Page 26 - Natural Antioxidants, Applications in Foods of Animal Origin

Mechanism of Oxidation in Foods of Animal Origin 5
VetBooks.ir some fermented sausages and the desirable flavor of which does not occur

until hydrolysis of some of the fat and a certain degree of oxidation has taken
place during ripening (Pearson et al., 1977). On the other hand, lipid oxida-
tion during cooking may be a source of intermediate which react with other
components to give important constituents of the desirable flavor of normal
cooked meat (Enser, 1987). The types of flavor developed from the volatile
lipid oxidation compounds depend on a multitude of complex interactions,
concentration ranges, and the medium in which they are tasted (Frankel,
1984). Many of the reactions involved in the formation of volatile aroma
compounds from lipid, follow the same basic pathways for both thermal and
rancid oxidation and similar volatile products are formed. However, subtle
differences in the precise mechanisms of oxidation under storage conditions
and under thermal processing lead to mixtures of volatiles exhibiting both
qualitative and quantitative differences (Mottram, 1987).

1.3 BASIC MECHANISM OF LIPID OXIDATION IN FOODS OF
ANIMAL ORIGIN

The lipid oxidation in foods of animal origin is assumed to proceed along a
free radical route (autoxidation), photooxidation route and enzymatic route.
The oxidation mechanism is basically explained by invoking free-radical
reactions, while the photooxidation and lipoxygenase (LOX) routes differ
from it at the initiation stage only. For this reason, they can be treated as
different forms of free radical reaction initiation.

1.3.1 FREE RADICAL OXIDATION

The two major components involved in lipid oxidation are unsaturated fatty
acids and oxygen. In this process, atmospheric oxygen is added to some
fatty acids, producing unstable intermediates that finally breakdown to
form unpleasant flavor and aroma compounds (Erickson, 2003). Although
enzymatic and photogenic oxidation may play a role, the most common and
important process by which unsaturated fatty acids and oxygen interact is a
free radical mechanism (Erickson, 2003). A free radical reaction or autoxi-
dation is the main reaction involved in oxidative deterioration of food lipids,
including foods of animal origin (Hoac et al., 2006). It is a chain reaction that
consists of initiation, propagation, and termination reactions, and involves
the production of free radicals (Gunstone & Norris, 1983; Nawar, 1996;