Page 374 - Natural Antioxidants, Applications in Foods of Animal Origin

Control of Lipid Oxidation in Muscle Food 353
VetBooks.ir Therefore, the extent of these enzymes activities can be a determining

factor for the different rates of lipid oxidation in meat (Pradhan et al., 2000;
Min & Ahn, 2009).
In addition, some antioxidative peptides can be released from food
proteins. Jurewicz and Salmonowicz (1973) reported that DL-valine,
DL-methionine, OL-proline, and L-cysteine had antioxidant activity. More-
over, milk casein-derived peptides have been shown to have free radical
scavenging activity to inhibit enzymatic and non-enzymatic lipid oxidation
(Suetsuna et al., 2000; Rival et al., 2001a; Rival et al., 2001b).

9.2.1.4.2 Secondary Antioxidants

Secondary antioxidants, in opposite to the primary antioxidants, do not break
free radical chain but are able to stop the lipid oxidation through various
mechanisms (Wasowicz et al., 2004). There are some compounds who act as
secondary antioxidants:

a) Reducing agents

Reductants such as ascorbic acid, which decrease the local concentration of
oxygen, are also able to decrease the formation of peroxyl radicals (Ruiter &
Voragen, 2002). Ascorbate is believed to scavenge tocopherol free radicals
thereby regenerating tocopherol. Ascorbate can also scavenge various free
radicals such as •O , •OOH, and •OH. In addition, ascorbate reduces hyper-
2
−
valent to forms of heme proteins which inhibit lipid oxidation in muscle
foods (Kroger-Ohlsen & Skibsted, 1997).
Although ascorbic acid is mainly recognized as antioxidant, at low
concentrations ascorbic acid may act as a pro-oxidant, especially in the pres-
ence of metal-catalyzed oxidation. Ascorbic acid is able to reduce Fe to
3+
Fe . Nevertheless, the reduced Fe catalyzes the breakdown of hydroper-
2+
2+
oxides to free radicals (as explained above) at a higher rate than Fe (Ponce-
3+
Alquicira, 2006).

b) Chelating agents
As mentioned previously, the presence of metals in fats greatly accelerates
the oxidation process. Inactivation of the catalysis effect of these metals can
be achieved by the use of a sequestering agent (Chu & Hwang, 2002).