Location: Functional Foods Research Unit
Title: Antioxidant activities and interactions of alpha- and gamma-tocopherols within canola and soybean oil emulsions Authors
Submitted to: European Journal of Lipid Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 20, 2014
Publication Date: March 25, 2014
Citation: Winkler-Moser, J.K., Logan, A., Bakota, E.L. 2014. Antioxidant activities and interactions of alpha- and gamma-tocopherols within canola and soybean oil emulsions. European Journal of Lipid Science and Technology. 116:606-617. Interpretive Summary: Vegetable oils such as soybean and canola oils are an important source for Vitamin E, which is essential for human growth and development. As an antioxidant, Vitamin E slows the progression of free radical oxidation in the body and also protects vegetable oils and fats in a multitude of food and cosmetic products. The two most common tocopherols are called alpha and gamma tocopherol; these two forms often occur together in vegetable oils. Alpha tocopherol is the strongest Vitamin E form in humans, but gamma tocopherol is usually shown to be a better antioxidant in vegetable oils and food products. The relative strength and optimal concentrations of tocopherols in any given food product are greatly impacted by factors such as the fatty acid composition of the surrounding oil, environmental conditions, and structural features. Oil-in-water (o/w) emulsions, where tiny droplets of oil are stabilized by an emulsifier in an aqueous environment, are common to many food products such as dairy and soy products, beverages, sauces, and salad dressings. Oil may be more susceptible to oxidation under these conditions due to the increased surface area of the oil droplets, and because of the presence of prooxidants in the aqueous phase. It is known that tocopherols can protect emulsions from oxidation, however, the optimal concentrations and the ratio of alpha and gamma tocopherols have not been studied. In addition, the effects of differing oil fatty acid compositions have not been considered. The results of this study show that lipid oxidation is slowed most efficiently in soybean oil emulsions by low concentrations of alpha tocopherol combined with gamma tocopherol. On the other hand, in canola oil emulsions, oxidation was slowed best by high concentrations of gamma tocopherol alone. These results can help food scientists determine the best levels and ratios of tocopherols to protect emulsions depending on the type of oil that is used.
Technical Abstract: The effect of differing concentrations and ratios of alpha- and gamma-TOH on oxidative stability over time was determined by measuring the development of hydroperoxides and volatile secondary oxidation products (hexanal) within a series of oil-in-water (o/w) emulsion systems produced from both canola oil (CO) and soybean oil (SBO). Overall rates for hydroperoxide and hexanal formation were lower in CO than in SBO. In CO emulsions, gamma-TOH was a stronger antioxidant than alpha-TOH, and their interaction in mixtures was additive. In SBO emulsions, alpha-TOH was a better antioxidant at lower concentrations, while gamma-TOH was better at higher concentrations. The interaction between alpha- and gamma-TOH was synergistic at low concentrations, but either additive or antagonistic at higher concentrations, depending on the concentration and ratio of the two TOHs. In both CO and SBO emulsions, alpha-TOH became less effective at higher concentrations, while gamma-TOH activity increased with increasing concentrations.