Effect of fatty acids and tocopherols on the oxidative stability of vegetable oils

Abstract

Effect of fatty acids and tocopherols on the oxidative stability of vegetable oilsThe oxidative stability of vegetable oils is determined by their fatty acid composition and antioxidants, mainly tocopherols but also other non-saponifiable constituents. The effect of fatty acids on stability depends mainly on their degree of unsaturation and, to a lesser degree, on the position of the unsaturated functions within the triacylglycerol molecule. Vegetable oils contain tocopherols and tocotrienols, especially a-and gtocopherols, as their main antioxidants. The antioxidant behavior of tocopherols represents a complex phenomenon as they are efficient antioxidants at low concentrations but they gradually lose efficacy as their concentrations in the vegetable oils increase. The "loss of efficacy" of tocopherols, sometimes referred to as a "pro-oxidant effect", is witnessed by an increase in the rate of oxidation during the induction period, despite elongation of this phase. The phenomenon is much obvious for a-tocopherol, but is also evident for other tocopherols. In agreement with nature's wisdom, the tocopherol levels in vegetable oils seem to be close to the optimal levels needed for the stabilization of these oils. The presence of other antioxidants in the oils, e.g. carotenoids, phenolic compounds, and Maillard reaction products, may synergize with tocopherols and minimize this loss of efficacy.

Effect of pretreatment on the proximate composition, physicochemical characteristics and stability of <em>Moringa peregrina</em> oil

“…The oxidative stability of vegetable oils depends on the fatty acids composition (saturated, unsaturated, number and position of the double bonds, etc.,) as well as the presence and amount of antioxidants (tocols, plastochromanol, pigments, phenolic compounds and others). Vegetable oils having high levels of oleic acid are known to have better resistance to oxidation compared to those containing higher levels of linoleic and linolenic acids (Kamal-Eldin, 2006). In the present study, oleic acid represented more than 70% of the total fatty acids and linoleic as well as linolenic acids were detected in a minor amount in the case of the germinated sample only (0.8%).…”

γ-Tocopherol as a Marker of Brazilian Coffee (Coffea arabica L.) Adulteration by Corn

“…The % contamination was arbitrarily chosen and based on the supposition that it had to be sufficiently high for a financial return but at the same time could not be too high as to significantly alter the coffee's flavor. As we have seen, tocopherol content is affected by variety in both coffee and corn, and tocopherols are also susceptible to loss through oxidation and heat (26); thus, the tocopherol content in coffee could also be influenced by processing and storage parameters. Therefore, we determined that the most straightforward method for detecting corn contamination would be to focus on changes in the tocopherol peak area percentages rather than on total tocopherol content.…”

Vitamin and fatty acid contents in seeds of some taxa belonging to genusLathyrusL. growing in Turkey

“…Antioxidants are barrier against free radicals which is responsible for a number of malfunctions in biological tissues (Yanishlieva et al, 2002;Sahin et al, 2005). Generally tocopherols are recognized as the important antioxidants in vegetable oils mainly because of their lipophilicity (Verleyen et al, 2002 ;Kamal-Eldin, 2006). They protect polyunsaturated fatty acids from oxidative degradation and their antioxidant effect is a result of their ability to donate their phenolic hydrogens to lipid peroxyl radicals (Yanishlieva et al, 2002).…”