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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Figure 4 Formation of �-tocopherol <strong>and</strong> tocopherylquinone from two �-tocopherol<br />

radicals.<br />

tocopheroxyl <strong>and</strong> peroxyl radicals, which form an addition product ortho to the<br />

phenoxyl oxygen followed by elimination of an alkoxyl radical, addition of oxygen,<br />

<strong>and</strong> abstraction of a hydrogen to form two isomers of epoxy-8�-hydroperoxytocopherone.<br />

Subsequent hydrolysis leads to the formation of epoxyquinones (see Fig. 6 for<br />

an example of this reaction) [9,10]. Formation of epoxide derivatives of tocopherol<br />

represents no net reduction of radicals (because an alkoxyl radical forms) <strong>and</strong> a loss<br />

of tocopherol from the system, whereas any tocopherylquinone that is formed can<br />

be regenerated back to tocopherol in the presence of reducing agents (e.g., ascorbic<br />

acid <strong>and</strong> glutathione; see Sec. VII: Antioxidant Interactions). An additional reaction<br />

that can occur is the interaction of two tocopheroxyl radicals to form tocopherol<br />

dimers [11].<br />

B. Synthetic Phenolics<br />

Phenolic antioxidants for use in foods include synthetic compounds (Fig. 7). Synthetic<br />

phenolic antioxidants exhibit varying polarity, with butylated hydroxytoluene<br />

(most nonpolar) > butylated hydroxyanisole > tertiary butylhydroquinone > propyl<br />

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

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