Measurement and modeling of supercritical fluid extraction curves of Eucalyptus globulus bark: Influence of the operating conditions upon yields and extract composition

Eucalyptus globulus bark is an interesting source of triterpenic acids (TTAs), mainly ursolic, betulinic, oleanolic, betulonic, 3-acetylursolic, and 3-acetyloleanolic acids, which possess confirmed bioactivity. In this work, the supercritical fluid extraction of E. globulus bark has been carried out in order to measure the cumulative curves in terms of total yield, TTAs yield, free TTAs yield, acetylated TTAs yield, and TTAs concentration in the extracts. The influence of pressure, temperature, ethanol (cosolvent) content, and carbon dioxide flow rate upon the previous responses have been analyzed by performing experiments in the ranges of 120–200 bar, 40–60 °C, 0–5% EtOH, and 6 − 14  g CO 2  min − 1 . The experimental curves have been modeled with Logistic, Desorption, Simple Single Plate, and Diffusion models. In the whole, results showed that pressure and ethanol content imparted a significant effect upon extraction curves, final yields, and extract concentrations, and that external limitations to mass transfer affected some runs. The individual families of free and acetylated TTAs exhibited distinct extraction trends. Modeling allowed us to confirm not only the major role played by intraparticle diffusion upon the SFE but also the contribution of film resistance in some assays. After analyzing all results, a two-step experiment in series has been performed, making possible to enrich the TTAs content in the extract due to the distinct conditions adopted in each stage.