Food Biochemistry and Food Processing (2 edition)

BLBS102-c15 BLBS102-Simpson March 21, 2012 13:21 Trim: 276mm X 219mm Printer Name: Yet to Come

15 Biochemistry of Raw Meat and Poultry 295

Figure 15.7.Pork hams after cutting in a slaughterhouse, ready for submission to a processing plant. (Courtesy of Industrias Carnicas ́

Vaquero SA, Madrid, Spain.)

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 experiences 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 pro-

duced 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 constitutes a risk from the microbio-

logical 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.

Protein oxidation is another relevant change during post-

mortem aging. Some amino acid residues may be converted

into carbonyl derivatives and cause the formation of inter- and

intraprotein disulfide links that can reduce the functionality of

proteins (Huff-Lonergan 2010).

FACTORS AFFECTING BIOCHEMICAL

CHARACTERISTICS

Effect of Genetics

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 toward 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 determinations 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 accumulates an excess of fat; Belgian Landrace and

Pietrain are heavily muscled but have high susceptibility to stress

and thus usually present a high percentage of exudative meats;

or a combination of Belgian Landrace×Landrace gives good

conformation and meat quality (Toldr ́a 2002).

Differences in tenderness between cattle breeds have also been

observed. Brahman cattle is used extensively in the southwest

of the United States since it is tolerant to adverse environmental

conditions but may give some tenderness issues (Brewer 2010).

Even toughness was associated to an increased amount of calpas-

tatin, the endogenous muscle calpain inhibitor (Ibrahim 2008).

Studies have been performed for cattle breeding. For instance,

after 10 days of aging, the steaks from an Angus breed were more