Page 371 - Natural Antioxidants, Applications in Foods of Animal Origin

350 Natural Antioxidants: Applications in Foods of Animal Origin
VetBooks.ir oxygen-containing compounds, producing radicals that initiate autoxidation

(Frankel, 1998).

9.2.1.3 PRO-OXIDANT FACTORS

a) Metals

Muscle contains notable amounts of iron, a known pro-oxidant, and trace
amounts of copper, which are potent catalysts of lipid oxidation (Richards,
2006). Iron is a part of the active site of lipoxygenase, which may participate
in lipid oxidation (Nabrzyski, 2002). These metals are believed to be pivotal
in the generation of species capable of abstracting a proton from an unsatu-
rated fatty acid (Gutteridge & Halliwell, 1990; Kanner, 1994).
The reaction between ferrous ion and oxygen produce hydrogen peroxide:

Fe + O  Fe + O •
3+
2+
−
2 2
O • + 2H  H O 2
−
+
2
2
Ferrous iron can also then react with H O or preformed lipid hydroper-
2
2
oxides to produce hydroxyl or alkoxyl, and hydroxyl radicals, respectively:
Fe + H O  Fe + OH + •OH −
3+
−
2+
2 2
Fe + ROOH  Fe + •OH + RO •
−
3+
−
2+
b) Heme-proteins
Hemoglobin and myoglobin are the predominant heme-proteins in muscle
foods. Therefore, it is easy to imagine that meat with higher proportion of
heme-proteins (such as pork, beef, or horse) is more susceptible to lipid
oxidation than meat with lower amounts of heme-proteins (such as chicken
or turkey). Similarly, to the above in the section of metals, heme-proteins can
react with lipid hydroperoxides to produce alkoxyl and hydroxyl radicals:

ROOH + Fe -complex  Fe -complex  RO• + OH −
2+
3+
ROOH + Fe -complex  ROO• + H + Fe -complex
3+
2+
+