Effect of choline chloride-oxalic acid based deep eutectic solvent on the ultrasonic assisted extraction of polyphenols from Aegle marmelos

In spite of their superior dissolution capacity for bioactive compounds, reduced environmental impact and low toxicity, the high viscosity of DES may affect the extraction capacity and efficiency, for which, necessary modification may be necessary. However, such changes can lead to a drastic reduction in the extraction yield because of the highly sensitive nature of the supramolecular structure of DES. To investigate the effect of molar ratio, water addition and temperature, ultrasound-assisted extraction of phenolic compounds from Aegle marmelos was performed with a series of DESs based on choline chloride and oxalic acid (DES: oxaline) with different molar ratio and water addition levels. HPLC-DAD was applied to quantify individual phenolic compounds. To understand the structural and physical characteristics under different processing conditions, FTIR, density and rheology analysis of oxaline were performed. Binary aqueous solvent mixtures were used as the reference. According to the experimental results, oxaline11 with 25% water and 80 °C was the best combination for extracting polyphenols from bael. The optimized condition enabled better cavitiational process by lowering viscosity and forming a stronger H-bonding between the DES and components, enhancing the extraction yield and capacity by >60% compared to conventional solvents. The results of this study highlight the potential application of deep eutectic solvent as an alternative to conventional organic solvents in food, cosmetic and pharmaceutical applications.