Interaction of astaxanthin with bovine serum albumin: Role of aggregation state

Astaxanthin-binding proteins contribute to the vibrant coloration of various organisms. Inspired by nature, artificial astaxanthin-protein systems have been developed for food applications. However, due to the structural diversity of proteins and the variable aggregation states of astaxanthin (AST) in aqueous environments, the mechanism underlying color modulation upon astaxanthin-protein binding remains poorly understood. In this study, the interactions between bovine serum albumin (BSA) and astaxanthin in either H-aggregates state (H-AST) or J-aggregates state (J-AST) were investigated using multispectral techniques and molecular dynamics (MD) simulations. H-AST/BSA and J-AST/BSA complexes were prepared using the Solvent-Induced Self-Assembly method. Meanwhile, monomer AST encapsulated BSA complex (M-AST/BSA) was prepared for comparative analysis. The stability of AST states encapsulated in BSA were characterized by ultraviolet-visible absorption spectroscopy. Fluorescence spectroscopy revealed static quenching and decreased binding affinity (M-AST > H-AST > J-AST) of AST for BSA upon the aggregation of AST. The interactions were driven by hydrophobic and electrostatic forces, dominated by both enthalpy and entropy changes. Circular dichroism (CD) showed a decrease in α-helix content and an increase in β-turn structure in BSA upon complexation. Notably, the H-AST/BSA complex underwent a transformation from H- to J-type aggregation by heating from 25 °C to 100 °C, as evidenced by MD simulations. This study provides new insights into the interaction mechanisms between astaxanthin aggregates and BSA. It also establishes a theoretical basis for understanding astaxanthin-protein-related color changes in food systems.