BLBS102-c15 BLBS102-Simpson March 21, 2012 13:21 Trim: 276mm X 219mm Printer Name: Yet to Come
296 Part 3: Meat, Poultry and Seafoodstender than those from a 1/2Angus–1/2Brahman breed, and more
tender than steaks from a 1/4Angus–3/4Brahman breed (John-
son et al. 1990). In other studies, it was found that meat from
Hereford cattle was more tender than that from Brahman cattle
(Wheeler et al. 1990). Differences in the activity of proteolytic
enzymes, especially calpains, that are deeply involved in the
degradation of Z-line proteins appear to have a major role in the
tenderness differences between breeds.
The enzyme fingerprints, which include the assay of many
different enzymes such as endo- and exoproteases as well as
lipases and esterases, are useful for predicting the expected pro-
teolysis and lipolysis during further meat processing (Armero
et al. 1999a, 1999b). These enzymatic reactions, extensively de-
scribed in Chapter 14, are very important for the development
of sensory characteristics such as tenderness and flavor in meat
and meat products.GenesSome genes have been found to have a strong correlation to
certain positive and negative characteristics of meat. The dom-
inant RN-allele, also known as the Napole gene, is common
in the Hampshire breed of pigs and causes high glycogen con-
tent and an extended 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 DL 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 technological yield (Monin and
Sellier 1985).
Pigs containing the halothane gene are stress susceptible, a
condition also known as porcine stress syndrome (PSS). These
pigs are very excitable in response to transportation and envi-
ronmental situations, have a very high incidence of PSE, and
are susceptible to death due to malignant hyperthermia. These
stress-susceptible pigs may be detected through the application
of the halothane test, observing their reaction to inhalation anes-
thesia with halothane (Cassens 2000). These pigs give a higher
carcass yield and leaner carcasses, which constitutes a direct
benefit for farmers. However, the higher percentage of PSE,
with high DL, poor color, and deficient technological properties,
makes it unacceptable to the meat processing industry. These
negative effects convinced major breeding companies to remove
the halothane gene from their lines (Rosenvold and Andersen
2003).Incidence of Exudative MeatsThe detection of exudative meats at early postmortem time is of
primary importance for meat processors to avoid further losses
during processing. It is evident that PSE pork meat is not ap-
pealing to the eye of the consumer because it has a pale color,
abundant dripping in the package, and a loose texture (Cassens
2000). Exudative pork meat also generates a loss of the nutrients
that are solubilized in the sarcoplasm and lost in the drip and an66.577.5pHNormal
PSE
DFD55.50 2 3 4 5 6 7
Postmortem time (hr)Figure 15.8.Typical postmortem pH drop of normal, pale, soft,
exudative (PSE) and dark, firm, dry (DFD) pork meats (Toldra, ́
unpublished).economic loss due to the lower weight as a consequence of its
poor binding properties if the meat is further processed.
PSE meat is the result of protein denaturation at acid pH and
relatively high postmortem temperatures. There are several clas-
sification methodologies, for example, the measurement of pH
or conductivity at 45 minutes postmortem. Other methodolo-
gies involve the use of more data and thus give a more accurate
profile (Warner et al. 1993, 1997, Toldr ́a and Flores 2000). So,
exudative meats are considered when pH measured at 2 hours
postmortem (pH2h) is lower than 5.8 and DL is higher than 6%.
DL, 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,Lis
between 44 and 50, and DL is below 6%. Meats are classified
as DFD whenLis lower than 44 (dark red color), DL is below
3%, and pH measured at 24 hours postmortem (pH24h) remains
high. Typical pH drops are shown in Figure 15.8.
There are some measures such as appropriate transport and
handling, adequate stunning, and chilling 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 mea-
sures, exudative meats still constitute a problem. A survey car-
ried out in the United States in 1992 revealed that 16% of pork
carcasses were PSE, 10% DFD, and about 58% of question-
able quality, mainly RSE, indicating little progress in the re-
duction 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 (Toldr ́aand
Flores 2000).