Structure-functional properties and protein quality of climate-smart white lupin (Lupinus albus) protein isolates: Impact of deep eutectic solvent and conventional protein extraction methods

ABSTRACT Lupin is a promising alternative for the protein industry due to its species diversity, protein content and composition, and tolerance to climate stress. Therefore, this study aims to extract protein with high purity and functionality from lupin using a green and sustainable deep eutectic solvent (DES) system, comprising choline chloride and glycerol. Protein extraction conditions were optimized using response surface methodology, and the extracted protein was characterized for physicochemical, functional, and protein quality parameters compared to alkaline-extracted protein isolate. The observed optimum conditions for DES-based protein extraction were a solid-to-liquid ratio of 1:17.5 (w/w), a reaction time of 60 min, and a water content of 54% (w/w). Under optimal conditions, protein content, protein yield, and protein recovery rates of 88.42±0.09%, 64.47±0.56%, and 23.76±0.21%, respectively, were achieved. Alkaline extraction showed a higher protein content but lower yield and recovery ( P< 0.05). According to secondary structure analysis, α -helix (24.16%) and β -sheet (66.08%) contents in DES-extracted protein were higher than those of alkaline-extracted protein. Intermolecular β -sheets (12.51%) as protein aggregates were observed only in alkaline-extracted protein, indicating higher protein aggregation and denaturation. DES-extracted protein had similar or increased functional properties compared to alkaline-extracted protein ( P< 0.05). Moreover, remarkable gelation properties were observed with DES-extracted protein. In vitro protein digestibility (IVPD) was not significantly different ( P< 0.05) between protein isolates (90.8–91.8%). The DES-extracted protein contained a higher content of sulfur amino acids than the alkaline-extracted protein. DES protein extraction is a promising technique that could serve as an alternative to conventional alkaline extraction to produce sustainable and high-purity protein ingredients from white lupin.