Development and characterisation of novel terpenoid-based hydrophobic deep eutectic solvents for sustainable extraction of bioactive antioxidants from Rosmarinus officinalis L

Abstract

With the increasing demand for sustainability and green practices in industrial operations, deep eutectic solvents (DES) emerge as promising alternatives to organic solvents for the extraction of bioactive compounds. However, the inclusion of DES in industrial processes is severely limited by their hig density and viscosity as it hinders mass transfer. Additionally, low selectivity towards medium and amphiphilic bioactive compounds leads to unfavourable efficiency. This study aimed to develop, characterise, and evaluate low-density novel terpenoid-based DESs, containing fatty acid and alcohol, as effective hydrophobic extractants. The formation and stability of the newly developed DES were confirmed by validating the hydrogen bonds. The density as a function of temperature was investigated, revealing that all the developed hydrophobic DES had densities lower than water. The polarity of the solvents was assessed as it plays a vital role in the “solvation” of the bioactive compounds through Nile red assay. Although the hydrophobic DES had lower polarity than organic solvents, the screened DES showed a higher extraction yield of amphiphilic compounds of carnosic acid and carnosol, demonstrating their effectiveness. This is due to the high van der Waals interactions between the amphiphilic compounds and the alkyl chain of fatty acids and alcohols in the DES. Overall, the low density and high selectivity of the new hydrophobic DES developed in this study were found to be viable extractants for the sustainable extraction of bioactive compounds, particularly amphiphilic compounds.