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 that 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 m²/g) than alkaline (<6 m²/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.