Metal Ion-Mediated Interfacial Coordination Complexation in Octyl Gallate-Curcumin Emulsions: Enhanced Stability and Curcumin Protection

This study developed an efficient interfacial stabilization strategy, using metal ions (Cu2+) and octyl gallate (OG) to protect curcumin (Cur) via interfacial coordination. Macroscopic observation, droplet size, and Turbiscan stability index analysis demonstrated that the addition of Cu2+ to the OG/Cur emulsion significantly influenced its emulsification efficiency and physical stability, which depended on both the OG concentration and the amount of Cu2+ added. Interfacial rheological analysis showed that Cu2+ addition significantly enhanced droplet interfacial strength, with distinct effects from different metal ions. FT-IR confirmed the coordination bonds of Cu2+ with both Cur (keto/enol) and OG (phenolic hydroxyl). Under appropriate concentrations of OG and Cu2+, the retention rate of curcumin in the emulsion was significantly improved under various processing conditions. After 100 min of UV exposure, the OG/Cur/Cu2+ system increased curcumin retention by 49.64% compared to Cu2+-free systems. The study presents a metal-phenolic coordination-based strategy for constructing stable functional emulsions with high curcumin protection.