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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Figure 4 Chemical reaction steps in the assay of conjugable oxidation products.<br />

1. 2-Thiobarbituric Acid Value<br />

One of the oldest <strong>and</strong> most frequently used tests for assessing lipid oxidation in<br />

foods <strong>and</strong> other biological systems is the 2-thiobarbituric acid (TBA) test. The extent<br />

of lipid oxidation is reported as the TBA value <strong>and</strong> is expressed as milligrams of<br />

malonaldehyde (MA) equivalents per kilogram sample or as micromoles MA equivalents<br />

per gram sample. MA is a relatively minor product of oxidation of polyunsaturated<br />

fatty acids that reacts with the TBA reagent to produce a pink complex<br />

with an absorption maximum at 530–532 nm [27]. The adduct is formed by condensation<br />

of two molecules of TBA with one molecule of MA (Fig. 5). Other products<br />

of lipid oxidation, such as 2-alkenals <strong>and</strong> 2,4-alkadienals, also react with the<br />

TBA reagent. However, the exact mechanism of their reaction with the TBA reagent<br />

is not well understood. There are several procedures for the determination of TBA<br />

values. The TBA test may be performed directly on the sample, its extracts, or<br />

Figure 5 Reaction of 2-thiobarbituric acid (TBA) <strong>and</strong> malonaldehyde (MA).<br />

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

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