Dr. Frederick Lia and Karen Attard

Deep eutectic solvents (DES) and natural DES (NADES) have emerged as sustainable alternatives to conventional organic solvents for the extraction of bioactive compounds from olive mill waste (OMW). These systems are formed through strong hydrogen-bond interactions between a hydrogen-bond acceptor (HBA) and donor (HBD), resulting in liquids with significantly reduced melting points and highly tunable physicochemical properties, including polarity, viscosity, and solvation capacity [1]. This tunability enables the design of task-specific solvents for selective extraction of phenolics, flavonoids, and other valuable compounds.

Figure 1: Deep eutectic and natural deep eutectic solvents mechanisms.

DES/NADES enhance extraction efficiency through synergistic intermolecular interactions (hydrogen bonding, van der Waals forces, and hydrophobic effects), often outperforming conventional solvents in both yield and selectivity [2]. Their performance is further improved when combined with advanced techniques such as ultrasound-assisted extraction, microwave-assisted extraction, and dispersive liquid–liquid microextraction, which enhance mass transfer, reduce extraction time, and lower energy and solvent consumption [3,1].

In OMW valorisation, DES/NADES systems have demonstrated substantial improvements in recovery (up to 30-fold increases) and reduced processing temperatures, supporting process intensification and circular bioeconomy strategies [4]. Additionally, their low toxicity, negligible vapour pressure, and reduced environmental impact align with green analytical chemistry principles [5].
 

However, challenges including high viscosity, water sensitivity, solvent recovery limitations, and scale-up constraints remain key barriers to industrial implementation.

Funding

Funding Project ‘A Complete Sustainable Route For The Utilization Of Olive Pomance: 
Production Of Bioactive Spurt Inhibtors And Alternative Proteins - SustainOlive’ financed by Xjenza Malta-TÜBİTAK Joint Call for R&I Proposals, 2024 Call. 

References

1. Li, G. & Row, K.H., 2019. Utilization of deep eutectic solvents in dispersive liquid –liquid microextraction. Trends in Analytical Chemistry, 120, 115651. https://doi.org/10.1016/j.trac.2019.115651
2. Elicit (systematic review team), 2024. Enhancing Bioactive Extraction with NADES – Report. Mechanistic synthesis across 25 studies; H-bond networks, supramolecular assembly, and comparative performance versus conventional solvents).
3. Lanjekar, K.J. & Rathod, V.K., 2021. Application of ultrasound and natural deep eutectic solvent for the extraction of glycyrrhizic acid from Glycyrrhiza glabra: Optimization and kinetic evaluation. 
Industrial & Engineering Chemistry Research, 60(26), pp.9532–9538. https://doi.org/10.1021/acs.iecr.1c00862.
4. Fernández-Prior, M.A., Charfi, A., Bermúdez-Oria, A., Rodríguez-Juan, E., Fernández-Bolaños, J. and Rodríguez-Gutiérrez, G., 2020. Deep eutectic solvents improve the biorefinery of alperujo by extraction of bioactive molecules in combination with industrial thermal treatments. Food and Bioproducts Processing, 121, pp.131–142. https://doi.org/10.1016/j.fbp.2020.02.001

5. Coscarella, M., Nardi, M., Alipieva, K., Bonacci, S., Popova, M., Procopio, A., Scarpelli, R. & Simeonov, S., 2024. Alternative assisted extraction methods of phenolic compounds using NaDESs. Antioxidants, 13(1), 62. https://doi.org/10.3390/antiox13010062