Characterization of citric acid monohydrate-glycerol based deep eutectic solvents which could be used as an extraction medium for hydrophilic bioactive components

Organic acids are often used as an extraction media to separate bioactive compounds in animal or plant sources. However, organic acids have a big drawback on extraction efficiency such as low yields and harmful to environment. In this study, different molar ratios of citric acid monohydrate (CAM)-glycerol (GLY) based deep eutectic solvents (DESs) were successfully produced as a new extraction media with different physicochemical characteristics. All the synthesized DESs were observed as a clear, homogenous liquid and remained stable as liquids at room temperature throughout the time. FTIR analysis confirmed the hydrogen bond and electrostatic interactions within the produced DESs as the wavenumbers of OH stretching and C = O bond in DESs were shifted. CAM-GLY 1:1 meet the lowest eutectic point compared to other ratios. The increases in molar ratio of citric acid monohydrate had produced DES with higher density and viscosity. The result showed that CAM-GLY 1:1 exhibited the lowest water absorption rate among others. The synthesized DESs also considered hydrophilic and highly soluble in a highly polar solvent as well as semi-polar solvents. To compare the extraction capacity of the extracted DES and conventional citric acid, extraction of polysaccharide from Micromelum minutum leaves was performed. Result showed that the extraction yield using the DES were in the range of 5.85 - 10.39% (w/w, dry basis). On the other hand, the yield obtained using conventional citric acid was 5.49 % (w/w, dry basis). Therefore, the DES at selected ratio has the potential in extracting natural polar and hydrophilic bioactive components, such as polysaccharides.

Automated summary

In this study, deep eutectic solvents (DESs) based on citric acid monohydrate (CAM) and glycerol (GLY) were successfully synthesized. The DES with a molar ratio of CAM-GLY 1:1 exhibited the lowest eutectic point and water absorption rate. Furthermore, the DES showed a higher extraction capacity for polysaccharides compared to conventional citric acid.