Green extraction using natural deep eutectic solvents for the recovery of proteins from sunflower meal

Sunflower meal (SM) is a promising source of plant-based protein, yet traditional alkaline extraction often leads to protein denaturation and limited functional performance. This study investigated the use of natural deep eutectic solvents (DES), specifically choline chloride:glycerol (ChCl:Gly) and choline chloride:glucose (ChCl:Glu), for the green extraction of sunflower proteins. Among ten DES formulations tested, ChCl:Glu and ChCl:Gly yielded the highest soluble protein content (12.88 and 12.34 g/100 g, respectively) using ultrasound-assisted extraction. Proteins were compared to those obtained via alkaline extraction in terms of yield, structure, solubility, digestibility, and bioaccessibility. The ChCl:Gly isolate demonstrated the highest solubility (36.20 %) and degree of hydrolysis (57.26 %), while ChCl:Glu preserved structural integrity with high β-sheet content but exhibited limited solubility (<0.50 %). Alkaline extraction led to structural disruption, protein aggregation, and reduced digestibility (50.78 %). FTIR and CD analyses revealed that DES-extracted proteins retained more β-turns and secondary structures, supported by distinct Amide I-III band preservation. Morphologically, ChCl:Gly yielded smooth, spherical particles with a favorable size (222.6 nm) and zeta potential (-22.1 mV), indicating colloidal stability. All isolates showed comparable protein bioaccessibility (∼70 %) under simulated digestion. Overall, DES-based extraction, especially with ChCl:Gly, enhanced protein functionality while preserving structure, offering a sustainable and efficient alternative to conventional methods.