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.