Page 387 - Natural Antioxidants, Applications in Foods of Animal Origin

366 Natural Antioxidants: Applications in Foods of Animal Origin
VetBooks.ir attributes through the inhibition or promotion of the growth of the different

microbial groups. MAP inhibits the habitual spoiling microorganisms, but
as will be discussed below favors the development of concrete species that
are responsible for flavor modifications in meat. Regarding lipids, they are
mainly degraded via oxidation processes. Lipid oxidation is linked to pigment
oxidation and discoloration of meat, but also causes flavor deterioration via
the formation of several volatile compounds from the hydroperoxides gener-
ated as products of the primary oxidation. As McMillin (2008) pointed out,
although initial studies did not show enhanced lipid oxidation with increased
O concentrations in MAP, other more recent studies (Cayuela et al., 2004;
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John et al., 2005) reported higher lipid oxidation in meat packaged in high O 2
concentration atmospheres, when compared with vacuum packaged or low
O concentration atmospheres. Other authors, however, clearly reported this
2
problem. Jackson et al. (1992) indicated that oxidative processes cause a real
problem in meat packaged in atmospheres with more than 21% of oxygen.
Unfortunately, this circumstance is the counterpoint to the beneficial effects
already commented of the high O concentrations on the meat color.
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Microbiology and microbial growth during the storage are key factors
in meat quality. Anomalous unpleasant colors and odors, and surface slime
are undesirable effects of microbial growth determining the deterioration
of meat. In MAP, the extended shelf life arises a new issue because patho-
gens have extra-time for development to reach dangerous counts (Farber,
1991). Under normal O concentrations in air, aerobic microorganisms are
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commonly present in meat surfaces, reducing the O tension, promoting
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discoloration, and generating surface slime due to their mobile condition.
MAP notably affects the survival and growth of spoiling and pathogenic
bacteria (Blakistone, 1999). Oxygen stimulates growth of aerobic microor-
ganisms and inhibits the growth of strict anaerobic bacteria, being variable
the sensitivity to the O of the different anaerobic bacterial species (Church,
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1994). Anoxic atmospheres favor the development of lactic acid bacteria and
another facultative anaerobic microorganisms. Nitrogen has minimum effect
on metabolic reactions occurring in meat, but as occurs with some gasses
other than oxygen, the anoxic conditions created by the use of N select
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for anaerobic and facultative anaerobic microorganisms (Thippareddi &
Phebus, 2007). Regarding the effect of CO in atmospheres, gram-negative
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bacteria are in general more sensitive to CO than the gram-positive bacteria,
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because gram-positive bacteria are usually strict or facultative anaerobes
(Farber, 1991). Due to the fact that CO in MAP is firstly absorbed by the
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components of the meat, mainly water, and lipids, until an equilibrium is
reached, an excess of CO should be used to obtain a desired preservative
2