pH inactivation of phosphofructokinase arrests postmortem glycolysis

Fresh meat quality development is influenced by pH decline that results from muscle glycolyzing energy substrates postmortem. The exact reason why glycolysis stops in the presence of residual glycogen remains unclear. We hypothesized that a critical glycolytic enzyme loses activity near the ultimate pH of meat. Porcine longissimus muscle samples were subjected to an in vitro system that mimics postmortem anaerobic metabolism at buffered pH values (7.0, 6.5, 6.0, 5.5 or 5.0). At pH7.0, 6.5, and 6.0, glycogenolysis and glycolysis proceeded normally while pH5.5 stopped lactate formation. Additional experimentation indicated that phosphofructokinase lost activity at pH5.5 while all other glycolytic enzymes remained active. A similar inactivation of phosphofructokinase was observed when using chicken and beef muscle. Elevated temperature hastened pH decline and phosphofructokinase activity loss. Thus, pH inactivates phosphofructokinase and arrests postmortem glycolysis, which may explain the similar ultimate pH across meat of different species.