supercritical carbon dioxide (SC-CO2) at 40 degreesC from a pelletized substrate was evaluated as a function of crushed-pellet particle size (D-p = 0.273-3.90 mm), superficial solvent velocity (U-s = 0.57-1.25 mm/s), and extraction pressure (320-540 bar). Batch productivity increased with substrate pelletization, which caused a 4-time increase in apparent density. Microscopy was utilized to characterize the microstructure of the pelletized substrate. Fractal analysis of binary images and mercury porosimetry allowed an estimation of pellet porosity and tortuosity, which in turn allowed an independent estimation of effective diffusivity. Solute partition between the solid matrix and SC-CO2 (K) was estimated from the initial slope of cumulative plots of oleoresin yield versus specific solvent mass, and did not depend on D-p and U-s. Yield of oleoresins and carotenoid pigments increased, and K decreased as the extraction pressure increased. A linear driving force approximation was used to model experimental data, and discrepancies between model predictions and experimental data points with large particles were explained. (C) 2003 Elsevier Ltd. All rights reserved.