Vitamin E Tocopherols and Tocotrienols

More recent studies have shown that vitamin E also has roles in cell signaling, by inhibition or inactivation of protein kinase C, and in modulation of gene expression, inhibition of cell proliferation, emd platelet aggregation. These effects are specific for a-tocopberol and are independent of tbe emtiox-idant properties of tbe vitamin. 

Based on biologiccd assay in vitamin E-deficient rats, the vitcuners have widely varying biological activity. The original international unit (iu) of vitamin E potency was equated with the activity of 1 mg of (synthetic) DL-a-tocopherol acetate on this bcisis, pure D-a-tocopherol (i i i -o -tocopherol, the most potent vitamer) is 1.49 iu per mg. The precise mixture of stereoisomers in this original standcud is unknown, and the different stereoisomers have very different biological activities, so that different preparations may differ considerably. 

It is now usual to express the vitcunin E content of foods in terms of milligram-equivalents of (f RR)-a-tocopherol, based on their biological activities. In Table 4.1, the biologiccd activity is shown in iu per milligram and relative to D-a-tocopherol on a molcU basis. For the major vitamers present in foods, total a-tocopherol equivcdent is calculated as the sum of mg a-tocopherol -I- 

/Canadiem Dieteuy Reference inteikes report (Institute of Medicine, 

For a long time, it was considered that, unlike the other vitamins, vitamin E had no specific functions rather it was the major Upid-soluble, radicaltrapping antioxidant in membranes. Many of its functions can be met by synthetic antioxidants however, some of the effects of vitamin E deficiency in experimental animals, including testicular atrophy and necrotizing myopathy, do not respond to synthetic antioxidants. The antioxidant roles of vitamin E and the trace element selenium are closely related and, to a great extent, either can compensate for a deficiency of the other. The sulfur amino acids (methionine and cysteine) also have a vitamin E-sparing effect. 

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Eitenmiller, R.R., and Landen, W.O. Jr. 1999. Vitamin E, Tocopherols and Tocotrienols, in Vitamin Analysis for the Health and Food Sciences. Boca Raton, FL CRC Press, pp. 109-148. 

The Malaysian Palm Oil Board (MPOB), in association with Japanese researchers, developed a patented process (Australian patent PI7565/88) for the extraction of palm vitamin E, and this process has been commercialized. It can produce vitamin E concentrates ranging from 80 to 95% pure. Palm fatty acid distillate (PFAD) containing about 0.4% vitamin E (tocopherols and tocotrienols) is used as the starting raw material in the process. Apart from vitamin E, PFAD contains almost... 

The fat-soluble vitamins can be divided into four different groups, based on biological activity vitamin A (retinol and carotenoids), vitamin D (chole-calciferol and ergocalciferol), vitamin E (tocopherols and tocotrienols), and vitamin K (phylloquinone and menaquinone), all of which may be present in a munber of closely related forms. 

As discussed in A Word About... Vitamin E—Tocopherols and Tocotrienols on page 128, these compounds can be obtained from different sources. How would you convert a-tocotrienol to a-tocopherol ... 

In this chapter, an attempt will be made to highlight the new trends in this area. The approach that was chosen is to briefly summarize the state of the art before 1989, based on the chapters on vitamin E in the two previous editions of this book and an earlier review paper (25-27) and to confront this with the new developments since then. Sections II through V are only concerned with vitamin E sensu strictu—i.e., tocopherols and tocotrienols. The chromatography of stereoisomers, oxidation products, metabolites, and tocopherol analogs is treated separately in sections VI.A through VI.C. 

Tocopherols and tocotrienols belong to the vitamin E family of compounds, which are potent antioxidants. The four isomers of tocotrienols (a-T3, P-T3, y-T3, 8-T3) are structurally related to their corresponding homologues of tocopherols (a-T, p-T, y-T, 8-T), but differ in their side-chain in that T3... 

The main problem in the vitamin E analysis is that it is easily oxidized, thereby an antioxidant, such as butyl hydroxy toluene (BHT) or ascorbic acid, is added to prevent degradation during the extraction step. The traditional method for extraction of tocopherols and tocotrienols in foods is solvent extraction (like soxhlet) and saponification with KOH [457,458]. Some authors have recently proved that saponification is not necessary [459-462], nevertheless, it has been widely applied until the present day. 

Determination of vitamin E isomers in seeds and nuts Determination of tocopherol and tocotrienol in rice bran Investigation of vitamin E content in olives Determination of tocopherol and tocotrienol in olive oils... 

