ABSTRACT
After death, with the breakdown of glycogen and the formation of lactic acid (lactate), the pH within the cell falls from approximately pH 7 in the muscle of a rested animal to approximately pH 5.3-5.8. Th is ultimate pH is near the isoelectric point of meat proteins. Th ese chemical changes postmortem cause physical changes because the swelling of the myofi bers is reduced and is at a
Table 18.1 Water Distribution in Muscles of Live Animals (pH 7) and Meat (pH 5.3-5.8)
% Water
Muscle Meat
Protein-bound water ∼1 ∼1 Intrafi lamental ∼80 ∼75 Interfi brillar ∼15 ∼10 Extracellular water ∼5 ∼15
minimum at the isoelectric point (Figure 18.1). Also, the rigor mortis occurs after the exhaust of convertible energy in muscle cells postmortem with its permanent interaction of myosin and actin in the fi laments. Th is shrinkage, due to both events, means that less water is immobilized within the myofi bers, and by the shrinkage water appears slowly outside the cell. Approximately 15% of the water is located fi nally outside the muscle cells and kept within the meat by capillary force (extracellular water; Table 18.1). But slowly this water evaporates into the environment or is lost as drip loss.
