Freezing/Thawing 111rapidly deteriorate. Meat that has lost its
attractiveness during frozen storage because
of oxidation of oxymyoglobin on the surface
will remain brown after thawing.
Unwrapped meat thawed in high humidity
air, water, or in steam under vacuum appears
very white and milky after thawing. However,
if then stored in a chill room for 10 to 24
hours, it will be almost indistinguishable
from fresh meat. Unwrapped meat thawed in
air at high temperatures and low humidities
will take on a dark, dry, tired appearance.
It will not recover its appearance during
chilled storage and will often require exten-
sive trimming before sale (James and James
2002 ).
The major problem in retail marketing of
frozen meat is its appearance. The freezing
process causes changes in the structure and
color of the muscle, and the deterioration
in appearance during frozen storage and
display ultimately leads to rejection of the
product by the consumer. Storage tempera-
ture, light intensity on the display area, and
method of packaging all affect the rate of
deterioration. The appearance of fresh meat
is a primary factor in acceptability at retail
level, and the same criteria of attractiveness
will apply to frozen meat, retailed either
frozen or after thawing. The poor color of the
frozen product and the drip associated with
it when it thaws have in the past both con-
tributed to consumer resistance. The appear-
ance of frozen meat is markedly improved if
retail - sized portions are fi rst packed in fi lm
to exclude air between the meat surface and
the fi lm and then rapidly frozen. With this
product, however, the price differential
between fresh and frozen would necessarily
be small, and the consumer would have to be
persuaded by the trade that such frozen meat
was in no way inferior to fresh.Freezing Systems for Meat
Heat transfer can only occur by four
basic mechanisms: conduction, radiation,“ Freezer burn ” is the main appearance
problem that traditionally affected the appear-
ance of meat in frozen storage. Desiccation
from the surface tissues produces a dry,
spongy layer that is unattractive and does not
recover after thawing. This is commonly
called freezer burn. It occurs in unwrapped
or poorly wrapped meat. The problem is
accentuated in areas exposed to low - humid-
ity air at high velocities, and by poor tem-
perature control. Since most meat is now
wrapped and temperature control much
improved, this is less of a problem than it
once was commercially. Provided problems
of freezer burn can be eliminated, the major
appearance problem that affects frozen meat
arises from the oxidation of oxymyoglobin to
metmyoglobin.
Both temperature and illumination level
affect the rate of discoloration during frozen
storage, but light is by far the more serious
factor. Lentz (1971) reported the progress of
discoloration in the light (160 – 220 dekalux)
and in the dark for frozen beef stored at a
range of temperatures in terms of the Munsel
color notation. At − 18 ° C, a temperature
typical of good commercial display, the color
remained attractive for 3 months in the dark
but only 3 days in the light.
There is an interaction between the color
of meat after thawing and its freezing rate.
Jakobsson and Bengtsson (1969, 1973) found
that slowly frozen beef, which darkened on
freezing, also showed considerable loss of
redness after thawing. In contrast, meat
frozen in liquid nitrogen and then defrosted
was a light bright red. Little difference was
also found between thawed beefsteaks that
were frozen at 15 cm h^ −^1 in liquid nitrogen
spray and those that were blast frozen at
4 cm h^ −^1 (Pap 1972 ). In thawed meat, the rate
of pigment oxidation is increased (Cutting
1970 ), and therefore, the color will be less
stable than in fresh. On prolonged frozen
storage, a dark brown layer of metmyoglobin
may form 1 – 2 mm beneath the surface so
that, on thawing, the surface color will