Probing the mechanism of antioxidant and oxidative stability properties of gallic acid and its esters in natural esters: Computational investigations and experiments

Natural polyphenols are commonly used as antioxidants in oil-based systems due to their strong antioxidant activity and safety profile. However, their hydrophilic nature limits their solubility in oils, a limitation that can be addressed by converting them into hydrophobic lipophenols through esterification. In this study, the antioxidant activity and oxidative stability of gallic acid and its ester derivatives in natural ester oils were investigated. Density functional theory and molecular dynamics simulations were conducted to elucidate the antioxidant mechanisms of gallic acid esters. The results indicate that gallic acid esters form stable hydrogen-bonded complexes with natural ester molecules, and the lower reaction barrier with ROO• radicals facilitates effective interactions between the antioxidants and oil molecules, thereby enhancing antioxidant efficacy. Among the derivatives, C2-GA demonstrates superior antioxidant activity due to its lowest reaction barrier with ROO• radicals and the stability of its hydrogen-bonded complexes with natural esters. This aligns well with experimental findings, as differential scanning calorimetry (DSC) tests show that C2-GA increases the oxidation induction time (OIT) of natural ester oils by 119 %, significantly enhancing oxidative stability. Additionally, C2-GA exhibits strong radical scavenging ability in the DPPH radical assay, further supporting its high antioxidant potential. These results demonstrate that this computational approach can effectively predict the antioxidant potential of gallic acid esters, facilitating the rational design of new polyphenolic antioxidants for applications in oil-based systems.