Food Lipids: Chemistry, Nutrition, and Biotechnology

Figure 19 Effect of 0, 0.25, 0.5, and 1.0 � 10 �5 M �-carotene on the peroxide value of
soybean oil [57].
20 shows the ability of increasing amounts of �-tocopherol to reduce the head space
oxygen depletion in a model system. The rate of singlet oxygen quenching by �tocopherol
is similar to that of �-carotene.
XV. DETERMINING QUENCHING MECHANISMS
The quenching mechanism of photosensitized singlet oxygen oxidation can be determined
by measuring the rate constant of total quenching, physical quenching, and
chemical quenching. Quenching agents work in numerous ways to inhibit the formation
of oxidized products, as has been previously described (Fig. 18).
The quantum yield of a photochemical reaction is defined as the ratio of the
number of molecules of a product formed to the number of photons of light absorbed.
This value is used to measure the relative efficiency of a photochemical reaction.
The quantum yield of oxidized product formation (�AO 2) can be defined by the
equation:
�AO = A � B � C (1)
2
where A and B represent the partitioning of singlet sensitizer and triplet sensitizer
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.