Re-assembled oleic acid-protein complexes as nano-vehicles for astaxanthin: Multispectral analysis and molecular docking

In the case of carotenoids, lipid delivery systems are superior in promoting intestinal absorption, while biopolymer-based delivery systems (e.g. protein) have advantages in biocompatibility, biodegradability and controlled release. Therefore, based on the multi-ligand binding properties of protein, we proposed fatty acid-protein complexes as nano-vehicles for encapsulating astaxanthin (ASTA). In this work, oleic acid (OA)–bovine serum albumin (BSA) complexes were fabricated by a pH-driven method. Under the optimized conditions, after OA binding to BSA at a molar ratio of 4:1, slight changes of protein secondary structure appeared and it's surface hydrophobicity increased from 14490 to 25324. When the binding molar ratios of ASTA to BSA ranged from 0.5:1 to 5:1, the ASTA–OA–BSA aqueous dispersions showed better clarity than that of ASTA–BSA. Compared with OA-free BSA, improved encapsulation efficiency and loading capacity were also observed for OA–loading BSA. Based on the fluorescence spectra and Stern–Volmer equation analysis, ASTA binding to the OA-loading BSA displayed a static manner mainly through hydrogen binding and van der Waals interactions. According to the results of site marker competitive experiments and molecular docking, the subdomains IIA and IIIA of BSA should be the acceptor sites of ASTA, and the subdomain IIIA was indicated to be the preferential one. Interestingly, OA as a protein ligand can dramatically enhanced the binding capacity of subdomain IIA to ASTA and make it the preferred acceptor site. In conclusion, OA–BSA nanoparticles as a delivery system should be suitable for fat-soluble nutrients such as carotenoids.