Diethylene glycol-zinc chloride based deep eutectic solvent for green extraction of bixin compound

Abstract

Deep eutectic solvents (DESs) are ionic liquid alternatives that replace volatile and flammable organic solvents. DESs are formed by hydrogen bond interaction between the hydrogen bond donor (HBD) and the hydrogen bond acceptor (HBA). We prepared DES using zinc chloride (ZnCl₂) as HBA and diethylene glycol (DEG) as HBD. Formed DES was applied to extract the bixin contained in annatto seeds. The homogenous liquid mixtures were analysed for their pH, viscosity, density, conductivity, thermal properties, and solubility in various solvents. Bixin extracted using DES was identified by thin-layer chromatography (TLC), UV–Vis spectrophotometer, Fourier Transform Infra-Red (FTIR), and Proton Nuclear Magnetic Resonance (¹HNMR). The mixtures with a mole fraction of ZnCl₂ 0.1 (DES1), 0.2 (DES2), and 0.3 (DES3) are liquid at room temperature. The analysis results prove that bixin has been successfully extracted using DES, where DES1 was better for bixin extraction than DES2 and DES3, with extracted bixin levels of 32.42, 28.84, and 0.46 mg g^-1 by dry seeds mass, respectively. In this case, DES1, DES2, and DES3 could extract 62.17, 55.31, and 0.88 % of bixin from the entire total bixin contained in annatto seeds. The DES can be used for bixin extraction using a relatively simple method based on the results obtained.