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Food Lipids: Chemistry, Nutrition, and Biotechnology

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16<br />

Antioxidant Mechanisms<br />

ERIC A. DECKER<br />

University of Massachusetts, Amherst, Massachusetts<br />

I. INTRODUCTION<br />

Krinsky [1] has defined biological antioxidants as ‘‘compounds that protect biological<br />

systems against the potentially harmful effects of processes or reactions that cause<br />

extensive oxidations.’’ While food lipids are derived from biological systems, the<br />

ultimate purpose of food antioxidants is different, since they are used to inhibit<br />

oxidative reactions that cause deterioration of quality (e.g., of flavor, color, nutrient<br />

composition, texture). With this goal in mind, food antioxidants can be defined as<br />

any compounds serving to inhibit oxidative processes that deteriorate the quality of<br />

food lipids. Antioxidant mechanisms that fit this definition include free radical scavenging,<br />

inactivation of peroxides <strong>and</strong> other reactive oxygen species, chelation of<br />

metals, <strong>and</strong> quenching of secondary lipid oxidation products that produce rancid<br />

odors.<br />

Reactive oxygen species <strong>and</strong> free radicals are produced by both enzymic <strong>and</strong><br />

nonenzymic reactions. Therefore, foods usually contain endogenous antioxidants to<br />

protect against oxidative damage. These antioxidant systems often contain several<br />

distinctively different antioxidants for protection against different prooxidative compounds,<br />

including transition metals, heme-containing proteins, enzymes, photosensitizers,<br />

<strong>and</strong> numerous sources of free radicals. Since prooxidants are both water<strong>and</strong><br />

lipid-soluble, endogenous antioxidant systems in foods are usually biphasic. Such<br />

multicomponent <strong>and</strong> biphasic antioxidants represent nature’s own hurdle technology<br />

antioxidant system.<br />

This chapter covers the basic mechanisms by which antioxidants influence oxidative<br />

reactions: inactivation of free radicals, control of oxidation catalysts, inactivation<br />

of oxidation intermediates, <strong>and</strong> interactions between antioxidants <strong>and</strong> secondary<br />

lipid oxidation products.<br />

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

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