Green compressed fluid technologies for downstream processing of Scenedesmus obliquus in a biorefinery approach

The fractionation of algae biomass in several high-value compounds that can be used as ingredients in other applications sets the basis of the algae biorefinery approach. The present study aimed at the extraction and fractionation of bioactive compounds from the microalga Scenedesmus obliquus, by means of applying a sequential process without the manipulation of the biomass in the extraction cell. This integrated platform of compressed fluid extraction technologies of low-environmental impact was designed in order to produce increases of solvent polarity using non-toxic solvents. The process involved the following steps:(1) supercritical fluid extraction (SFE) using supercritical carbon dioxide (ScCO₂); (2) gas expanded liquids (GXL) using 75% ethanol and 25% ScCO₂ (v/v) and; (3) pressurized liquid extraction (PLE) using water. Extraction conditions were optimized using response surface methodology (RSM) and kinetic studies. Extraction yield, antioxidant activity as well as contents of total phenols, carotenoids, proteins and sugars were the studied response variables. High performance liquid chromatography coupled to evaporative light-scattering detector (HPLC-ELSD) analyses of the fractions revealed that triacylglycerols were mainly extracted by SFE. Lutein and β-carotene were the main pigments identified in the extracts by HPLC coupled to diode array and mass spectrometry detectors (HPLC-DAD-MS/MS), which were preferentially extracted in the GXL step. Polar compounds such as proteins and sugars remained predominantly in the residue. Therefore, the green downstream platform developed in this study for valorization of the microalgae biomass, is able to produce different fractions with potential application in the food, pharmaceutical and cosmetic industries.