Development of a copper-based accelerated oxidation protocol for evaluating the oxidative stability of mayonnaise enriched with hydrophilic and lipophilic grape seed extracts

Lipid oxidation limits the shelf life of oil-in-water emulsions such as mayonnaise, while conventional accelerated tests based on high temperatures may destabilize emulsion structure and distort oxidation kinetics. This study proposes a CuSO₄-assisted accelerated oxidation protocol developed under mild thermal conditions (40 °C), in which the catalyst concentration was systematically screened to establish operating conditions that generated a clear induction phase followed by a quantifiable propagation phase within a 96-h experimental window while maintaining the mayonnaise matrix without visible phase separation throughout the oxidation experiment. Mayonnaise was enriched with hydrophilic grape seed extracts (HE50–150 ppm), a lipophilic grape seed oil macerate (OM, 2.5%), or dual-phase combinations (LHE50–150). Grape seed extracts were characterized for total phenolics, tocopherols, proanthocyanidins, and antioxidant activity using the DPPH radical scavenging assay and the ferric reducing antioxidant power (FRAP) assay. Oxidative stability was assessed using peroxide value (PV) kinetics, UV indices (K232, K270), titratable acidity (TA), lag-time analysis, and kinetic modeling. The predicted time required to reach a common PV threshold (10 meq O₂/kg), extrapolated from the fitted kinetic model beyond the experimental observation period, was used as a comparative indicator of oxidative stability among formulations. Together with UV lag time, this parameter provided the greatest discrimination among formulations. Based on these model-predicted threshold times, dual-phase formulations (LHE100–150) and HE150 exhibited 2.3–2.6-fold longer times to reach the selected PV threshold than the control. Overall, the proposed protocol offers a realistic and practically applicable alternative to high-temperature accelerated tests, and dual-phase antioxidant distribution represents a promising clean-label strategy for stabilizing mayonnaise that warrants further evaluation in other emulsion-based food systems.