Development of hydrophobic eutectic solvents composed of DL-menthol and fatty acids/alcohols: Application in the extraction of capsaicinoids and carotenoids from Capsicum frutescens

Abstract

The aim of this work was to evaluate the use of DL-menthol as a eutectic solvent (ES) forming component with fatty acids (C₈ to C₁₈ acids) and alcohols fatty (C₈OH to C₁₂OH) and to identify the differences arising from the chirality between the racemic (DL-menthol) and the pure isomer (L-menthol). Moreover, the extraction of metabolite compounds from Capsicum frutescens using dried and water-saturated solvent was also investigated. The results obtained from the solid–liquid phase equilibria (SLE) diagrams showed the same eutectic point (0.2 M fraction for menthol) for both isomers. However, in both diagrams (melting and crystallization temperature) the DL-menthol-based ES exhibited a different solids line than the pure isomer at different temperatures, probably due to the D-isomer in the racemic mixture. The water content for DL-menthol: acids or fatty alcohols was very low, showing a range of 404–1067 ppm for the dried ones. For those water-saturated, values between 17,316 and 29,181 ppm were observed. Thermo-physical properties can provide important insights into intermolecular interactions and the ES structure. The density and viscosity values for these hydrophobic solvents were lower than most hydrophilic analogue solvents. Finally, these hydrophobic ES were applied to the extraction of carotenoids and capsaicinoids. The extraction efficiency values for carotenoids were higher than those for capsaicin due to the higher hydrophobicity of this compound. Furthermore, higher extraction values were also observed for water-saturated ES.