Structural and functional improvement of hazelnut protein using choline chloride–ethylene glycol

Defatted hazelnut meal (DHF) is rich in protein, yet protein extraction using conventional alkali extraction-acid precipitation methods often suffers from low purity, poor functional properties, and significant environmental concerns. In this study, choline chloride-ethylene glycol combined with ultrasound-assisted extraction was applied, and three separation strategies – dialysis, ethanol precipitation, and acid precipitation – were compared. The results showed that DES combined with dialysis (DES-DHP) yielded the highest protein purity (80.00 ± 0.95%) and demonstrated superior solubility, foam stability, and thermal stability compared to traditional methods. Fourier transform infrared (FT-IR) spectroscopy revealed that DES extraction better preserved the β-sheet structure, enhancing molecular stability; differential scanning calorimetry further confirmed its thermal stability advantage. This approach offers a promising, green, and efficient strategy for the high-value utilization of DHF.