2009_Book_FoodChemistry

588 12 Meat
Fig. 12.22. Post-mortem changes in beef muscle.
a M. longissimus dorsi; b M. psoas; ——: pH value;
- - -: ATP as % of the total acid-soluble phosphate; -·-·-:
creatine phosphate as % of the total acid soluble phosphate.
(according to Hamm, 1972)
Although muscle tissue is soft and flexible and
dry on the surface immediately following death,
its flexibility or extensibility is lost very rapidly.
ATP breaks down (Fig. 12.22). The muscle tissue
becomes stiff and rigid (death’s stiffening,
rigor mortis; cf. 12.3.2.1.5 and 12.3.2.1.6) and,
as the rigor proceeds, the muscle tissue surface
becomes wetter. The depletion of the energy reserves
results in the distribution of the calcium
ions, which are stored in the mitochondria and in
the sarcoplasmic reticulum, throughout the entire
intracellular matrix.
The onset of rigor mortis occurs in beef muscle
within 10–24 h; in pork, 4–18 h; and in
chicken, 2–4 h.
The rate of decrease in pH and the final pH value
of meat are of significance for water holding
capacity and, therefore, for meat quality. Figure
12.23 shows that a more rapid and intensive
Fig. 12.23. The effect of temperature on post mortem
changes in beef muscle.
M. semimembranosus : normal cooling, animal carcass
kept for the first hour post-mortem at 2–4 ◦ Cthen
posterior hind quarters cut and kept at 14 ◦ C for 10 h
followed by 2 ◦ C; : cooling in ice, hind quarters 11 h
in crushed ice, followed by 2 ◦ C. Temperature measurement
of the meat at 4 cm depth; bound water as percent
of total water; lactic acid results are on fresh weight basis
and ATP expressed as percent of total nucleotides.
(according to Disney et al., 1967)
cooling of the post mortem muscle results in
meat with a noticeably higher water holding
capacity than that of muscle cooled slowly.
12.4.2 Defects (PSE and DFD Meat)
Rapid drops in ATP and pH (Fig. 12.24) cause
pork muscle to become pale and soft and to undergo
extensive drip loss because of lowered wa-