PCR techniques on PAPs

Gilbert Berben
CRA-W, Gembloux (Belgium)


After a brief reminder of what is the principle of the Polymerase Chain Reaction (PCR), the lecture is focusing on its use for detection of processed animal proteins (PAPs) in feed or in feedingstuffs. As analytical technique, PCR is able to detect very specific pieces of nucleic acids. Therefore, it should be stressed that its use for the purpose of PAP detection is only an indirect method because the analyte considered is not a protein.

However, DNA has the advantage of being a rather resistant molecule that is a very good specific marker. PAP samples generally still contain enough DNA for its detection. All depends in fact on the strength of the heating process used during the rendering. That will inevitably lead to some break down of the DNA in smaller pieces. Consequently, PCR assays have to be designed in order to detect small enough targets (preferably less than 100 bp) which should moreover be present in sufficient copy number per cell (e.g. mitochondrial DNA targets).

Compared to other PAP detection methods, PCR has the major advantage of being able to assign a defined animal taxon to a target and this even at the level of the animal species. On the other hand, one of the drawbacks of PCR is linked to the fact that authorized feed ingredients (e.g. milk products) may also be sources of animal DNA. So, this can lead to interferences in the results and that is why one should be careful in their interpretation. It explains that in this kind of issue, generally PCR should be used in association with other techniques.

Finally, the lecture will highlight two very practical aspects when using PCR in routine applications: the question of the transferability of the technique and the fact that, unless with use of very specific units, the technique is merely qualitative and not quantitative as long as detection of PAPs is concerned.

Keywords :
Animal species identification, authorized feed ingredients, indirect method, PCR, processed animal proteins