Tocopherols vitamin stability

The same is true of antioxidants like BHT (butylhydroxytoluene). Although it is used in purified form in human and animal food, its more common use is as a stabilizer for polymers and lubricants. Only BHA (butylhydrox-yanisole), a-tocopherol (vitamin E), TBHQ (tertiary-butylhydroquinone) and propylgal-late, which are marketed by Eastman Kodak, can be considered as purely food antioxidants for the two reasons that they are not toxic and that they are high priced. In fact, Eastman Kodak is the only chemical leader to produce an extended range of food additives mono-and diglycerides and vitamins. 

Interest in the antioxidant properties of the naturally occurring para-alkoxyphenol a-tocopherol (vitamin E) led to cyclic voltammetry (CV) studies on the radical cations (XXXV) and dications (XXXVI) of model compounds (XXXIV). Both the dication and phenoxonium ion (XXXVII) were found to possess surprising stability when prepared in MeCN [43,44] ... 

Product stability and performance can be affected by exposure to several oxidative sources, including oxygen, free radicals, UV radiation, oxidative enzymes, catabolic oxidation, and chemical oxidation. Many antioxidants are also good UV absorbers due to their conjugated chemical structure. Typical antioxidants found in cosmetic products are flavonoids, polyphenols, carotenoids, thiols, tocopherol (vitamin E) and ascorbic acid (vitamin C) [71,72], According to Black [73], a combination of antioxidants from different classes is more effective than a single antioxidant due to an antioxidant cascade mechanism. 

In packaging, three resins account for the majority of the market for antioxidants PP, PE, and HIPS. For PP, a combination of hindered phenol and phosphite antioxidants is commonly used, with the total concentration normally from 0.08 to 1%, depending on formulation and end use. Clba Specialty Chemicals has developed the phenolic antioxidant family of Irganox for use in PP and PE, and also the Irgafos family, which are phosphite stabilizers used in combination with phenolic antioxidants. For LDPE, BHT, a phenolic antioxidant, is normally incorporated at levels of 50 to 500 ppm however there is a tendency to employ less volatile additives to prevent their migration from the resin. For HDPE and LLDPE, antioxidants less volatile than BHT, such as polyphenols, at higher concentrations, are normally used In combination with phosphites. For HIPS, hindered phenols are used in combination with UV absorbers. Alpha-tocopherol (Vitamin E) is sometimes used as an antioxidant for polyolefins. 

Buckley, J. and Connolly, J.F. (1980) Influence of alpha-tocopherol (vitamin E) on storage stability of raw pork and bacon. J. Food Protect. 43, 265-267. 

Although there are several compounds (Ascorbic acid (vitamin C) or alpha-tocopherol (vitamin E) which their antioxidant effect is proved to be effective in reducing the oxidation of UHMWPE [60], there are several studies that support the antioxidant capacity of carbon nanotubes (CNTs). For example, in the study of Zeynalov et al. [61] was conducted a simulation of thermo-oxidative processes which take place in the polymer chains, and the results showed an inhibition of oxidation of the polymer when carbon nanotubes are present. Also, P. Castell et al. [62] founded that the incorporation of low concentration of arc-discharged multiwall carbon nanotubes (MWCNTs) can act as inhibitors of the oxidative process on irradiated UHMWPE, proving the radical scavenger effect of this reinforcing material. Also, this study shows that the presence of MWCNTs enhances the chemical stability of the polymer. 

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... 

Another approach to safer stabilization is to use a biological antioxidant such as vitamin E (a-tocopherol is the active form of vitamin E, AO-9, Table la). It is essentially a hindered phenol which acts as an effective chain breaking donor antioxidant, donating a hydrogen to ROO to yield a very stable tocopheroxyl radical, a-Tocopherol is a very effective melt stabilizer in polyolefins that offers high protection to the polymer at very low concentration [41], (Table 2). 

The effect of vitamin E supplementation on a-tocopherol and /(-carotene concentrations in tissues from pasture- and grain-fed cattle was also elucidated with HPLC analysis. The investigation was motivated by the fact that a-tocopherol influences beneficially meat colour and stability [53], and the presence of /(-carotene can modify the amount of a-tocopherol in tissues [54], Samples were extracted with hexane and the concentration of /(-carotene was assessed by HPLC. Some data are listed in Table 2.20. It was concluded from the data that... 

