Ultrasound-assisted deep eutectic solvent (UDES) extraction was explored as a sustainable strategy to recover proteins from flaxseed cake, a by-product of oil production. Optimised extraction conditions (30,1 liquid-to-solid ratio, 75 °C, 60 min) resulted in a protein content of 57.78%, in comparison to conventional alkaline extraction with 43.54%. Proteomic and amino acid analyses revealed a balanced composition rich in 2S albumin (conlinins), known for their nutritional quality and potential to form bioactive peptides. UDES-modified proteins showed improved thermal stability and distinctive smooth, low-porosity morphology compared to alkaline-derived isolates. Whilst all samples exhibited similar protein bio-accessibility (approximately 60%) under simulated digestion, the proteins obtained by UDES displayed reduced emulsifying and water/oil binding capacities, suggesting limited functional potential. Thus, UDES extraction offers an environmentally friendly route for converting flaxseed cake into high-value protein ingredients, though further optimization is needed to tailor functionality for specific food applications.
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