Improving C-phycocyanin photostability by forming complexes with organic acids: l-ascorbic acid, ferulic acid and cinnamic acid

C-phycocyanin (CPC) is a natural pigment-protein complex that is widely used for its vivid blue color and bioactive properties in the food, cosmetics, and biomedical fields. However, its widespread use was limited due to its poor photostability. This study aimed to improve the photostability of CPC and investigate the mechanism by forming non-covalent complexes with three organic acids with different antioxidant properties: l -ascorbic acid, cinnamic acid, and ferulic acid. Spectroscopic analysis showed that organic acid binding induced alterations in CPC's secondary structure, slightly reducing α-helix content while increasing β-sheet formation, without disrupting the tetrapyrrole chromophore. Computational docking analysis indicated that organic acids slightly changed the protein conformation by adjusting the spatial arrangement of amino acids surrounding the chromophore. This study shows organic acids improve CPC's photostability, aiding its use as a natural blue food pigment.