Chain length-dependent antioxidant performance of phospholipid complexes of alkyl gallates in walnut oil and emulsions: A proposed localization-based mechanism.

Phospholipid complexes of gallic acid and alkyl gallates (C1-C16) were synthesized and applied to walnut oil to investigate their antioxidant efficacy and underlying mechanisms. They exhibited significantly enhanced antioxidant efficacy over the monomers or physical mixtures during thermal oxidation (60 °C). Our systematic structure-activity relationship study revealed that complexes with intermediate (C4) and longest (C16) alkyl chains exhibited the highest antioxidant efficacy, as evidenced by reduced oxidation products and degradation of polyunsaturated fatty acids. Critical micelle concentration, cryo-TEM, CLSM, and SAXS analysis collectively indicated that the complexes self-assembled into reverse micelles in oil. Based on this, a spatial distribution mechanism was proposed: The alkyl chain length appeared to achieve complementary antioxidant protection at interfacial and lipid regions by influencing the preferential positioning of complexes within these structures. Similar trends were observed in oil-in-water emulsions. These findings provide mechanistic insights into the rational design of phospholipid-based antioxidant systems for lipid-rich foods.