Food Lipids: Chemistry, Nutrition, and Biotechnology

Figure 21 Singlet oxygen quenching mechanism [58].
k r [substrate]
C = (3)
k [substrate] � (k � k ) [chemical � physical quencher] � k
r ox�Q q d
where k r is the reaction rate constant of the reaction of singlet oxygen with the
substrate, k ox�Q is the reaction rate constant of chemical quenching, k q is the reaction
rate constant of physical quenching, and k d is the decay constant of singlet oxygen.
If a given quenching agent were to inhibit photosensitized oxidation by quenching
singlet oxygen, the steady state equation can be written as:
3
k o [O] 2 k r [A]
3
o 2 Q r ox�Q q d
�AO = K � (4)
k [O]� k [Q] k [A] � (k � k ) [Q] � k
where K is the quantum yield of ISC of the excited state of the singlet sensitizer
[term A from Eq. (1)] and both B and C have been appropriately substituted with
Eqs. (2) and (3), respectively.
Figure 22 Triplet sensitizer quenching mechanism [58].
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.