Mechanism of enhancing the water-solubility and stability of curcumin by self-assembled cod protein nanoparticles at alkaline pH

Curcumin (Cur) is a bioactive phytochemical claimed to have several health-promoting benefits, whose applications are challenged due to its poor water-solubility, chemical instability, and low bioavailability. In this research, the Cur was encapsulated into cod protein (CP) using a pH-driven method to enhance solubility and stability. The physicochemical and structural properties of cod protein-curcumin nanoparticles (CP-Cur) formed were characterized. The Fluorescence Spectroscopy (FL), Ultraviolet spectroscopy (UV), Circular Dichroism (CD), and Dynamic light scattering (DLS) results collectively suggested that the protein with a molten-globule state refolded into a more ordered structure after neutralization, during which Cur was incorporated. Fluorescence Quenching and Isothermal Titration Calorimetry (ITC) further showed that the CP/Cur binding was mainly driven by hydrophobic interaction, resulting in static fluorescence quenching and energy release. Up to 99.50% of Cur was loaded in the CP delivery system. Furthermore, the thermal stability and photostability of Cur were greatly improved due to the protection by protein. The present study proved that cod protein could be a great potential edible carrier for encapsulating curcumin.