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Food Lipids: Chemistry, Nutrition, and Biotechnology

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4. Enzymatic Antioxidants<br />

Glucose oxidase, superoxide dismutase, catalase, <strong>and</strong> glutathione peroxidase act as<br />

antioxidants by removing from the lipid environment either oxygen or highly oxidative<br />

species. The enzymes just named act biologically to eliminate cellular free<br />

radicals, to keep reactive oxygen species at low concentrations, <strong>and</strong> to catalyze the<br />

destruction of hydrogen peroxide. Thus, they constitute an important biological defense<br />

mechanism against free radical damage. Glucose oxidase is an enzyme that<br />

removes oxygen by using it to produce gluconic acid <strong>and</strong> hydrogen peroxide from<br />

glucose. Commercial glucose oxidase systems include catalase to hydrolyze the hydrogen<br />

peroxide [6].<br />

•�<br />

Superoxide dismutase removes superoxide radicals (O 2 ) by converting them<br />

to triplet oxygen ( 3 O2) [Eq. (24)]:<br />

•� � 3<br />

O2 � 2H → HO 2 2 � O 2<br />

(24)<br />

Catalase then converts the hydrogen peroxide to water [Eq. (25)]:<br />

3<br />

HO 2 2 → 2H2O� O 2<br />

(25)<br />

Glutathione dehydrogenase catalyzes the oxidation of glutathione (�-Glu-Cys-<br />

Gly, GSH) in the presence of dehydroascorbic acid. Dehydroascorbic acid acts as a<br />

hydrogen acceptor <strong>and</strong> is returned to its active, free radical scavenging form, ascorbic<br />

acid. Glutathione peroxidase oxidizes glutathione in the presence of hydroperoxide.<br />

The sulfhydryl group on one GSH will react with the sulfhydryl group of another<br />

GSH to produce oxidized glutathione (GSSG) with a disulfide bond [Eq. (26)] [7].<br />

ROOH � 2GSH → ROH � HO� GSSG (26)<br />

2<br />

Glucose oxidase, catalase, <strong>and</strong> superoxide dismutase are used commercially as<br />

antioxidants in various foods.<br />

5. Proteins <strong>and</strong> Related Substances<br />

Numerous amines, amino acids, peptides, <strong>and</strong> protein hydrolyzates have antioxidant<br />

activity. A comprehensive list of all the proteinaceous antioxidant sources is not<br />

presented here. Amines have been shown to possess antioxidant activity. Recently,<br />

spermine <strong>and</strong> spermidine isolated from fish sources were used to inhibit fish oil<br />

oxidation [28]. Numerous amines such as hypoxanthine <strong>and</strong> xanthine can be readily<br />

isolated from marine sources. Amino acids have chelating abilities, but also exhibit<br />

antioxidant activity when used alone. Glycine, methionine, histidine, tryptophan, proline,<br />

<strong>and</strong> lysine are effective antioxidants in oil [6].<br />

Proteins <strong>and</strong> protein hydrolysates possess antioxidative factors. Iron-binding<br />

proteins such as ferritin <strong>and</strong> transferritin have antioxidant function. Histidine-containing<br />

peptides such as carnosine [29], as well as synthetic peptides [30] <strong>and</strong> peptides<br />

obtained from protein hydrolysis [31,32], possess antioxidant activity. Glutathione<br />

tripeptide (�-Gly-Cys-Gly, GSH) has antioxidant activity, which is mediated<br />

by the sulfhydryl group of cysteine <strong>and</strong> glutathione peroxidase. The sulfhydryl group<br />

on one GSH will react with the sulfhydryl group of another GSH to produce oxidized<br />

glutathione (GSSG) with a disulfide bond. Glutathione/glutathione peroxidase was<br />

effective in preventing lipid oxidation in a minced mackerel system [33]. In addition,<br />

GSH can form disulfides with proteins or other thiols [34]. It is capable of acting as<br />

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

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