Tocopherols Tocotrienols And Ubiquinones

Unsaponifiable matter present in the extracted oil from oilseeds contain a variety of components, some of which are volatile and may be partially stripped during the deodorization process. The content of tocols, referred to as the total amount of toco-pherols (T) and tocotrienols (T3), varies with the type of oilseed; their distribution is also species-dependent. The members of each of the T and T3 families are designated as alpha, beta, gamma, and delta, depending on the number and position of methyl groups on the chroman ring (Figure 10.3) (Kamal-Eldin and Appelqvist, 1996). Furthermore, there are eight different isomers for each of the tocopherols (three chi-ral centers) and the vitamin E activity of each is based on that of the d-a-tocopoherol, which is an RRR isomer. Other isomers have activities that are always less than that of the natural isomer (Papas, 1999). With respect to their antioxidant activities in vitro, generally 5-and y-tocopherols are most effective tocopherols, and tocotrienols are still more effective than tocopherols (Dziezak, 1986).

In oilseed lipids, there appears to be a direct relationship between the degree of unsaturation, as represented by the iodine value, and the total content of tocopherols (Shahidi and Shukla, 1996). Most vegetable oils contain an abundance of alpha-, gamma-, and delta-tocopherols (Table 10.1), while the beta-isomer is less prevalent, except in wheat germ oil. Meanwhile, tocotrienols are present mainly in palm, rice bran, and wheat germ oils. In view of new developments in the genetic modification of oilseeds, the content and profile of minor components, including those of tocols, may vary considerably in different varieties. However, the importance of seasonal variation, geographical area of cultivation, and degree and type of processing cannot be ignored.

With respect to ubiquinones, also known as coenzyme Q, these compounds occur naturally as 6 to 10 isoprenoid units, designated as Q6 (UQ-6) to Q10 (UQ-10). Coenzyme Q10 (UQ-10) and to a lesser extent UQ-9 (Figure 10.3) have been found in edible oils from vegetable origin (Table 10.1). Ubiquinol is the reduced form of ubiquinone and may protect cell membranes from oxidizing radicals by a direct radical-scavenging mechanism (Halliwell and Gutteridge, 1999). Ubiquinol provides efficient protection in vivo for mitochondria against oxidation, similar to vitamin E in the cell.

Figure 10.3 Chemical structures of tocopherols, tocotrienols, and coenzyme Q's.

OTHER PHYTOCHEMICALS

A wide array of nonphenolic phytochemicals are present in oilseeds (Table 10.2). These include phospholipids, phytosterols, phytic acid, carotenoids, saponins, enzyme inhibitors, lectins and haemagglutinins, glucosinolates, oligosaccharides of sucrose, and cyanogenic glycosides, among others. The following sections provide a cursory account of these phytochemicals in oilseeds.

TABLE 10.1

Tocopoherols (T) and Ubiquinones (UQ) in edible oils (mg/100g)

TABLE 10.1

Tocopoherols (T) and Ubiquinones (UQ) in edible oils (mg/100g)

Oil

a-

T

P-T

y-t

8-T

UQ-9

UQ-10

Canola/rapeseed

17-

-26

35-61.2

0.4-1.2

0.2

7.3

Soybean

10.1-

-10.2

0.27

47.3-59.3

26.4-35.6

0.8

9.2

Sesame

1.0-

-1.8

0.1

24.4-51.2

3.2

3.2

Sunflower

OD ■et

-78.3

0.25

1.9-5.1

0.7-1.0

2.1

0.4

Peanut

13.9-

-26.1

3.0-3.9

13.1-34.3

9.2-2.0

5.4

Cottonseed

38.9

38.7

ND

ND

Evening primrose

16

42

7

ND

ND

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