Effect of metal types on the controllable supramolecular self-assembly of protein-polyphenol conjugates and their carrier capabilities.

Regulation of different metal ions on the properties, structure, self-assembly and encapsulating capabilities of soybean globulin (SG)-tannic acid (TA) conjugates were investigated. Through coordination interactions, metal ions promoted the supramolecular self-assembly of SG, resulting in the efficient encapsulation of β-carotene in its hydrophobic domains. Fe3+ and Cu2+ enhanced particle integrity by forming stable metal-polyphenol networks, while Al3+ and Zn2+ achieved the highest β-carotene encapsulation efficiency due to their appropriate capability to interact with SG/TA and lower destructive effect on β-carotene. In the presence of TA, Fe3+/Cu2+ imparted strong pH stability to the carriers, Al3+/Mg2+/Zn2+ preserved β-carotene under light/heat/oxygen conditions, and Al3+/Zn2+ promoted superior antioxidant activity and β-carotene bioaccessibility during digestion. These findings demonstrate that metal ions with distinct coordination characteristics significantly influence the functionality of SG-TA conjugates, offering insights for the rational design of metal-induced protein-polyphenol delivery systems.