Ultrasound-assisted deep eutectic solvent extraction versus alkaline extraction: Functional and structural properties of hazelnut proteins

This study compared conventional alkaline extraction and ultrasound-assisted deep eutectic solvent (DES–US) extraction for isolating functional proteins from hazelnut meal, an underutilized oilseed by-product. Alkaline extraction at pH 10 achieved the highest protein recovery (~260 mg/g) and extraction efficiency (~63 %), while DES–US systems yielded moderate soluble recoveries (~200–220 mg/g) but showed reduced final protein yields (~80 mg/g) due to precipitation challenges. Molecular weight profiles confirmed both methods effectively preserved major storage proteins, including 7S and 11S globulins and 2S albumins. Secondary structural analyses revealed pronounced pH-induced denaturation in alkaline extracts, versus high α-helix retention in DES–US samples (e.g., DES-GLU 95.7 %, DES-SOR 81.6 %). DES–US systems also exhibited higher solubility (~75–76 %) compared to alkaline extracts (~58–63 %). Emulsifying activity index was significantly higher for DES–US (DES-GLY ~15 m 2 /g) than alkaline (<6 m 2 /g), while emulsion stability peaked at ~60 min for DES-SOR versus ~5–6 min for alkaline samples. Conversely, alkaline extracts demonstrated superior foaming capacity (~50 % for ALK10) and stability (~40–50 % at 120 min), while DES–US foams were less stable (~10–25 % FC). In vitro digestibility was highest for DES–US isolates (DES-SOR ~76 %, DES-GLY ~75.1 %) compared to alkaline treatments (~57.6–65.3 %). These results suggest DES–US extraction offers a greener, scalable strategy for producing hazelnut proteins with improved solubility, emulsifying properties, and digestibility, supporting sustainable ingredient development from agro-industrial residues. • DES–US extraction preserved hazelnut protein structure better than alkaline extraction. • DES–US isolates showed higher solubility, emulsifying activity, and digestibility. • Alkaline extraction gave higher yields and foaming capacity. • DES–US offers a greener strategy to produce functional plant proteins.