Advances and challenges in the selective extraction of low molecular weight carbohydrates using ionic liquids and deep eutectic solvents

Low molecular weight carbohydrates (LMWCs) are usually found in Nature as part of complex mixtures with proteins, lipids, amino acids, etc. or other carbohydrates with different degrees of polymerization, monomeric units or glycosidic bonds. Selective extraction or fractionation processes are then required to enable their analytical characterization and the measurement of their bioactivity. In these processes, the use of the extraction solvent plays a key role and although water is the most commonly used, poor selectivity is achieved. Recently, the use of novel, environmentally friendly and tunable solvents, such as ionic liquids (ILs) and deep eutectic solvents (DESs), has been explored for the selective solubilization and extraction of LMWCs. In this review, properties and parameters of ILs and DESs affecting LMWC solvation have been discussed, while recent applications of these solvents for the selective extraction of LMWC has been reviewed. Novel approaches based on the use of ILs as solution-out agents or on the combination of DESs with advanced extraction techniques, such as microwave-assisted extraction, to obtain faster and more efficient carbohydrate extraction processes are also reported.