Non-covalent interactions of roselle anthocyanins with milk proteins and egg white protein

Roselle (Hibiscus sabdariffa L.) anthocyanins (RA) provides limited stability against hydration and pH changes during digestion which limit their bio-accessibility. The formation of protein-anthocyanin complexes offers a promising strategy for maintaining the stability of RA. Animal proteins are potential candidates for these interactions due to their high digestibility and balanced essential amino acid profile. In this study, we investigated the interactions of RA with animal proteins, specifically whey protein (WHEY) and casein (CAS) from milk, as well as ovalbumin (OVA) from egg white. Highly purified RA was obtained using XAD-7HP, SCX, and C18 column chromatography to facilitate the study of protein-anthocyanin interactions. Fluorescence spectra indicate that RA bound to the three proteins, leading to the quenching of their intrinsic fluorescence. UV-visible absorption spectra reveal changes in the polypeptide skeletons of the proteins after interacting with RA. Circular dichroism (CD) spectra show alterations in the secondary structure contents of α-helix, β-sheet, β-turn, and random coil upon interaction with RA. Molecular docking studies elucidate the docking active sites of proteins with RA. These interactions resulted in enhanced stability of RA during in vitro simulated digestion for all three proteins. Whey protein emerges as the most promising candidate for enhancing the stability of RA, thereby contributing to the potential application of RA in various food products. Our research provides a theoretical foundation for the utilization of WHEY-RA complexes in beverages and dairy products.