Project title:    Airborne contamination in slaughterhouses

Duration:         1st August 2003 to 31st March 2005

Background and objectives

This study sought to identify whether aerosol movements are significant routes of carcass contamination in meat processing plants.  A secondary objective was to define affordable methods of reducing the contamination risk.

Approach

A new approach was devised to assess the role of aerosols in contamination of beef, lamb and poultry.  The microbial load on carcasses was measured after carcasses had been exposed along the slaughter line to normal factory air or to ultraclean air provided by a unit incorporating a high efficiency particulate air (HEPA) filter.  The airborne route would be shown to be important if the change in air quality had a significant effect on the microbial load on the carcasses.  The use of ultra-clean air was not proposed as a practical method of reducing airborne contamination, but solely to provide an experimental approach. In addition, for beef and lamb, replica carcasses with settle plates attached to them would also be exposed to factory air or ultra-clean air.  The results from these tests would be expected to show lower counts, because surface contacts, from items such as knives or workers’ hands, would have been eliminated.

Results

Tests in a chicken evisceration room showed conclusively that the airborne route contributes to the contamination of surfaces (p<0.001).  The concentration of microorganisms in the air and on settle plates was significantly reduced by the use of the HEPA unit (Figure 1).  However, the microbial counts on the carcasses were so high when they entered the room that the increase in microbial counts from airborne contamination was relatively very small.  In cattle slaughterhouses, the greatest airborne contamination occurs at the hide puller (p=0.008).  The use of ultra-clean air reduced the rate of deposition onto the settle plates (p=0.008), showing that the airborne route contributes to contamination, but other vectors of contamination of the brisket were even more important (Figure 2).  The brisket becomes contaminated prior to the hide puller because knives transfer contamination from the hide to the flesh.  The use of ultra-clean air when the brisket was first exposed showed that the airborne route was important (p=0.081), but it was not the greatest vector of contamination.  In lamb slaughterhouses, the greatest airborne contamination occurs at the fleece puller (p<0.05); however, the airborne route is not the greatest vector of contamination: the fleece, knives, and hands and arms of operators all contacted exposed flesh.

Significance

The airborne route is not the major cause of red meat carcass contamination so the emphasis should be on reducing the transfer of contamination by surface contacts from the hide/fleece.  This could include consideration of the type of hide puller and particular working practices. 

The main contamination of poultry carcasses occurs prior to evisceration and further work is being carried out in defeathering rooms.

Further information can be obtained by contacting the research team who undertook these studies.