Glycolytic potential and activity of adenosine monophosphate kinase (AMPK), glycogen phosphorylase (GP) and glycogen debranching enzyme (GDE) in steer carcasses with normal (< 5.8) or high (> 5.9) 24 h pH determined in M. longissimus dorsi

•Low LD muscle glycogen concentration is not the only factor determining high 24 h pH in steers.•GP activity postmortem increases in LD muscle with normal but not with high final pH.•AMPK activity postmortem is higher in LD muscle with normal vs high final pH.

Muscle glycogen concentration (MGC) and lactate (LA), activity of glycogen debranching enzyme (GDE), glycogen phosphorylase (GP) and adenosine monophosphate kinase (AMPK) were determined at 0.5 h (T0) and 24 h (T24) post-mortem in Longissimus dorsi samples from 38 steers that produced high pH (> 5.9) and normal pH (< 5.8) carcasses at 24 h postmortem. MGC, LA and glycolytic potential were higher (P < 0.05) in normal pH carcasses. GDE activity was similar (P > 0.05) in both pH categories. GP activity increased between T0 and T24 only in normal pH carcasses. AMPK activity was four times higher in normal pH v/s high pH carcasses, without changing its activity over time. Results reinforce the idea that differences in postmortem glycogenolytic/glycolytic flow in L. dorsi of steers showing normal v/s high muscle pH at 24 h, could be explained not only by the higher initial MGC in normal pH carcasses, but also by a high and sustained activity of AMPK and an increased GP activity at 24 h postmortem.