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Health Protection Service – Microbiological quality of kebabs

Microbiological quality of kebabs

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Objective

• To determine the microbiological status of kebabs in the ACT to ensure their safety.
• Determine the current range of food handling practices in the kebab industry and to establish whether or not pathogens can be transmitted via kebab meat.

Background

Kebabs are a traditional Middle Eastern meat dish made by stacking layers of meat such as chicken, beef or lamb, which is seasoned, marinated and sliced or minced, onto a vertical skewer to form a cone or cylinder shape. The skewer rotates in front of a vertical heat source and as the outer layer of meat is cooked, it is carved off in slices. The meat is then served in flat bread together with salads and dips.

Kebabs are a very popular type of convenience take away food. The preparation and cooking practices of kebabs have the potential to allow the consumption of undercooked meat that may harbour pathogenic bacteria.

Following a number of cases of illness that had circumstantial links to the consumption of kebabs1, a survey was conducted to assess the microbiological safety and quality of cooked kebab meat (chicken, lamb and beef) from vertical spits. Environmental Health Officers randomly selected and sampled businesses selling meat cooked on a vertical rotating spit.

Survey

This survey was conducted between the 03 July 2002 and 27 November 2002. During this period samples from a range of ACT retail outlets were collected randomly by Environmental Health Officers (EHO) and processed by the Microbiology Unit of ACTGAL.

Standards

Kebabs have been categorised as a ready-to-eat food. The Food Standard Australia New Zealand (FSANZ) Draft Guidelines for the Microbiological Examination (RTE) Foods are shown in Table 1 are applicable to this food.

Table 1 Microbiological Examination (RTE) Foods

 

cfu/g = colony forming units per gram of material analysed.
# Pathogenic strains of E. coli should be absent.
* Foods with a long shelf life stored under refrigeration should have no L. monocytogenes detected in 25g.
** The detection of L. monocytogenes in ready-to-eat foods prepared specifically for “at risk” population groups (the elderly, immuno-compromised and infants) should also be considered as potentially hazardous.

Results

A total of 82 samples of whole kebabs were tested for the organisms listed in Table 1. Samples consisted of 36 chicken, 20 lamb, 22 beef and 4 vegetarian Kebabs. Results of the survey are tabulated in Table 2 below.

Table 2 Results of the survey

 

NA= Not applicable.
*expressed as colony forming units per gram.

Escherichia coli
82.3% of the samples showed a satisfactory microbiological quality. E. coli was detected in 14 of the 79 samples tested. 15.2% of samples were marginal and 2.5% were categorised as unsatisfactory. The positive results isolated ranged from 7-460 colony forming units/gram (cfu/g). The vegetarian kebab had the maximum 460 cfu/g E. coli present. No re-samples were requested for the results, which fell into either the marginal or the unsatisfactory category.

The presence of E. coli is undesirable because it is indicative of poor hygiene conditions, which have lead to contamination or inadequate heat treatment. Ideally E. coli should not be detected and as such a level of <3 cfu/g has been given as the satisfactory criteria for this organism. Levels exceeding 100 cfu/g are unacceptable and indicate a level of contamination, which may have introduced pathogens or that pathogens, if present in the kebabs prior to processing, may have survived.

Coagulase positive Staphylococci
Coagulase positive Staphylococci were detected in only 8 (10.1%) of the tested samples. 89.9% of the samples were free of coagulase positive staphylococci indicating good microbiological quality. The highest coagulase positive Staphylococci contamination was found to be 450 cfu/g. This particular sample was also contaminated with E. coli. None of the samples, which tested positive for coagulase positive Staphylococci, exceeded 1000 cfu/g and thus were found to be compliant with the Guidelines. No resample was requested for the results falling in the “marginal” category. Contamination of kebabs with coagulase-positive Staphylococci is largely as a result of human contact. Contamination should be minimised through good food handling practices and growth of the organism prevented through adequate temperature controls.

Salmonella spp.
No Salmonella was isolated from any of the kebab samples in this study. The results indicate that 100% of the samples were satisfactory and of good microbiological quality.

Listeria monocytogenes
Listeria monocytogenes was isolated from 10 (12.2%) samples categorising these as marginal. 87.8% of the samples tested were satisfactory. Three of the samples positive for Listeria monocytogenes were also positive for E. coli. These results indicate that this sample may have been cross-contaminated due to unhygienic conditions. According to the FSANZ Guidelines, no Listeria monocytogenes should be detected in the sample to pass the satisfactory criterion. Re-samples were requested for all samples in which Listeria monocytogenes was isolated. Only one sample was received and re-sampled. A semi-quantitatively analysis of the re-sample was undertaken with L. monocytogenes isolated at a range of 1-10 organisms per gram.

Higher levels of L. monocytogenes (>100 cfu/g) definitely indicate a failure with food handling controls and based on current epidemiological evidence are considered a public health risk.

Clostridium perfringens
No Clostridium perfringens was isolated from any of the kebab samples in this study. 100% of the samples indicated good microbiological quality.

Figure 2 below, shows the microbiological quality of kebabs tested in this survey.

Figure 2 Microbiological quality of kebabs

 

Discussion

Overall the standard of microbiological quality of kebabs is good. None of the 82 samples tested contained Salmonella spp. or Clostridium perfringens. Only 2 samples were unsatisfactory as they contained 100 cfu/g of E. coli. Results outside of acceptable microbiological limits are indicative of poor hygiene or food handling practices. Listeria monocytogenes was detected in 10 samples categorising them as marginal. 12 samples containing E. coli were also marginal in their microbiological quality. Marginal results are borderline in that they are within limits of acceptable microbiological quality but may indicate possible hygiene problems in the preparation of food.

The way the kebab rotating spit is designed where the meat cooks from the outside to the inside, even when the surface temperature may be above 75C, means the internal temperature of the meat could potentially be in the danger zone of 5-60C. This temperature zone could provide an ideal temperature for the pathogenic bacteria to multiply. Even if the surface temperature is high enough to destroy food poisoning bacteria, the meat can still be cross-contaminated during slicing by fluids draining from the inside of the vertical raw meat skewer.

Results of this survey indicate that there is evidence that inadequate cooking temperatures/ times and/ or cross contamination of kebabs was occurring due to improper or unhygienic handling of the food. Use of a second cook step to further cook the sliced meat prior to serving would help destroy bacteria that could have survived the initial cooking step.

Re-samples

Health Protection Services (HPS) Sampling Working Group needs to evaluate its re-sampling protocol for future surveys. Re-sampling should be requested when a sample fails to meet the acceptable microbiological standard. Presently re-samples are requested only when Listeria monocytogenes or Salmonella spp. is isolated. Re-samples need to be also requested for other microbiological bacteria isolated at Unsatisfactory levels.

Conclusion

Overall, the microbiological quality of kebabs sold in the ACT is good. However poor processing hygiene can give unsatisfactory or marginal results, which are not compliant to the FSANZ Guidelines. For the premises that gave unsatisfactory results further sampling and investigation should be undertaken to determine whether food handling controls and hygiene practices are adequate.

Recommendation

• That a future survey be conducted to confirm the proper handling / processing of the product is occurring.
• Retailers are educated in proper handling practises as per FSANZ Foods Safety Standards.
• Investigate the option of introducing a second heat treatment step to ensure product is adequately cooked.
• Undertake re-sampling and investigation of premises with unsatisfactory results.

Bibliography

1 Report on Microbiological Survey of Kebabs – Food Safety Victoria 2002
2 Guidelines for the Microbiological Examination of Ready-to-eat-Foods (December 2001)

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