ELISA versus Mass Spectrometry

While foods containing the above eight ingredients must be labeled in some countries, this is only required if they are intentionally added. Therefore, this means that traces that could have come from other foods prepared in the same factory may be present in foods that are made without these ingredients, e.g. due to shared surfaces. Therefore, there is a need for the detection of food allergens.

Why is it important to test foods for allergens?

Manufacturers place "may contain..." warning notices and one study found that 43% of chocolate with a warning label had traces of peanuts. However, the same study also showed that 25% of chocolate without a warning label contained peanuts.

Another study found that 75% of products with a warning label had traces of milk, while some other products without a warning label (or with a "dairy-free" label) also had traces of milk. This shows that while these warning labels are accurate in some cases, there are other cases where they are not necessary.

Excessive labeling with advisory notices can create a scenario where these are ignored. Thus, more accurate labeling would be preferred, which would derive from accurate quantification of allergens.

How is the food allergen test done?

In enzyme immunoassays (ELISA), antibodies, an enzyme and its substrate are used to detect proteins in food that may be allergens for some people; i.e. the proteins found in peanuts. There are variations in ELISA methods that 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 bound to the last antibody is added. This results in a change that 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 that measures the different masses of molecules within a sample, including proteins. These molecules are initially vaporized and are then struck by electrons. This gives each molecule or fragments of molecules a charge; if electrons are lost from the molecule then the molecule becomes positively charged while adding an electron to the molecule will result in a negative charge.

These ions are then sorted by charge and size based on how fast they are moving, as well as how much they deflect when a magnetic field is applied. Mass spectrometry can also be coupled with chromatography, such as liquid chromatography (LC-MS).

A 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 several peptides can be detected by mass spectrometry.

What are the advantages and disadvantages of each method?

ELISA has been reported to be sensitive and has the ability to detect allergens at levels of approximately 0.1 to 5 mg kg-1. However, it is difficult to know from what quantity the protein becomes an allergen, because of the differences in individual reactions. Another advantage of ELISA is that it is relatively easy to use and there are standards and validation tools readily available.

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 test could report a false positive result because the allergen is not present.

Differences in food preparation for testing may also affect the ELISA and therefore the final results. Other disadvantages include the fact that different antibodies and standards can be used for the same target protein, which can lead to different results.

As mentioned earlier, mass spectrometry can detect multiple target peptides at once, while maintaining the same level of sensitivity as ELISA. However, there may be some levels of assumption when quantifying peptides from data from