On 15 January, four major UK supermarkets withdrew meat-based products in the light of the Food Standards Agency Ireland (FSAI) findings into the contamination of beef with horse and other animal meats.
The highest content of equine DNA was 29% in one sample, with the vast majority of others tested below <0.2%. Many samples were also found to contain porcine DNA.
The scandal has resulted in one of the biggest food recalls in UK history, and multiple suppliers across the EU being implicated. To deal with the growing scandal over mislabelled horse-meat, the EU Health Commissioner today urged all members to carry out DNA tests on processed beef for traces of horse-meat for three months from 1 March. Furthermore, tests for the presence of the veterinary medicine phenylbutazone ("bute") were recommended.
We thought it may be interesting to look at some of the scientific challenges in authenticating presence of animal species in our meat. What types of horse-meat tests are out there? Further, how accurate are current tests in quantifying horse DNA? In fact, one food testing company in the UK this week has urged the food testing industry to not rush into horse DNA testing due to issues surrounding DNA quantification.
Currently, in the food testing industry there exist two main types of assays for detecting horse meat in beef – either protein-based or DNA-based.
The ELISA method tests for protein and has a 1-2% detection limit. Separate kits exist for testing either raw or cooked meat. However, due to the contamination being largely unknown, the ELISA method could possibly show inaccurate results.
With molecular-based testing of equine DNA using PCR, the detection limit is 1% but the limit of detection (i.e. sensitivity) can go down even lower. Both real-time PCR methods and end-point PCR (with subsequent RFLP analysis or sequencing) are suitable for DNA testing of equine DNA. PCR based methods amplify sequences from mitochondrial DNA (mtDNA) which is more highly conserved and widely found in animal species than nuclear DNA. Specific details of primer sequences are not always made available by different companies.
Due to the wide variation in the amount of mitochondria from cell to cell in different tissue types (varying from 1 mitochondria per cell to 1000’s), it is not possible to accurately quantify the amount of horse DNA in a sample. DNA testing therefore should be seen as being qualitative rather than quantitative, and limitations to their accuracy should be borne in mind when interpreting results or those quoted in the press.
Bioline high performance molecular biology products have been cited in recent papers investigating contamination of meat products by horse meat, as well as other types of contaminants detected in food-testing.
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