Evaluation of the pH Fall in English Lamb Abattoirs

Project number:                    73503

Lead contractor:                   EBLEX

Start & end date:                   Jan 2009 – July 2009

Actual end date:                    October 2011

 

The Problem:

It has long been understood that there are two types of muscle shortening resulting in toughness and that these can be monitored by observations of pH/temperature changes with time.  Under standard processing conditions pH is assumed to fall in a fairly consistent manner.  It is therefore generally adequate to monitor temperature change with time as a means of ensuring that rigor mortis occurs at an appropriate temperature to avoid excessive shortening.  This has been expressed as the “10 in 10 rule.  Developments in abattoir practice, however, mean that a standard pH decline can no longer be assumed.  In particular the introduction of electrical stimulation to enhance tenderness and other electrical inputs on the slaughterline increase the rate at which rigor occurs.  This means that the simple rule is no longer appropriate and increases the risk of hot shortening.

Evaluation of the pH/temperature relationship in beef plants in England and Wales carried out by EBLEX staff demonstrated that both hot and cold shortening is occurring in commercial beef slaughtering facilities.  It is likely that the control of the pH/temperature relationship in sheep plants has also diverged from best practice over time.

The most clear guidelines currently available on the target pH temperature relationship post slaughter for sheep, come from work jointly funded by the Australian Sheep Industry Cooperative Research Centre and Meat and Livestock Australia.

 

Project Aims:

To evaluate the pH / temperature relationship in lamb slaughter plants in England in comparison with published guidelines.

 

Approach:

Temperature and pH were monitored following slaughter in five lamb plants in England.  The results have been compared with the published guidelines.

 

Results:

No electrical stimulation

  1. Causes for variation in chilling rate in the same plant are not clear, although partly the result of differences in environmental temperatures.  This variation leads to variation in the risk of cold shortening.
  2. There was a risk of cold shortening, indicated by a pH of 6 or more at a temperature of 18ºC, in a number of carcases, and this varied by day, but in no plant was there a severe risk of cold shortening (pH of 6 or more at a temperature of 8ºC).
  3. Following the MLC recommendation of ensuring that no muscle should fall below 10ºC within 10 hours of slaughter would be a good basic measure to reduce the risk of cold shortening.  Cold shortening conditions only occur in a proportion of carcases, however, so      it is necessary to monitor temperature in a wide sample of carcases.

High voltage electrical stimulation

  1. The electrical stimulation was highly effective in reducing pH and no carcases had a pH of more than 6 by the time a temperature of 18ºC was achieved, indicating no risk of cold shortening.
  2. The pH fall in a high proportion of carcases was too rapid, resulting in a pH of less than 6 while the temperature was at 35ºC or above.  This indicates that hot shortening is likely to be occurring, particularly in the more difficult to cool muscles of the leg.
  3. MLC guidelines for chilling rate do not take account of the risk of hot shortening and the introduction of an MSA-style pH-temperature window would provide industry with a useful guide.
  4. Chilling rate could be more rapid (in the light of the fact that ES is in use) to reduce drip loss and the risk of hot shortening.
  5. Measurement of pH immediately post-stimulation is insufficient to detect hot shortening and more detailed monitoring is required to establish the best time for routine measurement in the specific circumstances.
Overall
  1. Ultimate pH was normal where it was measured.
  2. Carcase chilling is affected by the carcase weight such that the risk of cold shortening is lower in heavier carcases.
  3. Chilling conditions should be targetted to meet carcase characteristics where possible.
  4. Effective monitoring of pH in a sample of carcases is a useful tool to improving consistency in meat quality, through reducing the risk of shortening.

 

Planned activity:

  • A press release on the results.
  • A guide for measuring pH in lamb.