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pH changes: PSE Meat

As we have seen in the last graph, different meat quality levels could be defined depending on the pH drop during the post-mortem period.

Before you begin to explore PSE meat, let's see what you already know:

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1

The PSE meat is caused by a fast decrease of the muscle pH.

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In some animals, muscle pH drops rapidly below 5.80 during the first hour after exsanguination to the ultimate pH. This kind of meat is termed Pale, Soft and Exudative (PSE). The low pH prevents or retards microbial growth. The rate of pH change post mortem also influences meat quality.

Development of a low pH (acid) in muscle causes denaturisation of muscle proteins. This denaturisation causes:

  • loss of protein solubility
  • loss of water- and protein-binding capacity
  • loss in intensity of muscle pigment colouration

All these changes are undesirable, whether the muscle is going to be used as fresh meat or subjected to further processing.

The gene that is responsible for PSE meat is the Halothane sensitivity gene (HAL), which is associated with a fast rate of post-mortem decline in pH and which is more likely in stress-susceptible animals. Halothane positive animals are homozygous, and they can be detected by exposure to halothane gas, which induces the Porcine Stress Syndrome (PSS). However, a more accurate identification of three genotypes is now possible using a direct marker test (DNA Test) developed after the identification of the gene (ryadonine receptor gene, RYR1) and the discovery of the specific mutation.

The pig is not the only animal that can be affected by this kind of defect. Pale meat or exudative meat can be also detected in beef and poultry, but are not necessarily undesirable attributes in these species.

Although it is not frequent, exudative meat has been found in carcasses of young bulls. The deviation in quality is generally much less pronounced than that of PSE pork, so that PSE in beef has been little investigated.

In poultry, particularly turkey, it is common to find pale meat but it is not exudative. Usually it is related to a low haem pigment content of the muscle.