Extraction of brewer's spent grain protein using natural deep eutectic solvent compared to alkaline extraction: Evaluating their yields, physicochemical characteristics, and functionalities

The present study compared the effectiveness of natural deep eutectic solvent (NADES) and alkaline in extracting proteins from brewer's spent grain (BSG). The extraction effectiveness was examined by the (i) yield, (ii) physicochemical characteristics (i.e., molecular weight, protein secondary structures, amino acid compositions, thermal stability), and (iii) food-relevant functionalities (i.e., water/oil holding capacities, emulsifying, foaming properties) of BSG protein extracts. Choline chloride-trehalose (3:1 mol/mol) known for its protein stabilizing effect was used as the model NADES. The ideal NADES extraction conditions to optimize the yield were first determined at 60℃, 1:15 (w/v) BSG-to-solvent ratio, and 75:25 (v/v) NADES-to-water ratio. At their respective optimal conditions, NADES extraction produced a higher yield than alkaline extraction (42 vs. 34 wt%). Minimal variations were observed between NADES and alkaline-extracted proteins in their molecular weight, protein secondary structures, amino acid profiles, and water/oil holding capacities. Nevertheless, NADES-extracted protein exhibited superior (1) thermal stability, hence reaffirming the protein stabilizing effect of NADES, and (2) emulsifying/foaming properties postulated due to their distinct amino acid compositions. The present results demonstrated NADES extraction achieved outcomes comparable to alkaline extraction in most aspects, while surpassing it in yield and proteins’ thermal stability, emulsifying/foaming properties. Future studies should focus on optimizing the yield of NADES extraction to improve its techno-economic viability.