Synergistic mechanism of hydrophobic and hydrophilic antioxidants in the interface of tree peony seed oil bilayer emulsion

Interplay between hydrophobic and hydrophilic antioxidants in bilayer emulsions remains unclear, especially within the unique, thicker interface of layer-by-layer assembled systems. This study investigates the antioxidant behavior and interaction mechanism of α-tocopherol (hydrophobic) and l -ascorbic acid (hydrophilic) in tree peony seed oil (TPSO) bilayer emulsions stabilized by whey protein isolate and sodium alginate. At equivalent concentrations, α-tocopherol exhibited stronger antioxidant activity than l -ascorbic acid. When combined, α-tocopherol and l -ascorbic acid yielded a synergistic effect ( Q value = 1.3–1.6). In combined treatments, the proportion of l -ascorbic acid distributed in the aqueous phase decreased compared to its individual use, while its presence at interfacial layer increased correspondingly. This distribution significantly enhanced the oxidative stability of the bilayer emulsion and effectively slowed TPSO degradation. Mechanistically, the close proximity of l -ascorbic acid and α-tocopherol at interface facilitated electron transfer, allowing l -ascorbic acid to regenerate α-tocopherol from its radical form and synergistically enhance oxidative stability.