Choy et al. [193] reported that vitamin A (retinoic acid), vitamin C (ascorbic acid) and vitamin E (tocopherol) could be intercalated into Zn/Al LDHs by the coprecipitation method. In solutions, these vitamins are normally all sensitive to light, heat and oxygen, and it was proposed that incorporating the molecules into a layered inorganic lattice may lead to their stabilization, resulting in a wider range of potential apphcations. 

For instance, the radical of a-tocopherol (the radical of vitamin E) is immediately protonated to form the a-tocopherol cation-radical. The high stability of this cation-radical in mild acidic conditions is unusual when compared with many other phenols, which readily deprotonate even in strong acidic conditions (see a review by Webster 2007). 

Antioxidants are compounds that inhibit autoxidation reactions by rapidly reacting with radical intermediates to form less-reactive radicals that are unable to continue the chain reaction. The chain reaction is effectively stopped, since the damaging radical becomes bound to the antioxidant. Thus, vitamin E (a-tocopherol) is used commercially to retard rancidity in fatty materials in food manufacturing. Its antioxidant effect is likely to arise by reaction with peroxyl radicals. These remove a hydrogen atom from the phenol group, generating a resonance-stabilized radical that does not propagate the radical reaction. Instead, it mops up further peroxyl radicals. In due course, the tocopheryl peroxide is hydrolysed to a-tocopherylquinone. 

Milk contains some important vitamins. The vitamin D content niav vary from. 10 I.U. per quart in summer to 6 in winter, depending upon the Iced and the sunlight which reach the cow. Both pasteurized and evaporated milk are often fortified by the addition, on a fluid basis, of 400 I.U. of vitamin D per quart. Vitamins A. D, and F. (alpha-tocopherol) are fal-soluble and stable at the heat treatments used in processing milk and milk products. The remaining stlamlns arc water-soluble and of varying stability Vitamins B,... 

If hydrogen transfer is under thermodynamic control, then the vitamin will experience cleavage of the weakest CH (or OH) bond. Compare energies of radicals derived from hydrogen abstraction at different positions from a model a-tocopherol (R = CH3). Which radical is most stable Are there alternative radicals of similar stability ... 

Vitamin E is a generic term that represents four tocopherols and four tocotrienols of varying biological potency. The term tocopherol correctly refers to the methyl-substituted derivatives of to-col and is not synonymous with the term vitamin E. The tocopherols and tocotrienols may be referred to collectively as tocochromanols. Many of the diverse deficiency syndromes observed in animals experimentally deprived of vitamin E can be explained by the vitamin s acting as an antioxidant in stabilizing unsaturated lipids in biological membranes. 

Urano, S., Kitahara, M., Kato, Y., Hasegawa, Y., and Matsuo, M. (1990). Membrane stabilizing effect of Vitamin E existence of a hydrogen bond between alpha-tocopherol and phospholipids in bilayer membranesJ. Nutr. Sci. Vitaminol., 36, 513-519. 

Urano, S. etal., Membrane stabilization of vitamin E interactions of alpha-tocopherol with phospholipids in bilayer liposomes, Biochem. Biophys. Res. Commun., 146, 1413, 1987. 

Erin, A.N. et al., Stabilization of synaptic membranes by alpha-tocopherol against the damaging action of phospholipases. Possible mechanism of biological action of vitamin E, Brain Res., 398, 85, 1986. 

Normal-Phase Chromatography Example. Vitamin E, an antioxidant, is a complex made up of tocopherols and tocotrienols (Figure 8-62), which are sometimes used to stabilize formulations. Tocopherols are a series of related benzopyranols with a C16 saturated side chain. Tocotrienols contain three double bonds on the C16 side chain [32]. 

Schmutz CW, Martinelli E, Miihlebach S. Stability of vitamin Kj assessed by HPLC in total parenteral nutrition (TPN) admixtures. Clin Nutr 1992 ll(suppl) 110-lll. Billion-Rey F, Guillaumont M, Frederich A. Stability of fat-soluble vitamins A (retinol pabnitate), E (tocopherol acetate), and Kj (phylloquinone) in total parenteral nutrition at home. J Parent Enter Nutr 1993 17 56-60. 

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