Investigating α-Tocopherol Role's as Both Anti- and Pro-oxidants in Model Systems

With the increasing interest of replacing synthetic additives with natural alternatives in food products by consumers, α-tocopherol has been studied for years as an antioxidant in lipid processing. In contrast to synthetic antioxidants, the amount used is always a concern for α-tocopherol as it was believed to have a prooxidant effect by accelerating lipid autoxidation at relatively high concentrations. However, increasing concentrations of α-tocopherol are also thought to act as inhibitors of hydroperoxide decomposition, leading to lower concentrations of secondary oxidation products. Due to the complexity of lipid oxidation, monitoring hydroxyl and hydroperoxyl oxidation products is insufficient to evaluate the oxidation level and the antioxidant capacity. In this study, a headspace method was developed to identify and quantify volatile oxidation products, with nonvolatile oxidation products determined by GC-MS simultaneously in a 20-day trilinolein oxidation study with α-tocopherol added at different concentrations. With the developed HS-SPME-GC/MS method, representatives of alkanes(pentane), alkenes(heptene), alcohols(1-pentanol and 1-octen-3-ol), aldehydes(hexanal, 2-octenal and 2-heptenal), ketones(2-heptanone) and furans(2-pentyl-furan) were identified and quantified successfully. As expected, there was a significantly lower amount of all volatile components in trilinolein treated with 2% α-tocopherol, compared to the 0.1% and control group. On the other hand, with nonvolatile oxidation products, the concentrations of 13-hydroxyoctadecadienoic acid were the lowest in the 0.1% group and the highest in the 2% group. Thus, the results from the nonvolatile and volatile oxidation products analysis support the theory that high concentrations α-tocopherol act as a prooxidant by accelerating the primary oxidation pathway as a chain-carrier while also inhibiting the decomposition of the primary oxidation products, resulting in lower concentrations of secondary oxidation products.