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5. Vitamin E

Details

Vitamin E is a very important antioxidant in living beings as well as in the food industry. Vitamin E consists of homologues that are categorized into tocopherols and tocotrienols on the basis of differences in the side chains of these molecules. Furthermore, the structure of the active site, namely the chroman ring, is distinguished into the a type, b type, g type, and d type on the basis of the number of methyl groups and binding positions on the chroman ring. Therefore, in prior literature, it has been suggested that there are 8 kinds of vitamin E homologues.

Fig. 1 Structure of vitamin E homologues

The biological activity of vitamin E indicates the relative biological availabilities of vitamin E homologues in mammals. The relative biological availabilities of vitamin E homologues are thought to be strongly related to the affinity of the respective homologues for a-tocopherol transfer protein (a-TTP) in the liver. Representative values for the biological activities of vitamin E homologues are shown in Table 1. This table suggests that a-tocopherol has the highest biological activity and is the most-needed tocopherol in mammals from the range of vitamin E homologues.

 Table 1 Relative biological availabilities of vitamin E homologues

Recently, however, a novel type of vitamin E has been discovered in salmon roe. This form of vitamin E was named as “marine-derived tocopherol” (MDT) (Fig. 2). The structure of MDT resemblesa-tocopherol, with the exception of the presence of 1 double bond at the terminal end of the phytyl side chain. This tocopherol is distributed in a wide range of marine organisms. Our group confirmed that MDT is also present in processed foods made from fish meat. 
（N. Gotoh, D. Mashimo, T. Oka, K. Sekiguchi, M. Tange, H. Watanabe, N. Noguchi, and S. Wada, Analyses of marine-derived tocopherol in processed foods containing fish. Food Chem. 129,279-283 (2011). [Abstract])

Fig. 2 Structure of MDT

We also examined the relative biological availability of MDT by using a mouse model. Our results show that the relative biological availability of MDT is higher than that of b-tocopherol (Table 2).

Table 2 Relative biological availabilities of MDT

（N. Gotoh, H. Watanabe, T. Oka, D. Mashimo, N. Noguchi, K. Hata, and S. Wada, Dietary marine-derived tocopherol has high biological availability in mice relative to alpha-tocopherol. Lipids 44, 133-143 (2009). [Abstract]）