! Evaluation!the!Use!of!Deep!Eutectic!Solvents!for!the! Extraction!of!Phenolic!Compounds:!Critical!Analysis! and!Green!Metric!Assessment

Abstract

The application of deep eutectic solvents (DESs) in the extraction of natural compounds such as phenolic compounds biomass has a great potential in small and industrial scale extraction. This may provide an environmentally, economically and cost-effective alternative option to toxic organic solvents. Despite the extensive research on the usage of DESs in natural product extraction, detailed knowledge of the effect of the physicochemical properties of DESs and target compounds on extraction efficiency still lacking. Consequently, this project aims to review and critically analysed data from different research works that utilised DESs for the extraction of phenolic compounds from various biomasses. The data analysis reveals that there is a direct correlation between the DESs polarity, viscosity and their chemical structure with the ability to extract phenolic compounds. Acid and alcohol based DESs showed relatively higher capacity to extract major phenolic compounds such as tyrosol, hydroxytyrosol, oleacein and oleocanthal. In addition, phenolic compounds pKa and molecular weight played a main role in controlling the extraction reaction efficiency. In the second part of the project, a critical assessment of the extraction method proposed by Odeh using green metrics and the 12 Principles of Green Chemistry was performed. The data was analysed and compared to two other methods used conventional and novel alternative extraction techniques. The three methods were also assessed based on reaction conditions and energy costs. Overall, it was found that using DESs is more efficient than conventional solvent in extracting natural products. In addition, DESs combined with extraction assisted techniques such as High hydrostatic pressure-assisted extraction (HHPAE) showed superior green metrics compared to Odeh’s method. However, further investigations are needed to improve the capital cost, energy cost and recycling of the DESs to make them more accessible to be implemented at industrial scale.