Page 386 - Natural Antioxidants, Applications in Foods of Animal Origin

Control of Lipid Oxidation in Muscle Food 365
VetBooks.ir Regarding meat color, when the choice is made consumers prefer red

color above purple color, which in turn is preferred above brown color
(Carpenter et al., 2001). Meat color depends on the quantity and form of
the myoglobin pigment. The form of the myoglobin, and its color, depends
on the state of the iron placed in the porphyrin ring in the heme group (that
can be oxidized or reduced) and on the presence or absence of O occupying
2
the sixth coordination site of the iron. Purple color is due to the deoxy-
myoglobin that is the reduced form of myoglobin (Fe ) in the absence of
2+
O (with a vacant sixth coordination site in the iron). Red bright color is
2
due to the oxymyoglobin that is the reduced pigment (Fe ) in which O 2
2+
occupies the ligand position. Oxymyoglobin is usually the form in contact
with the air. Oxymyoglobin is formed by O binding to the ferrous (Fe )
2+
2
ion, which occurs at high O tension values. The penetration of oxygen
2
through the meat and therefore the oxymyoglobin layer thickness depends
upon temperature, O partial pressure, pH, and consumption of O by other
2
2
respiratory processes (Mancini & Hunt, 2005). Brown or gray color is due
to the metmyoglobin form that is the oxidized state of the myoglobin (Fe ).
3+
Metmyoglobin is formed when pigment is exposed for extended times to
light, heat, O , microbial growth, or freezing, all these factors determining
2
the oxidation of the iron to a ferric (Fe ) state. When deoxymyoglobin is
3+
exposed to carbon monoxide, another pigment form, the carboxymyoglobin,
is formed. Carboxymyoglobin formation, with a stable bright-red color,
occurs when CO attaches to the vacant sixth position of deoxymyoglobin,
when the environment is devoid of oxygen. In the absence of CO, the three
other states of the myoglobin may coexist in varying proportions in the same
meat piece depending on redox conditions. The desired bright red-bloomed
color is achieved by the predominance of the oxymyoglobin pigment that
is easily generated when the O percentages in atmosphere are higher than
2
5.5%, and dominates at O percentages higher than 13%. Deoxymyoglobin
2
dominates in atmosphere conditions of less than 0.2% O , while metmyo-
2
globin is the main pigment form at O levels of 0.2–13% (Siegel, 2001).
2
Metmyoglobin is easily formed in fresh meat in the range of 2.6–5.3% of O
2
(Sebranek & Houser, 2006).
Flavor attributes are, together with the tenderness, the most important
factors that influence the consumers’ purchase habits. Compounds deter-
mining flavor and odor are usually originated from protein and lipid compo-
nents of meat (Spanier, 1992). Undesired off-flavors from proteins are
normally generated through the action of microorganisms producing amines,
ammonia, and other odor active compounds such as sulfur compounds,
from amino acids. In this sense, MAP gas composition influences the flavor