Tocotrienols in vegetable oils

C Mariani, G Bellan. Content of tocopherols, deidrotocopherols, tocodienols, tocotrienols in vegetable oils. Riv Ital Sostanze Grasse 73 533-543, 1996. (In Italian.)... 

Cerretani, L. Lerma-Garcia, M.J. Herrero-Martinez, J.M. Gallina-Toschi, T. Simo-Alfonso, E.F. 2009. Determination of tocopherols and tocotrienols in vegetable oils... 

Determination of four tocopherols and four tocotrienols in vegetable oils and fats by the official American Oil Chemists Society method is based on separation by normal-phase HPLC and fluorescence detection (AOCS, 1990). Oil samples are dissolved in hexane, whereas margarines and other fats containing vitamer esters need a cold saponification step to liberate the vitamers. The American Association of Cereal Chemists has a method to analyze vitamin E in various foods. This method (AACC, 1997) is applicable to a vitamin E range of 1 x 10" - 100%, and it includes hot saponification and separation by reversed-phase HPLC. Results are calculated as a-tocopherol acetate. The Royal Society of Chemistry has approved a method to analyze vitamin E in animal feedstuffs by normal-phase HPLC after the vitamers have been liberated by hot saponification (Analytical Methods Committee, 1990). 

AOCS. 1990. Official Method Ce 8-89. Determination of Tocopherols and Tocotrienols in Vegetable Oils and Fats by HPLC, in Official Methods and Recommended Practices of the Am. Oil Chem. Soc. Sampling and Analysis of Commercial Fats and Oils. 4th ed. Champaign, IL Am. Oil Chem. Soc. Press, 5 pp. 

Bonvehi, J. S., Ventura Coll, F., and Rius, I. A. 2000. Liquid chromatographic determination of tocopherols and tocotrienols in vegetable oils, formulated preparations, and biscuits. J. AOAC Inter. 83 627-634. 

Determination of tocopherols in vegetable oils Determination of tocopherols and tocotrienols in rice bran Determination of tocopherols in tomato... 

Ahmed, M.K. Daun, J.K. Przybylski, R. 2005. FT-IR based methodology for quantitation of total tocopherols, tocotrienols, and plastochromanol-8 in vegetable oils. J. Food Comp. Anal. 18 359-364. 

Figure 5. Chromanol ring and isoprenoid side chains in tocopherols, tocotrienols (n = 3), and plastochromanol-8 (n=8, R)=H, R2=CH3 ) in vegetable oils (for systematic names, see Table 6).

TABLE 6. Structures, Trivial, and lUPAC Numbers of Tocopherols, Tocotrienols, and Related Compounds Present in Vegetable Oils. 

Vitamin E was first described ia 1922 and the name was originally applied to a material found in vegetable oils. This material was found to be essential for fertihty in rats. It was not until the early 1980s that symptoms of vitamin E deficiency in humans were recognized. Early work on the natural distributionj isolation, and identification can be attributed to Evans, Burr, and Emerson (University of California) and MattiU and Olcott (University of Iowa). Subsequendy a group of substances (Fig. 1), which fall into either the family of tocopherols or tocotrienols, were found to act likp vitamin E (1—4). The stmcture of OC-tocopherol was deterniined by degradation studies in 1938 (5). 

The tocols (tocopherols and tocotrienols) are the most important class of antioxidants naturally present in vegetable oils and fats. Animal fats only contain trace amounts and this is reflected in their much lower oxidative stability compared with vegetable oils of equivalent degree of unsaturation. Bailey (1951, pp. 61-62) noted many years ago that at high levels tocols can act as prooxidants and that vegetable oils seem to contain near optimum levels for the their fatty acid composition. 

Other common food lipids are the sterols and to-copherols. Sterols are generally present in natural oils as both the free sterol and sterol fatty esters. Animal fats exhibit solely cholesterol while plant lipids contain a range of phytosterols. Tocopherols are found in vegetable oils as a mixture of four iso-mers a-tocopherol (true vitamin E) and 3-, y-, and d-tocopherol. Four unsaturated analogs, tocotrienols, exist with the same numbering terminology and are particularly abundant in palm oil. 

Table 8.5 Ranges and means (mg kg of tocopherol (T) and tocotrienol (T3) levels in vegetable oils... 

E Group active derivatives of tocol and tocotrienol most active is RRR-a-tocoferol = (d)-a-tocoferol Vegetable oils and cereals, vegetables, fruit Depending on the amount of polyunsaturated fatty acids (PUFA) in the diet <1/2 yr 2.9 a-TE 1/2-1 yr 3.6 a-TE 1-19 yr 5.5 up to 13.3 a-TE >19 yr 13 down to 8.3 a-TE pregnancy 0.6 a-TE extra lactating women 2.7 a-TE extra... 

Thirty minutes is sufficient for sample preparation beginning with refined vegetable oils. However, the other sample preparations take up to 120 min because of the incubation, re-extraction, and evaporation steps. Usually, a batch of samples is prepared at the same time to reduce the preparation time per sample. The running time for HPLC analysis is approximately 18 min for normal phase or 14 min for reversed phase in order to quantify all tocols. The running time for normal phase could be cut to 12 min for samples without 5-tocopherol and tocotrienol. 

In some cases, analysis of tocopherols can be used to detect adulteration of oil. Both palm oil and grapeseed oil are relatively unusual in containing significant levels of tocotrienols, which are absent or present at much lower levels in most vegetable oils (Table 6.3). Detection of these compounds can be used to identify adulteration in olive oil at levels as low as 2% (Dionisi et al., 1995). 

The tocopherols and tocotrienols are generally not the major components of vegetable oil, but their presence is vital for stabilizing the unsaturated fatty acids of these oils against oxidative deterioration (39). Their structures are based on a chroman head with two rings, one phenolic and one heterocyclic, and a phytyl tails isoprenoid side chain at C-2. The phytyl tail is saturated in the case of... 

The tocopherol and tocotrienol contents of selected vegetable oils are shown in Table (7). Seed oils are mostly dominated by y- or a-tocopherol, but high levels of 5-tocopherol especially characterize soybean oil, which is the richest and commercially the most used source of tocopherols (46). Rice bran and pahn oils, on the other hand, represent the important sources of tocotrienols (45, 47). Rapeseed... 

TABLE 7. Levels (mg/100 g) of Tocopherol, Tocotrienols, and Related Compounds In Selected Vegetable Oils. 

---