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Food Lipids: Chemistry, Nutrition, and Biotechnology

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VII. ANTIOXIDANT INTERACTIONS<br />

Biological food systems usually contain multicomponent antioxidant systems. The<br />

numerous existing antioxidants have different potential functions, including inhibition<br />

of prooxidants of different types (e.g., metals, reactive oxygen species, enzymes);<br />

inactivation of free radicals <strong>and</strong> prooxidants in aqueous, interfacial, <strong>and</strong> lipid<br />

phases; <strong>and</strong> inactivation of compounds at different stages of oxidation [e.g., initiating<br />

species (�OH), propagating species (peroxides), lipid oxidation decomposition products<br />

(aldehydes)]. In addition, multicomponent antioxidant systems are beneficial<br />

because direct interactions occur between antioxidants.<br />

Combinations of chelators <strong>and</strong> FRS often result in synergistic inhibition of lipid<br />

oxidation [6]. Synergistic interaction most likely occurs by a ‘‘sparing’’ effect provided<br />

by the chelator. Since the chelator will decrease oxidation rates by inhibiting<br />

metal-catalyzed oxidation, fewer free radicals will be generated in the system. This<br />

means that the eventual inactivation of the FRS through reactions such as termination<br />

or autoxidation will be slower, thus making its concentration greater at any given<br />

time. The combination of chelator <strong>and</strong> FRS thus decreases free radical generation<br />

<strong>and</strong> increases radical scavenging potential.<br />

Synergistic antioxidant activity can also be observed by the combination of<br />

two or more different FRS. This occurs when one FRS reacts more rapidly with free<br />

radicals than the other as a result of differences in bond disassociation energies <strong>and</strong>/<br />

or stearic hindrance of FRS/ROO� interactions [6]. These differences will result in<br />

one antioxidant being consumed faster than the other. However, it may be possible<br />

for this FRS to be regenerated by transfer of its radical to a different scavenger. In<br />

the system consisting of �-tocopherol <strong>and</strong> ascorbic acid [106], for example, �-tocopherol<br />

is the primary FRS because it is present in the lipid phase. Ascorbic acid<br />

then regenerates the tocopheroxyl radical or possibly tocopherylquinone back to �tocopherol<br />

plus the semihydroascorbyl radical [4], which dismutases to dehydroascorbate<br />

[3]. In turn, dehydroascorbate may be regenerated by enzymes that utilize<br />

NADH or NADPH as reducing equivalents [107].<br />

Since multicomponent antioxidant systems can inhibit oxidation at many different<br />

phases of oxidation, the resulting antioxidant activity can be synergistic. This<br />

suggests that the most effective antioxidant systems for foods would contain antioxidants<br />

with different mechanisms of action <strong>and</strong>/or physical properties. Determining<br />

which antioxidants would be most effective depends on factors such as types of<br />

oxidation catalyst, physical state of lipid (bulk vs. emulsified), <strong>and</strong> factors that influence<br />

the activity of the antioxidants themselves (e.g., pH, temperature, the ability<br />

to interact with other compounds in the foods).<br />

REFERENCES<br />

1. N. I. Krinsky. Mechanism of action of biological antioxidants. Proc. Soc. Exp. Biol.<br />

Med. 200:248 (1992).<br />

2. J. L. Boll<strong>and</strong> <strong>and</strong> P. ten Have. Kinetic studies in the chemistry of rubber <strong>and</strong> related<br />

materials: IV. The inhibitory effect of hydroquinone on the thermal oxidation of methyl<br />

linoleate. Trans. Faraday Soc., 42:201 (1947).<br />

3. G. R. Buettner. The pecking order of free radicals <strong>and</strong> antioxidants: Lipid peroxidation,<br />

�-tocopherol, <strong>and</strong> ascorbate. Arch. Biochem. Biophys. 300(2):535 (1993).<br />

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

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