Antioxidant activities and interactions of α- and γ-tocopherols within canola and soybean emulsions

During the 1940s, basic theories addressing the chemistry of lipid oxidation were developed, namely the free radical theory of hydroperoxide formation and decomposition and its inhibition by antioxidants. Tocopherols, especially the α- and γ-homologs, are the primary antioxidants in vegetable oils. α-Tocopherol having a fully substituted phenolic ring has a stronger power than γ-tocopherol in scavenging free radicals in solutions but this is not consistently the case in foods, including vegetable oils and their emulsions. Paradoxical results on the superiority of these two closely related antioxidants over each other are often found. The article by Moser et al. in this issue of the European Journal of Lipid Science and Technology presents a comprehensive study comparing the antioxidant activities of α- and γ-tocopherols and their interactions in 10% canola and soybean oil-in-water emulsions incubated at 50°C. The oxidation of stripped oils, supplemented with known concentrations of α- and/or γ-tocopherols, was followed by measuring the evolution of hydroperoxides and their decomposition product hexanal. The results were affected by the oil matrix. In canola oil emulsions, γ-tocopherol was a stronger antioxidant than α-tocopherol (at 200 or 600μg/g oil) and their interaction was additive even at 600+600μg/g oil level. In soybean oil emulsions, α-tocopherol was the stronger antioxidant at concentrations up to 250μg/g oil while γ-tocopherol was the stronger antioxidant at the higher concentrations and the interaction between the two tocopherols was synergistic at the low concentrations (200+200μg/g oil) but was either additive or antagonistic at higher concentrations. In both oils, α-tocopherol lost antioxidant effectiveness at around 400μg/g oil.