Meat Packaging 249order to maintain bloom, with at least 20%
CO 2 to prevent selective microbial growth
(Eilert 2005 ). Whether these gases were
placed in the primary package or in a master
bag surrounding the primary package, the
basic technology has been unchanged for a
number of years. This technology has been
successful for a number of larger retailers, as
the shelf life provided by this package has
been suffi cient for usage in a controlled dis-
tribution system (Eilert 2005 ). High O 2 MA
packs contain atmospheres of O 2 and CO 2 ,
and often N 2. Mixtures of O 2 /CO 2 have been
used commercially for a considerable time
(Brody 1970 ). A patent in 1970 specifi ed a
range of O 2 and CO 2 concentrations suitable
for MAP beef (Georgala and Davidson 1970 ).
Results demonstrated that at least 60% O 2 is
required to achieve a color shelf life of 9
days, and the patent claims that a mixture of
80% O 2 plus 20% CO 2 keeps meat red for up
to 15 days at 4 ° C (Georgala and Davidson
1970 ). Typically, fresh red meats are stored
in MAP containing 80% O 2 :20% CO 2
(Georgala and Davidson 1970 ), while cooked
meat equivalents are stored in 70% N 2 :30%
CO 2 (Smiddy et al. 2002 ).
Beefsteaks are commonly displayed under
high oxygen concentrations in MAP in order
to promote color stability (Zakrys et al.
2008 ). As previously stated, the major func-
tion of O 2 is to maintain the muscle pigment
myoglobin in its oxygenated (oxymyoglobin)
form (Kerry et al. 2006 ), but high oxygen
levels within MAP also promote oxidation of
muscle lipids over time (O ’ Grady et al.
1998 ). These high O 2 levels may also impact
negatively on the oxidative stability of
muscle lipids and lead to the development of
undesirable fl avors (Rhee and Ziprin 1987 ;
Estevez and Cava 2004 ). This distinctive off -
fl avor develops rapidly in meat that has been
precooked, chilled - stored, and reheated. The
term warmed - over - fl avor (WOF) has been
adopted to identify this fl avor deterioration
(Renerre and Labadie 1993 ). Membrane
phospholipids are particularly susceptible tostored in air and held at similar temperatures.
Also, the shelf - life extension of bacon by
packaging in CO 2 - enriched atmospheres was
investigated by Callow in 1932 (Callow
1932 ). Additionally, in the 1930s a carbon
dioxide - enriched environment was employed
to transport refrigerated beef carcasses from
Australia and New Zealand (Floros and
Matsos 2005 ). The retail use of MAP did not
occur until the 1950s, in the form of vacuum
packaging (Floros and Matsos 2005 ). In
1981, Marks & Spencer introduced to the
United Kingdom gas - fl ushed fresh meat in
plastic trays (Inns 1987 ). It is now used ubiq-
uitously across the meat industry for many
different meat products. As previously stated,
MA packs usually contain mixtures of two or
three gases.
The use of high O 2 concentrations in MA
packs promotes oxymyoglobin (OxyMb) for-
mation, the cherry red form of myoglobin
(O ’ Grady et al. 2000 ). Packaging beef in MA
packs and storing at low temperatures extends
the product shelf life considerably (Young
et al. 1983 ). Beef and lamb are both red
meats and share similar properties, but con-
siderable differences in shelf lives are
apparent between them due to their relative
susceptibility to chemical and microbial
spoilage. In contrast to beef cuts, much of the
surface of lamb is adipose tissue, which has
a pH close to neutrality and has no signifi cant
respiratory activity (Robertson 2006 ). The
pH of beef is lower than that of lamb, thus
making it less susceptible to microbial spoil-
age (Gill 1989 ; Kerry et al. 2000 ). In order
to optimize shelf life, sensory quality, and
microbiological safety using MAP, the pack-
aging system applied must be product spe-
cifi c (Church and Parsons 1995 ).
High O 2 MAP Meat Packs
The vast majority of meat products have been
and continue to be offered in high oxygen
pack formats (approximately 80% O 2 ) in