Multi-spectroscopies and molecular docking insights into the interaction mechanism and antioxidant activity of astaxanthin and β-lactoglobulin nanodispersions

In this study, interaction mechanism of astaxanthin (AST) with β-lactoglobulin (β-La) nanodispersions that were prepared by emulsification-evaporation method was investigated using multi-spectroscopies and molecular docking. Further, the antioxidant activity of the resultant nanodispersions was evaluated. The AST was successfully bound to the β-La and spontaneous interaction between β-La and AST complex was established. Hydrophobic interactions between β-La and AST were the dominant force that maintained the binding affinity. The nanodispersions were characterized by a static quenching of intrinsic fluorescence of the β-La, an increased particle size of β-La and AST complex and a decreased surface hydrophobicity of β-La. Molecular docking investigation of the nanodispersions elucidated that a linear molecule of AST was partly inserted into the hydrophobic core of β-La, which located at the internal cavity of β-barrel of β-La and encompassed by hydrophobic amino acid residues. The binding between β-La and AST significantly (P < 0.05) enhanced 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) radical scavenging activity and intracellular reactive oxygen species scavenging ability of AST. The ABTS scavenging ability of AST in β-La/AST nanodispersion was almost four-fold higher than that of the individual AST. This study provided evidence that suggests the incorporation of AST in dairy products could have great potential to enhance the functionality of the dairy products and convey better activity than the individual components.