Analyse des allergènes alimentaires - Entre fiction et réalité (3)

La présence d’allergènes non mentionnés dans les aliments constitue un problème sanitaire important pour les personnes allergiques. Afin de répondre aux exigences légales, les fabricants doivent mettre en place des plans de gestion des allergènes définissant les points critiques à maîtriser, ainsi que la méthode d’analyse requise. À l’instar des kits ELISA, les kits PCR (réaction en chaîne par polymérase) disponibles à la vente reposent sur une technologie plus moderne. Mais peut-on pour autant supposer qu’ils constituent la meilleure option ?

Ce troisième article de notre série sur l’analyse des allergènes alimentaires est consacré à cette méthode d’analyse spécifique et aux idées reçues fausses la concernant.

PCR is more reliable than immunological tests

PCR is a complex method in which DNA is extracted from a sample. Specially designed primers anneal to a target fragment of the DNA that is specific for a certain species. Then the polymerase chain reaction takes place, whereby the target DNA is multiplied by a factor of 100 million to 1 billion. Upon addition of a dye, the target DNA fragment can then easily be detected.  

A method offering many advantages…  

This amplification process makes the method extremely sensitive and therefore attractive for use in cases of low level allergen contaminations. Furthermore, DNA is a remarkably stable molecule that remains unaffected by most of the common food processing methods. PCR is a highly specific method, meaning that it is able to overcome any cross-reactivity issue where other methods might fail.
Celery is an example of the need for specificity. To date, no antibodies have been developed that can reliably detect celery without also giving a signal to related species, such as fennel, carrot or parsley. Hence, celery detection with an immunological test is currently not possible.  

… but also disadvantages  

Performing a PCR is difficult, compared to an ELISA. Sample preparation and result interpretation are complex and require specially trained personnel.
The analytical target also possesses one fundamental drawback: the DNA molecule itself is not responsible for the allergic reaction. So the presence of the DNA is only an indicator of the allergenic potential of the sample. In addition, there are commodities that contain a lot of proteins, but very little to almost no DNA. And in some instances, DNA and proteins are separated as a consequence of food processing. Furthermore, it is not possible to distinguish between allergens (e.g. milk and egg) and tissue (e.g. beef or chicken meat) as a PCR test will only detect the presence of cow or chicken DNA.  

So, are immunological tests the better choice after all?  

It is hard to conclude which method is “better”. ELISA or lateral flow methods are well-established, while PCR kits for food allergen detection are relatively new.
Immunological rapid tests are still the gold standard and should be preferred in most cases as they directly detect food allergens. However, in some cases, PCR is a great alternative.    

In our next issue of “Food Allergen Testing – Facts vs. Fiction” we will discuss the common misconception that rapid tests are less accurate than mass spectrometry. Stay tuned.

 

This article  was originally published in "International Food & Meat Topics", Volume 28 Number 3 (2017)