Supercritical fluid (CO2+ethanol) extraction of chlorophylls and carotenoids from Chlorella sorokiniana: COSMO-SAC assisted prediction of properties and experimental approach

Abstract

In this work, COSMO-SAC was used to calculate infinite dilution activity coefficients (γ∞) of carotenoids in CO2+ethanol mixtures as a theoretical approach to evaluate the effect of solvent composition on solute solubility. In an experimental approach, a central composite design was employed to evaluate the use of supercritical mixtures of CO2+ethanol to extract chlorophylls and carotenoids from the microalga Chlorella sorokiniana. The carotenoid profiles of extracts were fully evaluated, and the optimal conditions for the extraction of chlorophyll a, chlorophyll b, carotenes, lutein, zeaxanthin and violaxanthin were differentiated. Extraction temperature, pressure and the composition of the solvent proved to be relevant factors, as the experimental conditions rendered fundamentally different extraction results. The presence of ethanol proved to be essential for the efficient extraction of chlorophylls and to substantially improve the recovery of carotenoids. Scanning electron microscopy (SEM) was used to evaluate cell integrity, and indicated that the increase of pressure may have positively affected the extraction of compounds by causing disruption of the particles. The theoretical approach in this work was able to corroborate experimental results for the extraction of carotenoids from C. sorokiniana, reinforcing the hypothesis that carotenoids are extracted from the microalgal biomass as aggregates, and showing that COSMO-SAC is an important tool for the selection of the supercritical solvent.