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Table 3.3 Hydroperoxides formed by oxidation of fatty acids with singlet and triplet
oxygen
Fatty acid
Oleate
Linoleate
Linolenate
Singlet oxygen
Saturated hydroperoxides
9-OOH
10-OOH
Conjugated hydroperoxides
9-OOH
9-OOH
13-OOH
12-OOH
13-OOH
16-OOH
Non-conjugated hydroperoxides
10-OOH
10-OOH
12-OOH
15-OOH
Triplet oxygen
Saturate hydroperoxides
8-OOH
9-OOH
10-OOH
11-OOH
Conjugated hydroperoxides
9-OOH
9-OOH
13-OOH
12-OOH
13-OOH
16-OOH
From Frankel et al. (1979).
analysis of the oxidation breakdown products therefore allows differentiating
between the types of oxygen that may cause the oxidation.
3.2.4 Methods to study singlet oxygen in foods
Detection and evaluation of singlet oxygen in foods
Singlet oxygen detection in food oxidation of foods is difficult due to the short
lifetime of the excited molecule. Several analytical
techniques have been
developed for the detection of singlet oxygen.
Spectrophotometric methods can be used to measure singlet oxygen
indirectly. These methods use a compound of which absorption at a suitable
wavelength decreases after reaction with singlet oxygen. In organic solvents the
molecule 1,3-diphenylisobenzofuran can be used since it reacts readily with
singlet oxygen. This reaction results in decreased absorbance at 410 nm
(Kochevar and Redmond, 2000). In aqueous systems para-nitrosodimethyl-
alanine can be monitored at 440 nm absorbance as the molecule reacts with an
imidazole intermediate.
Another interesting molecule for indirect detection of singlet oxygen is
cholesterol as it reacts with singlet oxygen to form specific oxidation products,
more specifically hydroperoxides. The specificity even allows differentiation of
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