Pale, soft, and exudative (PSE) meat has been recognized for decades. Fast glycolysis
during early post-mortem stage while the muscle temperature is still high is the cause
of PSE meat. To elucidate the molecular mechanism underlying this fast glycolysis
in muscle to become PSE meat, post-mortem ATP metabolism, fructose-2,6-diphosphate
content, and the activities of AMPK, glycogen phosphorylase, and pyruvate kinase were
examined in post-mortem muscle. Earlier and faster post-mortem AMPK activation was
responsible for the significantly lower pH and higher lactic acid accumulation (p<0.05)
seen in PSE muscle, which resulted in the occurrence of PSE meat. In muscle that became
PSE meat, AMPK was activated at 0 h post-mortem and reached maximal activation at
0.5 h post-mortem, whereas AMPK reached maximal activation at 1 h post-mortem in the
normal pork loin. Higher fructose-2,6-diphosphate content (p<0.05) was detected in
PSE muscle compared to normal muscle at early post-mortem stage. However, no difference
in the activities of glycogen phosphorylase and pyruvate kinase, rate-controlling
enzymes in glycogenolysis and glycolysis, respectively, was detected between PSE and
normal pork loins. Because fructose-2,6-diphosphate is a product of phosphofructokinase-2
(PFK-2), these data suggest that AMPK regulates post-mortem glycolysis through its
phosphorylation and activation of PFK-2, which then up-regulates the activity of phosphofructokinase-1
(PFK-1), a key rate-controlling enzyme in glycolysis. Early AMPK activation in PSE
muscle is associated with early consumption of ATP, because higher AMP and IMP contents
and lower ATP content were detected in PSE meat compared to normal meat. Other mechanisms
causing early AMPK activation in PSE meat may exist, which warrants further investigation.