Food Chemistry

588 12 Meat

Fig. 12.22. Post-mortem changes in beef muscle.
aM. longissimus dorsi;bM. psoas; ——: pH value;

• 
  
  
  
  • -: ATP as % of the total acid-soluble phosphate; -·-·-:
    creatine phosphate as % of the total acid soluble phos-
    phate. (according toHamm, 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 tis-
sue 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 re-
serves 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 mus-
cle 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. Fig-
ure 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 car-

cass 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 measure-

ment of the meat at 4 cm depth; bound water as percent

of total water; lactic acid results are on fresh weight ba-

sis and ATP expressed as percent of total nucleotides.

(according toDisneyet 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 un-

dergo extensive drip loss because of lowered wa-