38 Chapter 2
to suffer from color defects (Halothane+,
Pietrain, and RN - Hampshire). Because color
is a function of rate of pH decline, genetics
can infl uence both the absolute color (dark
pink, pale pink) and the evenness of the
color. Visual two - toning was higher in pork
loins from Duroc cross lines (Duroc/Landrace
and Duroc/Hampshire) than in those from
Pietrain, RN - Hampshire, rn+ Hampshire,
Berkshire, and Large White carcasses. Pork
from Pietrain - sires was lightest and least
pink. The color defects observed in PSE pork
are also linked to postmortem pH decline and
carcass temperature. The abnormal color that
occurs in PSE pork has been duplicated in a
model system by Friese et al. (2005) by
holding chops for 60 to 120 minutes at 42 ° C
or higher. Chops with a pH < 5.8 lightened
until L values (lightness) were similar to
those typical of PSE pork.
PSE pork is undesirable to packers because
of high drip/purge loss, which represents
value lost as “ shrink, ” while the light color
makes PSE pork less appealing to consumers
(Brewer and McKeith 1998 ). Pigs do differ
in susceptibility to PSE regardless of geno-
type. Variation in fi ber type appears to
account for some of this variation because
of myosin isoform - specifi c differences in
denaturation characteristics (Depreux et al.
2002 ).
Animal age and muscle from which the
meat is derived also affect color. L values
of beef from the Psoas major were signifi -
cantly higher (lighter) than those from the
Longissimus lumborum and the Gluteus
medius (Rentfrow et al. 2004 ). L * values
of the latter were higher in meat from year-
ling heifers than in that from two - year - old
heifers.
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