Testing of environmental and food contact surfaces

Background:

From January 1st 2006 there was no longer a statutory requirement for plant operators to routinely test their environmental and food-contact surfaces microbiologically. This requirement was replaced with a legal requirement to undertake environmental testing “when necessary to ensure the criteria are met” which means it should be considered as part of validation of cleaning and in “corrective actions” when investigating reasons why carcass or processed meat test results have increased . Plants should use ISO standard 18593 as the reference method for sampling processing areas and equipment or a suitable alternative method therefore plants may be interested in a number of alternative rapid methods that have been reviewed favourably as part of a recent FSA-funded study (MO1020).  These alternative rapid methods can offer advantages over traditional microbiological testing including cost savings and providing almost-instant results.  Many plants will continue to test their surfaces routinely for total aerobes to comply with their customer protocols and to ensure that cleaning has been undertaken to an acceptable standard.

The edited highlights:

• The results of the study indicated that the VerifEYE Solo is a good method to measure overall carcass contamination for cattle and sheep carcasses.  The VerifEYE is not suited for assessing pig carcasses or the cleanliness of environmental surfaces.

• Assessment of environmental surface cleanliness in red meat abattoirs was most cost-effectively achieved using either the Pro-tect or the Flash stick detection system.  Two ATP detection systems were also assessed favourably, but ATP is a more expensive system for meat plants to adopt.

A more-complete project summary:

 The performance of rapid methods, alternative to the traditional microbial detection methods for monitoring hygiene in red meat abattoirs, was assessed both under experimental (laboratory and abattoir) and commercial conditions.  The methods assessed were based on the detection of protein residues (using the commercially-available products "Pro-tect" [photograph 1] and "Flash sticks" [photograph 2]), total ATP (the Lightning II and Hygiena Snapshot swabs [photograph 3]) and porphoryn (a chlorophyll derivative present in the faecal material of animals fed on a diet rich in plant material; detected using a hand-held VerifEYE Solo). Microbiological testing (total aerobic viable counts; TVC and Enterobacteriaceae) was also carried out on the carcasses and surfaces to provide a general background of hygiene against which the performance of the test methods could be assessed.

Photograph 1: The liquid in the left side of the Pro-tect swabs changes colour from green to purple dependent on the concentration of protein residue on an environmental surface

Photograph 2: The pad on the end of a Flash stick changes from yellow to blue when exposed to protein residues on an environmental surface

Photographs 3A and 3B: ATP detection involves the the use of a luminometer to measure how much light is produced from the contamination present on an environmental surface

An initial lab-based investigation was undertaken to assess each of the alternative methods under controlled conditions, and to identify any potential problems with the practical use of these methods. The VerifEYE Solo was found to be easy to operate.  Optimal performance was observed at a distance of 16mm from the target surface. A range of surfaces found commonly within the abattoir were assessed for the ability to fluoresce as fluorescence can interfere with the detection of faeces by the machine.  Objects such as abattoir wall cladding were found to fluoresce, and the background colour of the surface was shown to have an effect on the reading obtained by the VerifEYE Solo. Diluted faeces were more readily detected than faecal smears, particularly when the faecal smears had dried. Faecal spots as small as 0.3mm could be detected using the system.  However, pig faeces, sourced from a number of different farms, did not fluoresce under the VerifEYE Solo system

The performance of the same detection methods were assessed at Bristol University experimental abattoir during normal processing conditions.  Chlorophyll solutions were used to assess the practical effectiveness of the VerifEYE system.  Chlorophyll “contamination” was tracked from the hides/fleece/skin of the cattle, sheep and pigs, to the resulting carcasses.  TVC and numbers of Enterobacteriaceae were also determined from the coats and carcasses of the animals.  Surfaces within the abattoir were also monitored using each of the different methods, including the traditional microbiological tests, both before and after routine cleaning.   A correlation between the total ATP and both protein detection methods was observed from the environmental surfaces associated with slaughter of all three animal species.  A correlation was also observed between the total ATP, Flash protein method and the TVC counts with the surfaces related to cattle slaughter.  Transfer of bacteria from the coat/skin of the animal to the carcass was similar in the animals as the transfer of chlorophyll.  Transference of bacteria from coat to carcass was lowest for sheep when compared with the other two species. These findings are strongly indicative that monitoring of the transfer of bacteria to the carcass gives a good indication of the cleanliness of the dressing procedure for red meat animals. Under controlled conditions in a laboratory or experimental red meat plant, the detection of porphoryn (faeces) on sheep and cattle carcasses using the VerifEYE Solo and the detection of protein and total ATP on environmental surfaces were assessed favourably as monitors of process hygiene in red meat abattoirs

 The final assessments were undertaken to examine the performance of the test methods on carcasses (cattle and sheep only) and surfaces (cattle, sheep and pigs) within commercial abattoirs. In order to carry these out, three commercial abattoirs were visited and carcasses sampled on four sites immediately prior to chilling. The surfaces were assessed both before and after routine cleaning. Assessment of the sheep carcasses indicated a potential correlation between the Enterobacteriaceae count and the VerifEYE Solo readings as both methods indicated the brisket area on the carcass to be the most frequently contaminated. No such correlation was observed when the data from the cattle carcasses was examined. The VerifEYE Solo readings from the carcasses were found to give a good overall indication of process hygiene as a whole with both cattle and sheep carcasses, but did give an indication as a potential use for assessing faecal contamination at individual sites for sheep carcasses

Analysis of the abattoir surface data indicated that the VerifEYE Solo did not detect significant levels of faecal contamination and therefore was not well suited to assessing the hygiene of surfaces. However, the other methods tested did show some strong relationships between each other when used to determine cleanliness of the surfaces, particularly in the sheep and pig plants. Both protein detection methods used were able to detect that effective cleaning had taken place within the abattoirs, but it was felt that the Flash protein method would be better suited to the abattoir environment. Although more expensive, the measurement of total ATP to determine surface cleanliness was also thought to be a useful method within the abattoir to assess surface cleanliness

Overall, the results of these studies have indicated that the use of the VerifEYE Solo is a good method to measure overall carcass contamination within red meat abattoirs for cattle and sheep but has limited use for assessing surface cleanliness.  The assessment of surface cleanliness in red meat abattoirs for all red meat species, was most cost-effectively achieved using either of the protein detection methods assessed.

Supplier's web addresses for the rapid testing systems that were assessed*

*The Food Standards Agency provides these suppliers’ details only for the convenience of plant operators.  The Agency neither recommends nor endorses these companies or their products.  There are a large number of commercially-available protein residue and ATP detection systems.  It is likely the vast majority of these systems are suitable for use within meat processing plants.

Pro-tect swab-based protein residues detection from Biotrace International Plc

Flash stick-based protein residues detection from Biocontrol

Lightning 2 MVP ATP Detection system from Biocontrol

Snapshot ATP Detection system from Hygiena International