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Composition of tomatoes and tomato products in antioxidants (WG1) page 71
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α-tocopheroxyl . + H + + e - ➔ α-tocopherol
- Stability : - stable to heat and alkalies in the absence of oxygen
- not affected by acids up to 100°C
- slowly oxidized by atmospheric oxygen, rapidly by ferric and
silver salts
- gradually darkens on exposure to light
- The International Unit (IU) of vitamin E is equal to one mg of standard dl-α-
tocopheryl acetate
7.3.2 Occurrence
Found largely in plant materials, present in highest concentrations (0.1-0.3 %) in
wheat germ, corn, sunflower seed, rapeseed, soybean oils, alfalfa and lettuce. Natural α-
tocopherol is usually found together with β-tocopherol and γ-tocopherol.
7.3.3 Antioxidant properties
Vitamin E is the major chain-breaking antioxidant in body tissues and is considered
the first line of defense against lipid peroxidation, protecting cell membranes and lipoproteins
at an early stage of free radical attack through its free radical-quenching activity (Ingold et al.
1987). Upon the chemical repair of, for example, a chain carrying lipid peroxyl radical, α-
tocopherol undergoes a one-electron oxidation to form the α-tocopheroxyl radical (Burton
and Ingold 1986). Although the α-tocopheroxyl radical is generally considered to be poorly
reactive and to serve as a radical sink, under certain in vitro conditions the radical can slowly
abstract a hydrogen atom from the bisallylic methylene groups of polyunsaturated fatty acids
(Ingold et al. 1993). Consequently, as well as being an antioxidant, α-tocopherol can also be
considered to possess pro-oxidant properties, which has been confirmed experimentally
(Yamashita et al. 1998).