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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Figure 3 Structures of tocopherols <strong>and</strong> tocotrienols.<br />

antioxidant source for foods marketed under an ‘‘all-natural’’ label. They are permitted<br />

in foods according to GMP regulations (21 CFR 182.3890). Natural tocopherols<br />

are limited to 0.03% (300 pp in animal fats) (9 CFR 318.7). Because of the<br />

high vitamin E content of most vegetable oils, addition of tocopherols can lead to<br />

prooxidant activity [18].<br />

The antioxidative mechanism of �-tocopherol is well understood. �-Tocopherol<br />

donates a hydrogen to a peroxy radical resulting in a �-tocopheryl semiquinone<br />

radical [Eq. (16)]. This radical may further donate another hydrogen to produce<br />

methyltocopherylquinone [Eq. (17)] or react with another �-tocopheryl semiquinone<br />

radical to produce an �-tocopherol dimer [Eq. (18)]. Higher polymeric forms can<br />

then form.<br />

ROO� ��-tocopherol → ROOH � �-tocopheryl semiquinone� (16)<br />

�-tocopheryl semiquinone� �ROO� → ROOH � methyltocopherylquinone<br />

(17)<br />

�-tocopheryl semiquinone� ��-tocopheryl semiquinone� → �-tocopherol dimer<br />

(18)<br />

The methyltocopherylquinone is unstable <strong>and</strong> will yield �-tocopherylquinone.<br />

The �-tocopheryl dimer continues to possess antioxidant activity. Numerous other<br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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