Wehmeyer et al. (1969) published results on the content of B vitamins (thiamine, riboflavin, and nicotinic acid), vitamin C, and p-carotene and foimd that the morama bean is a good source of both B vitamins and vitamin C, but a poor source of p-carotene. Holse et al. (2010) investigated the content of the eight vitamin E isomers and found that the vitamin E composition in morama beans is dominated by y-tocopherol with 59-234 ng/g, followed by a- and p-tocopherols with 14- 8 gg/g and 1.1-3.3 ng/g, respectively. Eurthermore, traces of 8-tocopherol as well as p- and y-tocotrienols were present in some samples. The remaining two tocotrienols (a- and 8-) were not present in the beans. The presence of a-, p-, and y-tocopherols in the morama bean was also foimd by Mitei et al. (2009) who examined morama oil and by Dubois et al. (1995) who examined two samples of T.fassoglense. 

Vitamin E is a collective term for all of the tocopherols and tocotrienols. Of these, one of the most active is (-)-o-tocopherol 6. Lutz Tietze of the Universitiit Gottingen has reported (Angew. Chem. bit. Ed. 2005,44,257) that the Pd-catalyzed cascade cyclization of 4 to 5 proceeds with 96% . 

Currently, high-performance liquid chromatography (HPLC) methods have been widely used in the analysis of tocopherols and tocotrienols in food and nutrition areas. Each form of tocopherol and tocotrienol can be separated and quantified individually using HPLC with either a UV or fluorescence detector. The interferences are largely reduced after separation by HPLC. Therefore, the sensitivity and specificity of HPLC methods are much higher than those obtained with the colorimetric, polarimetric, and GC methods. Also, sample preparation in the HPLC methods is simpler and more efficiently duplicated than in the older methods. Many HPLC methods for the quantification of tocopherols and tocotrienols in various foods and biological samples have been reported. Method number 992.03 of the AOAC International Official Methods of Analysis provides an HPLC method to determine vitamin E in milk-based infant formula. It could probably be said that HPLC methods have become dominant in the analysis of tocopherols and tocotrienols. Therefore, the analytical protocols for tocopherols and tocotrienols in this unit are focused on HPLC methods. Normal and reversed-phase HPLC methods are discussed in the separation and quantification of tocopherols and tocotrienols (see Basic Protocol). Sample... 

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. 

It is fortuitous that indigenous concentrations of vitamin E in the principal food sources are on the order of mg rather than yug/100 g, for the tocopherols and tocotrienols exhibit relatively low intensities of UV absorption. Individual vitamers are characterized by a slightly different absorption maximum within the wavelength range of 292-298 nm in ethanol. Published A] m values for the tocopherols at their Amax in ethanol are a-T 70-73.7 at 292 nm, (3-T 86-87 at 297 nm, y-T 90-93 at 298 nm, and <5-T 91.2 at 298 nm (126). The different absorption characteristics among the vitamers necessitates the running of individual standards for accurate quantitation of each vitamer. The absorption intensity of a-tocopheryl acetate is lower still with an A j m value of only 40-44 at the Amax of 285.5 nm (44). Reported minimum detectable quantities of a-, / -, y-, and (5-tocopherols at 295 nm are, respectively, 50 ng, 70 ng, 90 ng, and 130 ng (127). 

Indyk and Woollard (195) demonstrated that the removal of cholesterol from the un-saponifiable fraction of vitamin D-supplemented whole milk powder by methanolic precipitation and filtration was an adequate cleanup procedure, making semipreparative HPLC unnecessary. This simplified procedure was made possible by connecting two analytical columns in series. The tandem columns adequately separated vitamins D2 and D3 from one another and from vitamins A and E. The analysis of infant formulas (100) required cleanup by silica solid-phase extraction to remove the minor tocopherols and tocotrienols, which constituted potential sources of interference. 

Tocopherols and tocotrienols are precursors of vitamin E and are important antioxidants in oils. Their reactivity means that they are not stable to many oil processing procedures, including deodorization, which reduces levels by up to 15%. Levels of tocopherols in cocoa butter are usually about 100-300 mg/kg, with the y-isomer (IV) being the major component (about 90%), but they can be entirely absent (Lipp et al., 2001) (Figure 3.3). Tocotrienols have a similar structure with unsaturation of alternate bonds along the alkyl chain. Only y-tocotrienol is found in cocoa butter and this at low levels (< 5 mg/kg). Palm oil is notably high in tocopherols and tocotrienols, of which a-tocopherol and a-tocotrienol make up 20% to 30% each with most of the remainder as y-tocotrienol. 

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