Page 43 - Natural Antioxidants, Applications in Foods of Animal Origin

22 Natural Antioxidants: Applications in Foods of Animal Origin
VetBooks.ir in dark muscle than in ordinary muscle of both sardine and mackerel. Satu-

ration of red color in meat was directly related to myoglobin concentration
(Faustman et al., 1992). Other constituents of meat including enzymatic and
non-enzymatic reducing systems can accelerate oxidation by converting iron
from the inactive ferric form to the active ferrous state (Foegeding et al.,
1996). Changes of PV, conjugated diene (CD) and TBARS in sardine muscle
indicated that lipid oxidation occurred throughout 15 days of iced storage.
Apart from a plenty of unsaturated fatty acids, heme protein as well as reac-
tive iron in the muscle might contribute to the accelerated oxidation (Chaijan
et al., 2006).
Under fluctuating oxygen supply and pH decrease of post mortem system,
the heme pigments like hemoglobin and myoglobin become catalytic in
lipid peroxidation by mechanisms involving both one- and two-electron
transfer processes, which are different from mechanisms for lipid oxida-
tion by the non-heme-iron LOX (Carlsen et al., 2005). Reeder and Wilson
(1998) suggested that myoglobin plays a role of photosensitizer which may
be responsible for the initial formation of lipid hydroperoxides and increase
the rate of oxygen uptake of fish oil via a photosensitized oxidation.

1.6.1 ROLE OF DEOXYMYOGLOBIN IN LIPID OXIDATION

The physiologically active myoglobin species are the purple high-spin iron
(II) myoglobin (deoxymyoglobin), which has the sixth coordination site
of the heme iron vacant, and the bright cherry-red low-spin oxy-iron (II)
myoglobin (oxymyoglobin), which bind a molecule of oxygen at the sixth
coordination of the heme iron, due to their high affinity for oxygen (Baron
& Andersen, 2002; Faustman et al., 1999; Gorelik & Kanner, 2001). Distur-
bance of the globin structure can result in binding of the unusual ligands
(e.g., the distal histidine in the heme cavity, exogenous amino acids as histi-
dine and methionine, or a hydroxyl group) at the sixth coordination of the
heme iron and induce the formation of a low-spin iron (II) species, known
as hemochromes. Hemochromes in its oxidation state II can be found either
reversible (binding to the imidazole group of the distal histidine or hydroxyl
ion) or irreversible (binding to the imidazole group of free histidine) (Baron
& Andersen, 2002).
The study regarding prooxidative activity of deoxymyoglobin in biolog-
ical system including muscle foods is scarce (Baron & Andersen, 2002).
This is mainly due to the fact that deoxymyoglobin initiated lipid oxidation
demands strictly anaerobic condition; to exclude oxymyoglobin initiated