Effects of sugars on post-mortem glycolysis in bovine muscle mince

Sternomandibularis muscles from steers were minced, within 75 min of slaughter, with sugars or amylases. The minces were held anoxically at 25°C for at least 7 h. At times samples were removed and chemically analysed. Glucose (1·5%) retarded the post-mortem pH fall, with kinetics similar to those of NaCl (2·0%). Typically, 1·5% glucose maintained the pH at 6·1, whereas control mince attained 5·5. Lesser amounts of glucose had a reduced effect. Other sugars were inactive. The metabolic effects of 1·5% added-glucose were compared with those of an iso-osmotic control, 1·5% added-fructose. For the glucose mince there was no change in glucose concentration over 7 h suggesting that the endogenous hexokinase was inactive. Further, more glycogen remained in the glucose mince that in the control, indicating that glucose inhibited glycolysis. This was confirmed by electron microscopy and was reflected in pH and lactate levels. Hexose monophosphates were strongly affected by glucose. In the control, their concentrations each fell in the first 2 h then increased steadily, as expected. In the presence of glucose, their concentrations were initially lower and decreased steadily with time. Concentrations of adenosine phosphates were little affected by glucose, but downstream products of purine metabolism showed marked differences, probably due to enhanced nucleotidase activity above pH 6. Glucose plus yeast hexokinase produced a mince with a rigor pH close to normal. The data indicated that phosphorylase activity was inhibited by glucose, and suggested that glucose was not phosphorylated because of muscle hexokinase inhibitors such as glucose-1,6-diphosphate.