Tocopherol, as antioxidant

The use of tocopherols as antioxidants in pharmaceuticals and food products is unlikely to pose any hazard to human health since the daily intake from such uses is small compared to the intake of naturally occurring tocopherols in the diet. 

Special care was taken to minimise exposure to light. Samples were tak to dryness and resu ended in prc an-2-ol/hexane/water/methanQl (56/38.5/3.3/2.2 v/v) for HPLC s aration. All solutions used for the extraction and storage of lipids contained 0.01 % butylated hydroxytcluene and 0.2 % o(-tocopherol as antioxidants. Galactolipids were separated and analysed a modification of the gradient HPLC method of Heemskerk et al. (7). 

The potency of the tocopherols as antioxidants enables them to protect many of the readily oxidizable constituents of fats, including carotene and vitamin A. Some of the work in this field was reviewed briefly by Mason in Volume 2 of this series (1944). Golumbic.(2) studied the action of tocopherols in stabilizing animal fats and related substances, and found that their antioxidant power was shared by hydroxychromans and hy-droxycoumarans. Quackenbush, Cox, and Steenbock (3) found that... 

Jakobsson and Sivik [47] also used ascorbic acid and a-tocopherol as antioxidants to prevent oxidation of fish oil. The a-tocopherol (0.06%) was incorporated in the oil phase, whereas the ascorbic acid was solubilized in the aqueous phase of the w/o microemulsion, whose composition was 77% fish oil, 20% distilled monoglyceride, and 3% aqueous phase. Oxidation was monitored by measuring the peroxide and anisidine values. A drastic reduction in oxidation was observed when antioxidants were incorporated in the microemulsion system. Oxidation was found to decrease further when ascorbic acid was dissolved in glycerol instead of water. A possible reason for this decrease in oxidation is that there is high internal mobility among the molecules and very short distances between the two phases. This promotes the internal mixing and the ability of the antioxidants to meet and scavenge the free radicals. 

The most popular natural antioxidants on the market are rosemary extracts and tocopherols. Natural antioxidants have several drawbacks which limit use. Tocopherols are not as effective ia vegetable fats and oils as they are ia animal fats. Herb extracts often impart undesirable colors or flavors ia the products where used. In addition, natural antioxidants cost considerably more than synthetic ones. Despite this, the pubHc s uncertainty of the safety of synthetic antioxidants continues to fuel the demand for natural ones (21). 

As metal ions catalyze peiroxidation reactions, glass-distilled water should be used and chelating agents can be added to the medium. (5) The dispersions should not be exposed to y irradiation. (6) Antioxidant can be added to the system. a-Tocopherol, buty-lated hydroxytoluene, butyl hydroxyanisole, and ascorbic acid have been proposed as antioxidants. 

The poor results with the two phenols were unexpected in view of their effectiveness as antioxidants in emulsions. R, Stadnick and A, Govil investigated the effect of a-tocopherol in a system identical to that used in the present study except for the absence of the oil phase (14), They found that after incubation for 90 hours, the recovery of nitrite in the presence of a-tocopherol was half that observed in its absence. 

Vitamin E consists of a family of related compounds, the tocopherols. The most abundant in the American diet is 7-tocopherol and, although it is potentially superior in the detoxification of nitrogen dioxide, the biochemistry of a-tocopherol is considered more relevant to cardiovascular disease (Kayden and Traber, 1993). Vitamin E undoubtedly has several modes of action in vim. The most clearly understood of these, at the chemical level, is the role of a-tocopherol as an antioxidant. 

It has been proposed that the a-tocopheroxyl radical can be recycled back to tocopherol by ascorbate producing the ascorbyl radical (Packer etal., 1979 Scarpa et al., 1984). The location of a-tocopherol, with its phytyl tail in the membrane parallel to the fatty acyl chains of the phospholipids and its phenolic hydroxyl group at the memisrane-water interface near the polar headgroups of the phospholipid bilayer, enables ascorbate to donate hydrogen atoms to the tocopheroxyl radical. The suitability for ascorbate and tocopherol as chain-breaking antioxidants is exemplified (Buettner,... 

The lag-phase measurement at 234 nm of the development of conjugated dienes on copper-stimulated LDL oxidation is used to define the oxidation resistance of different LDL samples (Esterbauer et al., 1992). During the lag phase, the antioxidants in LDL (vitamin E, carotenoids, ubiquinol-10) are consumed in a distinct sequence with a-tocopherol as the first followed by 7-tocopherol, thereafter the carotenoids cryptoxanthin, lycopene and finally /3-carotene. a-Tocopherol is the most prominent antioxidant of LDL (6.4 1.8 mol/mol LDL), whereas the concentration of the others 7-tocopherol, /3-carotene, lycopene, cryptoxanthin, zea-xanthin, lutein and phytofluene is only 1/10 to 1/300 of a-tocopherol. Since the tocopherols reside in the outer layer of the LDL molecule, protecting the monolayer of phospholipids and the carotenoids are in the inner core protecting the cholesterylesters, and the progression of oxidation is likely to occur from the aqueous interface inwards, it seems reasonable to assign to a-tocopherol the rank of the front-line antioxidant. In vivo, the LDL will also interact with the plasma water-soluble antioxidants in the circulation, not in the artery wall, as mentioned above. 

Tocopherols are not as effective as antioxidants as the synthetic antioxidants, e.g. BHA or BHT. The antioxidant effect of tocopherols is increased by mixing them with ascorbyl palmitate, ascorbic acid, lecithin or citric acid. Typical confectionery applications are the use of tocopherols with ascorbyl palmitate or lecithin or citric acid in the fat phase of toffees or caramels. Chewing gum base can be treated with a- and y-tocopherol to extend the shelf life. 

The provision of fat-soluble vitamins and lipids is difficult, if not impossible, in various diseases. This is especially true for diseases that are accompanied by a lot of oxidative stress, for example, mucoviscidosis. The requirements of fat-soluble antioxidative substances are certainly high in these cases and can barely be covered by intramuscular injections because fat-soluble vitamins can hardly, if at all, be absorbed from oily preparations. Alternatively, the vitamins can administered via the buccal mucosa the fat-soluble substances have to be packaged in such a way that they can be transported in a watery compartment and are thus able to largely dissolve in the saliva. When they have an adequate size, they can then penetrate the buccal mucosa. One approach is the development of the so-called nanocolloids, that is, particles with a polar nucleus, in which the fat-soluble vitamin is dissolved, and an apolar wrapping (monolayer). This structure makes an oral application of fat-soluble substances possible. First tests demonstrated that vitamin A palmitate, a-tocopherol, as well as coenzyme Qio are thus able to enter the systemic circulation via the buccal mucosa. 

The presence of a-tocopherol, together with smaller quantities of p- and y-toco-pherols, should not be surprising since these are natural antioxidants found in both egg yolk and vegetable oils and are usually regarded as useful contaminants. However, some manufacturers are known to be adding up to 0.2% of the a-tocopherol as an antioxidant. 

Tobacco mosaic virus 247, 334s, 336s Tocopherols 392,815 — 822,818 as antioxidants 822 a-Tocopherol (vitamin E) 819s Tocopherolquinone 818, 819, 819s Tocotrienols 818 Togavirus 247... 

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