Deep eutectic solvents for protein extraction: mechanisms, performance, and green metrics

<p dir="ltr">Protein extraction is a cornerstone process in biotechnology, food science, and pharmaceuticals, yet it remains constrained by reliance on volatile organic solvents that are often toxic, energy-intensive, and environmentally unsustainable. Deep eutectic solvents (DESs) are proposed as greener media for protein extraction but reported results and sustainability claims are uneven across studies. This review provides a systematic assessment of DESs for protein extraction, with emphasis on their mechanisms of action, extraction performance, and alignment with green chemistry principles. A structured literature review summarises data from various extraction methods. Reported yield, purity, and activity are compiled and considered alongside environmental factor (E-factor), process mass intensity, and available life-cycle information. The reviewed studies show that DES formulations, when appropriately hydrated and with viscosity controlled, can match or exceed conventional solvents in yield and preservation of protein function. Performance depends mainly on the choice of HBA and HBD pair, water-activity range, and salting-in and out effects; process-intensification steps reduce mass-transfer limits in dense matrices. Sustainability benefits are case dependent and are influenced by solvent make-up, recycling efficiency, and the extent of downstream purification. The review concludes with practical design rules and a reporting checklist covering composition verification, water content, recyclability, and residual-solvent limits. The main contribution is an integrated assessment that links mechanism, process performance, and quantitative sustainability metrics in one framework, enabling consistent comparison and more reliable scale-up of DES-enabled protein extraction.</p>