Comparative study of the interaction between β-lactoglobulin and three carotenoids

Carotenoids offer numerous health benefits and exhibit strong binding affinity with β-lactoglobulin (β-lg), a major dairy protein with hydrophobic ligand-binding domains. This study examined the interaction between β-lg and three carotenoids of differing polarity: lycopene (LYC), β-carotene (β-CA), and lutein (LU). A progressive quenching of β-lg fluorescence occurred as the carotenoids concentration was raised. The quenching mechanism was static, and binding was spontaneous (Gibbs free energy, ΔG < 0). LU showed the strongest binding with β-lg. β-CA and LYC mainly interacted with β-lg via hydrophobic and van der Waals forces, while LU also formed hydrogen bonds. Spectroscopy results indicated carotenoid-induced conformational changes in β-lg. Additionally, carotenoids reduced β-lg's surface hydrophobicity and increased its particle size and absolute zeta potential in a concentration-dependent manner. Furthermore, molecular dynamics simulations further confirmed conformational changes in the complexes. The findings offer valuable insights into the interaction mechanism between proteins and carotenoids from a molecular perspective.