From muscle to meat
Glycolysis is one of the key metabolic pathways in the conversion of muscle to meat. In living tissue glycolysis helps generate adenosine triphosphate (ATP) for cellular functions. This includes muscle contraction and it also helps initiate relaxation; Ca2+ is removed from the sarcoplasm via ATP-dependent Ca2+ pump, thereby removing the ability of Ca2+ to induce and sustain contraction.
In post-mortem muscle, the tissue attempts to maintain homeostasis by preserving ATP concentration. However, due to circulation failure following exsanguination, muscle lacks the oxygen required for oxidative metabolism. Consequently, muscle glycogen is metabolized via anaerobic glycolysis, which is less efficient at generating ATP. Thus, as post-mortem metabolism continues, glycogen and ATP levels decline and lactic acid accumulates, lowering muscle pH. This process results in an overall pH decline to an ultimate pH (pHu) of about 5.4 to 5.7 at 24 hours after slaughter (Bowker et al., 2000).
Consider the physical effects of stress on livestock. How does pre-slaughter stress affect post-mortem muscle acidification?