Page 372 - Natural Antioxidants, Applications in Foods of Animal Origin

Control of Lipid Oxidation in Muscle Food 351
VetBooks.ir The ability of heme pigments to accelerate the propagation step of the

free-radical chain mechanism can explain the rapid rate of oxidation in
cooked meats (O’sullivan & Kerry, 2012).

c) Enzymes

Various endogenous enzymes are of great importance in the development of
rancidity. The oxidation of fatty acids may occur either directly or indirectly
through the action of enzyme systems, of which three major groups are
involved: microsomal enzymes, peroxidases, and dioxygenases (Erickson,
2002).
Lipoxygenases is capable of the hydrogen abstraction from a polyun-
saturated fatty acid even in polar lipids bound to membrane to generate lipid
hydroperoxides. Therefore, lipoxygenase can be involved in the initiation of
lipid peroxidation of meat (Min et al., 2008).
The off-flavor is due to the volatiles that are produced from breakdown
of the lipoxygenase-derived lipid hydroperoxides (Richards, 2006). These
enzymes may also be responsible for formation of rancid odors by providing
critical amounts of lipid hydroperoxides that can be broken down by metals
or heme-proteins to produce rancid odor.

9.2.1.4 ANTIOXIDANT FACTORS

The addition of antioxidants is the most commonly used method of retarding
lipid oxidation in fat. Antioxidants increase the stability of food components,
especially polyunsaturated lipids, and maintain nutritional value and color
by preventing oxidative rancidity, degradation, and discoloration. However,
it is important to note that any compound that is antioxidative under one set
of conditions can become pro-oxidative under different conditions. As an
example of this point, ascorbate has been found to both inhibit and accel-
erate lipid oxidation depending on the concentration of linoleate hydroper-
oxides in the system (Kanner & Mendel, 1977). In addition, antioxidants are
required to be approved for the intended use. It has been suggested that an
ideal antioxidant food quality should has the following characteristics:

9 no harmful physiological effects
9 absence of undesirable effects on color, odor, or flavor
9 effective at low concentrations