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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Figure 20 Effect of 0, 0.3, 0.6, <strong>and</strong> 1.0 � 10 �3 M �-tocopherol in soybean oil [57].<br />

toward singlet oxygen formation, respectively, <strong>and</strong> C represents the formation of the<br />

oxidized product.<br />

The amount of quencher necessary to inhibit a substantial amount of the singlet<br />

oxygen sensitizer is particularly high <strong>and</strong> the lifetime of the singlet oxygen sensitizer<br />

is very short. For these reasons, singlet sensitizer quenching is not considered in the<br />

steady state equation. Therefore, A is a constant (K) that is equal to the quantum<br />

yield of ISC.<br />

Term B represents the rate of singlet oxygen formation, which is dependent on<br />

the triplet sensitizer quenching rate <strong>and</strong> the rate of triplet–triplet sensitizer annihilation.<br />

Therefore:<br />

k 0 [oxygen]<br />

B = (2)<br />

k [oxygen] � k [quencher]<br />

0 Q<br />

where k 0 is the reaction rate constant of triplet–triplet annihilation <strong>and</strong> k Q is the<br />

reaction rate constant of triplet sensitizer quenching.<br />

Term C represents the formation of oxidized product, which is dependent on<br />

the concentration <strong>and</strong> nature of the substrate, physical <strong>and</strong> chemical quenching of<br />

singlet oxygen, as well as the natural decay rate of singlet oxygen. The assemblage<br />

of these factors generates the following equation:<br />

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

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