Lupin Species and Protein Fraction Type Affect the Conformational State and Functional Performance of the Proteins

ABSTRACT This study investigated the effects of lupin species, pH, and protein concentration on the structural and functional properties of albumin, globulin, and glutelin protein fractions isolated from white ( Lupinus albus ) and blue ( Lupinus angustifolius ) lupin seeds. The globulin and glutelin fractions exhibited characteristic pH‐dependent U‐shaped solubility curves, with minimum solubility near pH 5. Amino acid analysis revealed that white lupin globulin (WLGlo) was the only fraction not limited in sulfur‐containing amino acids (methionine + cysteine: 107% amino acid score). Blue lupin glutelin (BLGlu) demonstrated high surface hydrophobicity (3924.1), in vitro protein digestibility (92.44%), and the highest intrinsic fluorescence intensity at pH 3, indicating a conserved but enzyme‐accessible protein conformation. Far‐UV circular dichroism analysis revealed that white lupin albumin (WLAlb) possessed the highest α‐helix content at pH 7 (23%) and pH 9 (18%), reflecting a more flexible conformation. Emulsions stabilized by WLGlo at pH 3, 7, and 9 had smaller oil droplet sizes (~4–7 μm) than most of the other protein fractions. All fractions displayed excellent foaming properties, with stability exceeding 85%, and glutelin fractions showing particularly good (50%–60%) foaming capacity at pH 5. These findings establish clear structure–function relationships and demonstrate the potential of lupin protein fractions as high‐performance ingredients for diverse food applications, with each fraction offering specific advantages based on nutritional quality, structural characteristics, and functional properties.