304 Part III: Muscle Foods
lactic acid accumulation produces a relatively rapid
(in a few hours) pH drop to values of about 5.6–5.8.
The pH drop rate depends on the glucose concentra-
tion, the temperature of the muscle, and the meta-
bolic status of the animal previous to slaughter. Water
binding decreases with pH drop because of the
change in the protein’s charge. Then, some water is
released out of the muscle as a drip loss. The amount
of released water depends on the extent and rate of
pH drop. Soluble compounds such as sarcoplasmic
proteins, peptides, free amino acids, nucleotides,
nucleosides, B vitamins, and minerals may be partly
lost in the drippings, affecting nutritional quality
(Toldrá 2004).
The pH drop during early postmortem has a great
influence on the quality of pork and poultry meats.
The pH decrease is very fast, below 5.8 after 2 hours
postmortem, in muscles from animals with acceler-
ated metabolism. This is the case of the pale, soft,
exudative pork meats (PSE) and red, soft, exudative
pork meats (RSE). ATP breakdown also proceeds
very quickly in these types of meats, with almost
full ATP disappearance in less than 2 hours (Batlle
et al 2001). Red, firm, normal meat (RFN) experi-
ences a progressive pH drop down to values around
5.8–6.0 at 2 hours postmortem. In this meat, full
ATP breakdown may take up to 8 hours. Finally, the
dark, firm, dry pork meat (DFD) and dark cutting
beef meat are produced when the carbohydrates in
the animal are exhausted from before slaughter, and
thus almost no lactic acid can be generated during
early postmortem due to the lack of a substrate. Very
low or almost negligible glycolysis is produced, and
the pH remains high in these meats, which consti-
tutes a risk from the microbiological point of view.
These meats constitute a risk because they are prone
to contamination by foodborne pathogens and must
be carefully processed, with extreme attention to
good hygienic practices.
FACTORS AFFECTING
BIOCHEMICAL
CHARACTERISTICS
EFFECT OFGENETICS
Genetic Type
The genetic type has an important relevance for
quality, not only due to differences among breeds,
but also to differences among animals within the
same breed. Breeding strategies have been focused
towards increased growth rate and lean meat content
and decreased backfat thickness. Although grading
traits are really improved, poorer meat quality is
sometimes obtained. Usually, large ranges are found
for genetic correlations between production and meat
quality traits, probably due to the reduced number of
samples when analyzing the full quality of meat, or
to a large number of samples but with few determi-
nations of quality parameters. This variability makes
it necessary to combine the results from different
research groups to obtain a full scope (Hovenier et
al. 1992).
Current pig breeding schemes are usually based
on a backcross or on a three- or four-way cross. For
instance, a common cross in the European Union is
a three-way cross, where the sow is a Landrace
Large White (LR LW) crossbreed. The terminal
sire is chosen depending on the desired profitability
per animal, and there is a wide range of possibilities.
For instance, the Duroc terminal sire grows faster
and shows a better food conversion ratio but accu-
mulates an excess of fat; Belgian Landrace and
Pietrain are heavily muscled but have high suscepti-
bility to stress and thus usually present a high per-
centage of exudative meats; or a combination of
Belgian Landrace Landrace gives good confor-
mation and meat quality (Toldrá 2002).
Differences in tenderness between cattle breeds
have also been observed. For instance, after 10 days
of ageing, the steaks from an Angus breed were
more tender than steaks from a^1 ⁄ 2 Angus–^1 ⁄ 2 Brah-
man breed, and more tender than steaks from a^1 ⁄ 4
Angus–^3 ⁄ 4 Brahman breed (Johnson et al. 1990). In
other studies, it was found that meat from Hereford
cattle was more tender than that from Brahman cat-
tle (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 differ-
ences between breeds.
The enzyme fingerprints, which include the assay
of many different enzymes such as endo- and exo-
proteases as well as lipases and esterases, are useful
for predicting the expected proteolysis and lipolysis
during further meat processing (Armero et al.
1999a, 1999b). These enzymatic reactions, exten-
sively described in Chapter 14, are very important
for the development of sensory characteristics such
as tenderness and flavor in meat and meat products.