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Composition of tomatoes and tomato products in antioxidants (WG1) page 69
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The pro-oxidant activity of vitamin C in vivo is still controversial (Halliwell 1996; Podmore et
al. 1998).
Conclusion for vitamin C
In summary, ascorbic acid is a water soluble vitamin, but unstable in aqueous solutions. It is a
reducing agent, property which confers the molecule its antioxidant character. However, the
pro-oxidant property of the molecule has also to be considered under certain conditions
(presence of iron salt…).
7.3 Vitamin E
Vitamin E is a generic name for 8 naturally occuring compounds with a characteristic
biological activity. Four vitamers are members of the tocopherol family and four are
tocotrienols. Moreover, the stereochemistry of commercially synthesized tocopherols further
complicates structural considerations because there are three asymmetric carbon atoms and
therefore numerous stereoisomers.
The most abundant and active isomer is RRR- α-tocopherol (figure 13). Natural α-
tocopherol as found in foods is RRR- α-tocopherol, whereas chemical synthesis produces a
mixture of eight epimers.
In addition to the α-vitamer, three other tocopherols with biological activity are
present in foods : β-tocopherol, γ-tocopherol, and δ-tocopherol. They differ from α-
tocopherol only in regard to methyl substitutions on the benzene ring. The tocotrienols consist
of four compounds similar to the corresponding tocopherols but with unsaturated side chains.