Due to increasing demand of natural antioxidants for pharmaceutical, food and cosmetic applications, extraction of polyphenols from natural resources has received enormous attention. In this regard, ...microalgae biomass exhibits great potential for target bioactive compounds accumulation. Conventionally, petroleum-derived volatile organic solvents (VOCs) and water have been used to recover polyphenols from biomass; however, VOCs are hazardous, nonenvironmentally friendly solvents while water suffers from coextraction of other impurities. Therefore, the goal of this work is to evaluate renewable deep eutectic solvents (DES) as alternative to conventional solvents for recovering polyphenols from microalgal biomass. In particular, Chlorella vulgaris was subjected to solvent extraction using 12 DES systems composed of choline chloride (ChCl) and polyols including glycerol (Gly), ethylene glycol (EG), 1,3-propanediol (PDO) and 1,4-butanediol (BDO) and two benchmark conventional solvents, namely ethyl acetate and water. Initially, the extraction efficiency was assessed based on total phenolic content (TPC) via Folin–Ciocalteu method, as the most favorable operating conditions were determined (i.e., temperature of 60 °C, extraction time of 100 min and 20:1 solvent to biomass ratio). Afterward, solvent extracts were analyzed for their antioxidant activity via DPPH free radical scavenging method and their polyphenolic profiles were characterized via chromatographic analysis, with major phenolic compounds being gallic acid, caffeic acid, p-coumaric acid and ferulic acid. Furthermore, biomass surface characterization was performed via scanning electron microscopy (SEM) to further understand the effect of the solvents during the extraction process. Overall results support that polyol-based DES outperformed conventional solvents in terms of polyphenolic extraction efficiency, antioxidant activity of the extracts and selectivity of target antioxidants from Chlorella vulgaris, setting the grounds for developing more sustainable extraction processes for recovering natural antioxidants from microalgae biomass.
