Abstract
Using advanced electron paramagnetic resonance techniques (EPR), oxidation of crude vegetable oils and their components (fatty acids and triglycerides) by radicals generated from hydrogen peroxide was investigated. The correlation rotational times were determined allowing us to characterize radicals formed during edible oils oxidation. Additionally 1H- and 14N-hyperfine coupling constants differentiate the fatty acids dependently on their unsaturation. The acids with a higher number of unsaturated bonds exhibit higher AN values of PBN/·lipid adduct. The waste oil with high free fatty acids content underwent the oxidation reaction more efficiently, however due to saturation and the high content of the fatty acids the carbon-centered radicals formed (upon hydrogen peroxide radicals) and their PBN (N-tert-butyl-α-phenylnitrone) adducts were less stable. The antioxidant effect was dependent on the amount of α-tocopherol added. In small amounts of up to 0.35 mg/1 g of fatty acid or triglyceride, it inhibited the creation of PBN/·lipid adducts while with higher amounts it intensified adduct formation. The α-tocopherol (AT) addition influence was also studied as spin scavenging dependence and indicated that any addition of the antioxidant in the investigated samples led to free radical scavenging and the effect increased with the increase in AT content.
Highlights
The principal features of oils—their stability and quality are dominated by their lipid characteristics
Using advanced electron paramagnetic resonance techniques (EPR), oxidation of crude vegetable oils and their components by radicals generated from hydrogen peroxide was investigated
In this paper we present the results of EPR spectral studies on the oxidation processes of various rapeseed and waste soybean oils and their simpler, expected components: linolenic, linoleic and oleic acid, glyceryl trilinoleate, glyceryl trioleate and a-tocopherol
Summary
The principal features of oils—their stability and quality are dominated by their lipid characteristics. The lipid structure, especially a content of the saturated, mono- or poly- unsaturated triglycerides, is the main indicator of oils oxidative stability and has already been widely investigated [2,3,4,5,6]. The antioxidation process is based on the scavenging of radicals of lipid origin by the tocopherols, in particular by a-tocopherol (AT), leading, in general, to transformation of these antioxidants to new ÁAT radicals. These radicals may further initiate oxidation, implying the well-known dilemma of prooxidant properties of tocopherols [12, 14]. The process is especially intense when the concentration of a-tocopherol is high, other antioxidants present in the system can restrain this prooxidant activity by regeneration of the ÁAT radicals to
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