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Physico-chemical changes during the conversion of muscle to meat in post-mortem period

Next we are going to move on to what happens to muscle pH after slaughter. The drop of pH as well as the ultimate pH has a very big effect on the colour, texture and water holding capacity of the meat.

Why not take a few minutes see what you already know by completing these pre-section questions?

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1

After slaughter, as O2 supply falls, energy levels in the form of ATP decrease.

a)
b)
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2

Low pH prevents or retards microbial growth.

a)
b)
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Pre-slaughter

In the living animal, aerobic metabolism is used to obtain energy. However, under stressful situations, anaerobic metabolism may be used and lactic acid is produced. Lactic acid is usually transported from the muscles to the liver, where it is re-synthesized into glucose and glycogen, or to the heart, where it is metabolized to carbon dioxide and water.

Post slaughter

After slaughter, aerobic metabolism begins to fail due to the stored oxygen supply being depleted. To maintain homeostasis, anaerobic energy metabolism starts producing lactic acid, consuming the glycogen stored in the muscles. Thus, the structural integrity of the cells is maintained for a period of time although less energy in the form of ATP is produced.

In the exsanguinated animal, the circulatory system is not capable of removing metabolites so that lactic acid remains in the muscle and increases its concentration during the post-mortem period until the glycogen stored in muscle is consumed.

The drop in pH and the ultimate pH of muscle will be different depending on the type of muscle metabolism (glycolitic and oxidative muscles).

  • Glycolitic muscles produce higher amounts of lactic acid than oxidative ones because they use the glycolitic pathway to produce energy rather than the oxidative pathway. For instance, in Semimembranosus, Longissimus dorsi and Biceps femoris, the pH declines quicker and to a greater extent than other muscles such as Semispinalis capitis, Psoas major, Serratus ventralis and Quadriceps femoris.