Physicochemical and Functional Properties of Blue Lupin and White Lupin Protein Isolates

White lupin (WLPI) and blue lupin (BLPI) protein isolates were compared for their composition and functional properties. WLPI showed a higher protein yield (70.30%) than BLPI (66.47%), while BLPI had a slightly higher crude protein content (86.96%). Both isolates had similar essential amino acid profiles, with sulfur-containing amino acids valine and lysine being limiting. WLPI flour exhibited larger particle sizes (D4,3 of 29.3 μm) and a higher denaturation temperature (100 °C) than BLPI (D4,3 of 19.5 μm and 89 °C, respectively). However, BLPI demonstrated a higher surface hydrophobicity (688.13 arbitrary units) than WLPI (656.77 arbitrary units). WLPI showed superior in vitro protein digestibility (84.21%) and an oil-holding capacity (8.18 g/g). Analysis of sulfhydryl groups revealed higher free SH content in WLPI (27.22 μmol/g), while BLPI had a higher total SH (86.11 μmol/g) and disulfide bond content (29.44 μmol/g). These differences in the structural and physicochemical properties between WLPI and BLPI may significantly influence functional behavior in various food systems, potentially affecting their applications in food formulations.