13 Biochemistry of Raw Meat and Poultry 305Genes
Some genes have been found to have a strong corre-
lation to certain positive and negative characteristics
of meat. The dominant RN-allele, also known as the
Napole gene, is common in the Hampshire breed of
pigs and causes high glycogen content and an ex-
tended pH decline. The carcasses are leaner, and the
eating quality is better in terms of tenderness and
juiciness, but the more rapid pH fall increases drip
loss by about 1%, while the technological yield is
reduced by 5–6% (Rosenvold and Andersen 2003,
Josell et al. 2003). The processing industry is not
interested in pigs with this gene because most pork
meat is used for further processing, and the meat
from carriers of the RN-allele gives such a low tech-
nological yield (Monin and Sellier 1985).
Pigs containing the halothane gene are stress sus-
ceptible, a condition also known as porcine stress
syndrome (PSS). These pigs are very excitable in
response to transportation and environmental situ-
ations, have a very high incidence of PSE, and
are susceptible to death due to malignant hyperther-
mia. These stress-susceptible pigs may be detected
through the application of the halothane test, observ-
ing their reaction to inhalation anesthesia with halo-
thane (Cassens 2000). These pigs give a higher car-
cass yield and leaner carcasses, which constitutes a
direct benefit for farmers. However, the higher per-
centage of PSE, with high drip loss, poor color, and
deficient technological properties, makes it unac-
ceptable to the meat processing industry. These neg-
ative effects recently convinced major breeding
companies to remove the halothane gene from their
lines (Rosenvold and Andersen 2003).
Incidence of Exudative Meats
The detection of exudative meats at early postmor-
tem time is of primary importance for meat proces-
sors to avoid further losses during processing. It is
evident that PSE pork meat is not appealing to the
eye of the consumer because it has a pale color,
abundant dripping in the package, and a loose tex-
ture (Cassens 2000). Exudative pork meat also gen-
erates a loss of the nutrients that are solubilized in
the sarcoplasm and lost in the drip and an economic
loss due to the loss of weight as a consequence of its
poor binding properties if the meat is further pro-
cessed.
PSE meat is the result of protein denaturation at
acid pH and relatively high postmortem tempera-
tures. There are several classification methodologies,
for example, the measurement of pH or conductivity
at 45 minutes postmortem. Other methodologies in-
volve the use of more data and thus give a more
accurate profile (Warner et al. 1993, 1997; Toldrá
and Flores 2000). So exudative meats are considered
when pH measured at 2 hours postmortem (pH2h) is
lower than 5.8 and drip loss (DL) is higher than 6%.
Drip loss, which is usually expressed as a percent,
gives an indication of water loss (difference in
weight between 0 and 72 hours): a weighed muscle
portion is hung within a sealed plastic bag for 72
hours under refrigeration, then reweighed (Honikel
1997). The color parameter, L, is higher than 50
(pale color) for PSE meats and between 44 and 50
for red exudative (RSE) meats. Meats are considered
normal when pH2his higher than 5.8, L is between
44 and 50, and drip loss is below 6%. Meats are
classified as dark, firm, and dry (DFD) when L is
lower than 44 (dark red color), drip loss is below
3%, and pH measured at 24 hours postmortem
(pH24h) remains high. Typical pH drops are shown in
Figure 13.8.
There are some measures such as appropriate
transport and handling, adequate stunning, and chill-
ing rate of carcasses that can be applied to prevent,
or at least reduce, the incidence of negative effects
in exudative meats. Even though the problem is well
known and there are some available corrective
measures, exudative meats still constitute a problem.
A survey carried out in the United States in 1992
revealed that 16% of pork carcasses were PSE, 10%
DFD, and about 58% of questionable quality, main-
ly RSE, indicating little progress in the reduction of
the problem (Cassens 2000). A similar finding was
obtained in a survey carried out in Spain in 1999,
where 37% of carcasses were PSE, 12% RSE, and
10% DFD (Toldrá and Flores 2000).EFFECT OF THEAGE ANDSEXThe content in intramuscular fat content increases
with the age of the animal. In addition, the meat
tends to be more flavorful and colorful, due to an
increased concentration of volatiles and myoglobin,
respectively (Armero et al. 1999b). Some of the
muscle proteolytic and lipolytic enzymes are affect-
ed by age. Muscles from heavy pigs (11 months old)