Interfacial localization of lecithin complexes of gallic acid esters improves the antioxidant performance of rapeseed oil

Lecithin complexes enable chain-length-dependent interfacial localization of gallates. • Pre-assembled lecithin-gallate complexes form reverse micelles at oil-water interfaces. • Complexes outperform physical mixtures by overcoming the “polar paradox” in bulk oils. • L-E3:0 Com inhibited primary oxidation, whereas L-E12:0 Com limited secondary products. • L-E3:0 Com and L-E12:0 Com may be associated with distinct interfacial environments. The antioxidant performance of phenolic compounds in bulk oils depends on both radical-scavenging capacity and interfacial localization. Gallic acid esters (GA-Es) are effective radical scavengers, but their performance is limited by the polar paradox and cut-off effect, limiting their interfacial accumulation. Here, soybean lecithin (LEC) was complexed with gallic acid (GA) and GA-Es (C1-C16), and compared with free antioxidants and physical mixtures in rapeseed oil. Spectroscopy and molecular docking indicated non-covalent association between gallate hydroxyl groups and the phospholipid headgroup; DPPH and ABTS assays confirmed retained radical-scavenging capacity. During accelerated storage at 60 °C, the lecithin-propyl gallate complex (L-E3:0 Com) and lecithin-dodecyl gallate complex (L-E12:0 Com) provided the greatest protection against lipid oxidation, with L-E12:0 Com particularly limiting 4-hydroxy-2-hexenal accumulation. The apparent critical micelle concentrations of the complexes (49.71-75.05 μmol/kg oil) were 24.6-50.0% lower than that of LEC (99.47 μmol/kg oil). Cryo-TEM and SAXS revealed formation of heterogeneous association colloids, while fluorescence probing revealed chain-length-dependent differences in local interfacial hydration. Dynamic light scattering and interfacial-tension measurements exhibited corresponding non-monotonic trends: L-E3:0 Com formed the smallest assemblies (8.48 ± 0.98 nm) and produced the lowest oil-water interfacial tension (14.35 ± 0.17 mN/m), whereas long-chain complexes formed larger structures and showed stronger hydrophobic association. These results indicate that lecithin complexation modulated gallate aggregation and interfacial behavior in a chain-length-dependent manner, providing a plausible physicochemical basis for the two antioxidant optima observed for L-E3:0 Com and L-E12:0 Com.