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. Fe 3+ and Cu 2+ enhanced particle integrity by forming stable metal–polyphenol networks, while Al 3+ and Zn 2+ 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, Fe 3+ /Cu 2+ imparted strong pH stability to the carriers, Al 3+ /Mg 2+ /Zn 2+ preserved β-carotene under light/heat/oxygen conditions, and Al 3+ /Zn 2+ 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.