A review of deep eutectic solvents for sustainable metabolite extraction: Physicochemical database, extraction efficiency, and recovery strategies

Conventional extraction solvents such as ethanol, methanol, acetone, and chloroform pose significant risks to human health and the environment due to their carcinogenicity, reproductive toxicity, and neurotoxicity. To address these concerns, green solvents have emerged as safer alternatives, aligning with Sustainable Development Goal (SDG) 3, which promotes health and well-being. This review provides an overview of deep eutectic solvents (DES) as promising green solvents, highlighting their physicochemical properties and applications. The physicochemical characteristics of DES are examined, with a particular focus on how hydroxyl (OH) group density, molar ratio of DES constituents, and alkyl chain length influence key parameters such as pH, water content, viscosity, density, and polarity. Moreover, the relationship between these physicochemical properties and the efficiency of DES in extracting bioactive metabolites, including primary (i.e., proteins, polysaccharides, amino acids) and secondary metabolites (i.e., flavonoids, phenolics, alkaloids), is critically discussed. By refining DES properties and optimizing extraction methodologies, their potential can be further expanded for applications in pharmaceuticals, food sciences, and biochemistry, paving the way for more sustainable and efficient bioactive compound extraction processes.