Deep eutectic solvents applied in the extraction and stabilization of rosemary (Rosmarinus officinalis L.) phenolic compounds

Most conventional organic solvents are toxic and offer high risks to human health. In this context, green solvents, such as deep eutectic solvents (DES), have been developed as a promising environmentally-friendly solvent capable of replacing organic ones, mainly in the extraction and purification of biomolecules. In this study, four choline chloride-based deep eutectic solvents were used in ultrasound-assisted extraction of phenolic content from Rosmarinus officinalis L. The solvents were glycerol:choline chloride (1:2 v/w) and water (10% w/w) - CGH; lactic acid:choline chloride (1:3 v/w) and water (10% w/w) - CALH; 1,2-propanediol:choline chloride (1:2 v/w) and water (10% w/w) - CPH; and oxalic acid:choline chloride (1:1 v/w) and water (10% w/w) CAOH. Pure ethanol was used for comparison. The antioxidant capacity, as well as the kinetic degradation, were evaluated for each of the extracts obtained. Although the extract obtained with CGH had the lowest value of total phenolic compounds (TCP), all DES-based extracts presented higher antioxidant capacity than the alcohol extract (DPPH and FRAP assays). In addition, the kinetic degradation assay demonstrated that the ethanol extract had the lowest stabilization capacity of the phenolic compounds present in the extract. The kinetic degradation of phenolic compounds was well described by the Weibull model for all extracts evaluated. Therefore, it has been possible to show that chloride-based deep eutectic solvents can be used as green solvents to substitute for organic solvents, mainly in the extraction and stabilization of phenolic compounds from Rosmarinus officinalis L.