Page 29 - Natural Antioxidants, Applications in Foods of Animal Origin

8 Natural Antioxidants: Applications in Foods of Animal Origin
VetBooks.ir be involved in initiation of the classical free radical oxidation of lipids

and catalyze other stages of the process. In the presence of light energy-
activated riboflavin, which is a sensitizer, a lipid radical can form, while
oxygen gives rise to superoxide radical anion (O • ). During UV irradiation
−
2
of muscle lipids, the quantity of hydroperoxides and the ratio of their forma-
tion differ, depending on the origin of lipids. For instance, the photooxida-
tion ratio (slope of hydroperoxide accumulation over time of UV exposure
of lipids) of the muscle lipids of fish varied from about one to more than 20,
both within and between the species (Kolakowska, 2002). No correlations
between the photooxidation ratio and monounsaturated fatty acids (MUFA),
PUFA, eicosapentaenoic acid (EPA), or docosahexaenoic acid (DHA)
content in fish lipids were reported (Kolakowska, 2002).
Light induced oxidation is one of the main factors limiting shelf life
of milk. Exposure to visible light leads to off-flavors related to oxidation
of proteins and lipids due to excitation of photosensitizers among which
riboflavin has been recognized to play a major role (Bradley et al., 2003).
Beta-carotene absorbs light in the same region as riboflavin, and it has there-
fore been suggested to protect against photooxidation since less light then
reaches riboflavin (Airado-Rodríguez et al., 2011).
An et al. (2011) studied the effects of sensitizers and pH on the oil
oxidation of acidic O/W emulsions under light by measuring hydroperoxide
content and headspace oxygen consumption in the mixed canola and tuna
oil emulsions. The emulsions consisted of canola and tuna oil (2:1 w/w,
32%), diluted acetic acid (64%), egg yolk powder (4%), chlorophyll b or
erythrosine (5µM), and/or diazabicyclooctane (DABCO) or sodium azide
(0.5M). From the result, chlorophyll increased oil oxidation in the emul-
sion under light via O production while erythrosine did not. In contrast,
1
2
DABCO significantly decreased photooxidation of the oil containing chlo-
rophyll, suggesting O involvement. However, sodium azide increased
1
2
photooxidation of the oil containing chlorophyll possibly via azide radical
production under acidic conditions. The oil photooxidation was higher in
the emulsion containing chlorophyll at pH 6.27 than at pH 2.67 or 3.68,
primarily by O and secondarily by free radicals produced from hydroper-
1
2
oxide decomposition.

1.3.3 ENZYMATIC LIPID OXIDATION

LOX-catalyzed lipid oxidation differs from the free radical reaction by the
formation of hydroperoxides at a certain position of the chain of a free fatty