Antioxidants palm tocotrienols

Das, S., Powell, S.R., Wang, R, Divald, A., Nesaretnam, K., Tosaki, A., Cordis, G.A., Maulik, N., and Das, D.K., Cardioprotection with palm tocotrienol antioxidant activity of tocotrienol is linked with its ability to stabilize proteasomes. Am. J. Physiol. Heart Circ. Physiol, 289(1), H361-367, 2005. 

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. 

Tocopherols and tocotrienols, collectively known as tocols, are monophenolic and lipophilic compounds that are widely distributed in plant tissues (7). The main commercial source of natural tocopherols is the soybean oil. Tocotrienols, less common than tocopherols, are present in palm oil, rice bran oil, as well as cereals and legumes (11). Tocopherols and tocotrienols are classified into a-, (3-, y-, and 5-, depending on their chemical structures (Figure 7). In general, tocotrienols have a stronger antioxidant effect on lipid oxidation than tocopherols. The antioxidant activity of tocopherols is dependent on temperature and is in the order of 5- > y->P-> oc-tocopherol (7). Tocopherols (mixed natural concentrate) are a golden... 

Cmde palm oil contains tocopherols and tocotrienols in the range of 600-1000 ppm. Refined palm oil retains about 50% of these products. Tocopherols and tocotrienols are antioxidants and provide some natural oxidative protection to the oil. Table 8 shows the types of tocopherols and tocotrienols present in palm oil. 

Rice bran oil and palm oil are the only readily available oils that contain significant levels (about 1000 ppm) tocotrienols (99). Tocotrienols belong to the Vitamin E family and have similar chemical stmcmres. According to Tomeo et al. (100), tocotrienols are powerful antioxidants. Commercially available RBO may contain 980 ppm y-tocotrienol (101). 

It is important to note the difference between the seed oil and palm oil. Seed oils contain tocopherols. Palm oil contains tocotrienols in addition to tocopherols, and also a small amount of coenzyme QIO. Both tocotrienols and coenzyme QIO high antioxidant properties. Gamma- and delta-tocopherols, and their corresponding tocotrienols, are very effective in protecting oils from autoxidation (37). 

In deep-fat frying, the temperature reaches >170°C, and tocopherols are unstable. The order of stability of different tocopherols remains similar to that at lower temperatures, i.e., a < y < 8 (Gordon and Kourimska, 1995 Lampi and Kamal-Eldin, 1998). However, an opposite order of stability has also been found. During deep-fat frying, the relative stabilities of natural tocopherols and tocotrienols in soybean oil were a-tocopherol > 8-tocopherol > P-tocopherol > y-tocopherol, in corn oil were a-tocopherol > y-tocopherol > 8-tocopherol > y-tocotrienol, and in palm oil were a-tocopherol > S-tocotrienol > a-tocotrienol > y-tocotrienol, respectively (Simonne and Eitenmiller, 1998). The authors assumed that tocotrienols were less stable than tocopherols, because they acted more effectively as antioxidants. 

Crude palm oil is rich in minor components such as carotenoids, tocopherols, tocotrienols, sterols, phospholipids, triterpene alcohols, squalene, aliphatic alcohols and aliphatic hydrocarbons (Goh et al. 1985). The major components of interest are the carotenes, tocopherols, tocotrienols, sterols and squalene (Table 3.10). Carotenes and tocopherols are antioxidants and stabilise the oil against oxidation. During refining, the bleaching and steam deodorisation processes partially remove some of these valuable components. The amounts retained in the refined oils depend on the conditions of refining. 

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