Experimental Prevention of Dark-Cutting Meat

Abstract

“DARK-CUTTING” meat commonly results when cattle are subjected to prolonged stress just prior to slaughter. Subcutaneous injections of epinephrine administered for 24 to 48 hr. prior to slaughter has been shown to mimic the condition produced by natural stress conditions. Epinephrine acts to accelerate glycogen metabolism in muscle tissue. Low muscle glycogen stores at slaughter preclude the development of a desirable pH after death. When muscle pH remains elevated in the carcass, mitochondrial respiration remains high and myoglobin is deoxygenated. A dark red color results. We have used propranolol, a beta-adrenergic blockade agent, and a competitive inhibitor of epinephrine to prevent the occurrence of “dark-cutting” carcasses in sheep. Sheep were injected (8.8 mg/ 100 kg) at 44, 24 and 16 hr. prior to slaughter. Propranolol was injected (110 mg or 200 mg/100 kg) simultaneously and at 48, 40 and 20 hr. prior to slaughter. Animals injected with epinephrine alone exhibited 48 hr. post-mortem pH averaging 6.6, “dark” meat, and depleted muscle glycogen at slaughter. Isolated mitochondria respired actively 48 hr. after slaughter. Sheep injected with epinephrine and with propranolol exhibited 48 hr. postmortem pH averaging 5.8, “normal” meat, and normal muscle glycogen content at slaughter. Isolated mitochondria respired at less than half the rate of mitochondria isolated from sheep injected with epinephrine alone. There were no significant differences in any parameter between control sheep and those injected with both epinephrine and propranolol.