The eight major foods linked to allergies are peanut and tree nut, milk, egg, soy, wheat, fish and shellfish. Such allergens can be detected using a variety of methods, however, this article compares ELISA to mass spectrometry.
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While foods containing the above eight ingredients need to be labeled in certain countries, this is only required if these are added intentionally. Therefore, this means that traces which could have come from other food items being prepared in the same factory may be present in foods which are made without these ingredients, e.g. due to shared surfaces. Consequently, there is a need for food allergen detection.
Why is it important to test food for allergens?
Manufacturers do place “may contain…” advisory notices and one study found that 43% of chocolate with an advisory label showed traces of peanuts. However, the same study also showed that 25% of chocolate without an advisory label were found to contain peanuts.
A different study found that 75% of products with an advisory label showed traces of milk, while some other products without an advisory label (or with “dairy free” label) also showed traces of milk. This shows that, while these advisory labels are accurate in some instances, there are other cases where these are unnecessary.
Over-labelling with advisory notices has the potential to create a scenario whereby these are ignored. Hence, more accurate labeling would be preferred, which would stem from the accurate quantification of allergens.
How is the testing for food allergens done?
In Enzyme-Linked Immunosorbent Assay's (ELISAs), antibodies, an enzyme, and its substrate are used to detect proteins found in food which can be allergens to some people; i.e. proteins found in peanuts. There are variations in the ELISA methods which differ in the number of antibodies used and whether the target protein is “captured” first or not.
Once the antibodies have been added to the reaction and allowed to bind, the substrate for the enzyme linked to the last antibody is added. This results in a change which can be measured, and these measurements can be used to quantify the amount of target protein present in the food.
Mass Spectrometry is a technique which measures the different masses of molecules within a sample, including proteins. These molecules are initially vaporized and is then hit by electrons. This gives each molecule or fragments of molecules a charge; if electrons are lost from the molecule, the molecule becomes positively charged, while the addition of an electron to the molecule will result in a negative charge.
These ions are then sorted by charge and size according to how fast they travel, and also how much they are deflected by when a magnetic field is applied. Mass spectrometry can also be coupled to chromatography, such as liquid chromatography (LC-MS).
One big difference between ELISA and mass spectrometry is that ELISA detects the presence of proteins, while mass spectrometry detects the presence of peptides, which are fragments derived from proteins. ELISA is limited to the detection of one protein, while multiple peptides can be detected by mass spectrometry.
What are the advantages and disadvantages of each method?
It has been reported that ELISA is sensitive, and has the ability to detect allergens at levels of ~0.1 – 5mg kg-1. It is difficult, however, to know at what quantity the protein becomes an allergen, due to differences in individual reactions. Another advantage of ELISA is that it is relatively easy to use and there are readily available standards and validation tools.
A disadvantage of ELISA is that, if the target protein has been altered (perhaps by heating), then the antibodies used may no longer be able to recognize the target protein. This results in a false negative, which could have dangerous consequences for the consumer. Conversely, if the target protein is similar to other proteins found in food, an ELISA could report a false positive result as the allergen is not present.
Differences in preparing the food for testing may also affect the ELISA and thus the final results. Other disadvantages include the fact that different antibodies and standards can be used for the same target protein, which may lead to different results.
As mentioned before, mass spectrometry can detect multiple target peptides at once, while retaining the same level of sensitivity as ELISA. However, there can be some levels of assumption when quantifying peptides from mass spectrometry data, therefore this could be a disadvantage. Another advantage is that the structure of proteins is not important, as mass spectrometry looks at its peptides.
The main disadvantage of mass spectrometry is that if the starting material is highly complex, then the sensitivity may actually be impacted. This could potentially be overcome by first removing dominant proteins and peptides in order to look for other proteins which are not as dominant.