Testing for horse DNA in beef food samples

Is the beef in your ready meals really beef? The current scandal in Europe is resulting in a scramble from food processors to check that their beef isn’t actually horse.

European Union ministers have called in Europe’s law enforcement agency to help tackle the spreading crisis over mislabelled frozen meals containing horsemeat and promised rapid DNA food testing in an effort to restore consumer confidence. The European Health Commissioner Tonio Borg said the EU was calling on all 27 member states to carry out DNA tests on beef products to see if they contained horse meat.

Testing

There are two methods used to detect different species of meat within a food sample (for example testing for horsemeat in a beef lasagne). The first is ELISA (looking for animal protein) and the second is PCR (detecting animal DNA).

ELISA

ELISA has a lower detection limit and requires different test kits depending on the species and whether the meat is cooked or raw. In the current food crisis this information is not readily available because the exact source of contamination is unknown. Therefore, DNA testing with a superior detection limit and almost 100% specificity and sensitivity is the most suitable method.

PCR

Polymerase chain reaction utilises short sections of DNA called primers specific to beef and horse. In the experiment, these primers bind to the animal DNA in the sample and allow the animal DNA to be copied millions of times until there is sufficient material to be visualised and compared to known standards.

Test procedure

1. Prepare the sample. Mix the food sample (eg, beef lasagne) thoroughly in a blender/stomacher to evenly distribute any DNA contamination.
2. Extract the DNA. Careful preparation of the sample is performed by experts in a laboratory by diluting, washing and centrifugation of the DNA.
3. PCR analysis. DNA from the prepared sample is amplified in a thermal cycler using nuclease-free water, the enzyme Taq DNA polymerase, dNTPs, MgCL2, reaction buffers and animal-specific primers. The thermal cycler treats the mixture to 35 cycles of:
   a. 94°C for 30 s
   b. 60°C for 30 s
   c. 72°C for 1 min
4. Separation of DNA - the amplified DNA is stained and separated by size into distinct bands using a widely used technique, agarose gel electrophoresis.
5. Results analysis - the resulting gel is placed into a gel documentation system which takes an image. The operator can then compare the sample DNA against known standards. This indicates with a high level of certainty whether the sample contains horse or beef DNA.