The peroxidizing effect of α‐tocopherol on autoxidation of methyl linoleate in bulk phase

Abstract

In order to understand the effect of α-tocopherol on the autoxidation mechanism of edible oil under storage conditions, methyl linoleate was allowed to autoxidize at 50 C in bulk phase without any radical initiator. The reaction was monitored by determining the production of four isomeric hydroperoxides (13-cis,trans; 13-trans,trans; 9-cis,trans; 9-trans,trans) by high performance liquid chromatographic analysis after reduction. In the absence of α-tocopherol, the rate of autoxidation depended on the sample size, and the duration of the induction period was affected by the initial level of hydroperoxides. However, the distribution of c-t and t-t hydroperoxide isomers remained constant during the propagation period regardless of the sample size. The addition of α-tocopherol at 0.1 and 1.0% caused a linear increase in the amount of hydroperoxides and elevated the distribution of the c-t isomers. The rate of hydroperoxidation appeared to be governed by the initial concentration of α-tocopherol rather than the sample size or the initial hydroperoxide level. This peroxidizing effect of α-tocopherol was suppressed by the presence of ascorbyl palmitate. A mechanism in which chromanoxy radical participates is proposed for the effect of α-tocopherol on lipid autoxidation in bulk phase. It is therefore suggested that α-tocopherol at high concentrations influences the mechanism of autoxidation of edible oil.

Vitamin E: Mechanism of Its Antioxidant Activity.

“…Methyl linoleate containing 0.5 mol% cY-tocopherol showed a linear accumulation of MeLOOH with depletion of the c!-tocopherol. Therefore, c!-tocopherol at a high concentration acts as a pro-oxidant (Cillard et al, 1980;Terao & Matsushita, 1986). The main products were 3, 5, c!-tocopherol dimer (6) and c!-tocopherol trirner (7) in the 0.5-g sample.…”

“…c!-Tocopherol at high concentrations induces the formation of lipid hydroperoxides (Peers et al, 1981;Koskas et al, 1984;Terao & Matsushita, 1986). The pro-oxidant effect of c!-tocopherol was related to the reaction of c!-tocopheroxyl radicals with lipids (Terao & Matsushita, 1986;Bowry & Stocker, 1993;Mukai et al, 1993aMukai et al, , 1993b The reaction products of c!-tocopherol with lipid free radicals are described in the following sections.…”

“…Reaction Products of a-Tocopherol during the Autoxidation of Methyl Linoleate cY-Tocopherol inhibits the autoxidation of methyl linoleate in the bulk phase, a-Tocopherol at high concentrations, on the other hand, acts as a pro-oxidant during the autoxidation (Peers et al, 1981;Terao & Matsushita, 1986). Figure 2 shows the possible pathways for the reactions of c!-tocopherol with lipid free radicals.…”

Variability of the composition of fish oils: significance for the diet

“…Vitamin E is an important antioxidant and, thus, helps to inhibit lipid oxidation and the associated production of hydroperoxides, aldehydes, short-chain alkanes, ketones, lactones and polymeric material (Frankel, 1980(Frankel, , 1982(Frankel, , 1984Miyashita et al 1991;Shukla & Perkins, 1991). Lipid peroxides and their aldehydic breakdown products, which are responsible for the off flavours associated with rancid fat (Terao & Matsushita, 1986), are important cytotoxic components associated with oxidative stress and damage (Halliwell, 1993;Parke, 1993). Lipid peroxidation proceeds by a free-radical chain reaction and lipid radicals can cause cell membrane damage and could promote oxidative DNA damage, which may contribute to the aetiology of inflammatory autoimmune diseases such as rheumatoid arthritis as well as cancer.…”

New Potent Antioxidative Hydroxyflavanones Produced withAspergillus saitoifrom Flavanone Glycoside in Citrus Fruit

“…The hydroxyavanone pro duced from hesperidin was identied as 8hydroxy hesperetin (8HHE), a novel substance, and those from naringin were identied as carthamidin (6hydrox ynaringenin) and isocarthamidin (8hydroxynaringenin) by FABMS, 1 HNMR and 13 CNMR analyses. The antioxidative activity of these hydroxyavanones was examined by using the free radicalscavenging system of 1,1diphenyl2picrylhydrazyl (DPPH) and the methyl linoleate oxidation system.…”