Contrasting effects of phase-oriented antioxidant localization on oxidative resistance and physical stability of double emulsions

This study investigated the effect of functional antioxidant incorporation and spatial localization on physicochemical and oxidative stability of water-in-oil-in-water (W₁/O/W₂) double emulsions. Paprika oleoresin (PO, lipophilic) in the oil phase and gallic acid (GA, hydrophilic) in the inner (W₁), outer (W₂), and aqueous phases were studied. The effects of antioxidant localization on droplet size, viscosity, ζ-potential, encapsulation efficiency, and oxidative stability were evaluated over four weeks of storage. PO reduced interfacial tension by ~10%, leading to smaller droplets (2.6-2.5 mN/m) and improved oxidative stability. GA in the W₂ phase enhanced radical-scavenging activity (DPPH and ABTS assays) by >30% compared to the control, but decreased ζ-potential (from -32 to -26 mV) and viscosity, leading to increased creaming (≤19%). Dual GA incorporation (W₁ and W₂) showed the highest overall antioxidant capacity but also accelerated pH decline and structural deterioration. These results demonstrate that antioxidant distribution determines destabilization mechanisms in complex emulsions, and phase-oriented interfacial design is essential to balance oxidative protection and structural integrity in multiphase food systems.