Using DNA of peanuts to detect trace amounts of peanut in foods

Scientists have developed a sensitive test to detect trace amounts of peanuts in foods that uses the peanut’s DNA. This DNA-based method may benefit people with severe peanut allergies. For some people, eating even tiny amounts of peanuts can trigger anaphylaxis.

Anaphylaxis is a severe allergic reaction which has a rapid onset. Patients experience breathing difficulties, a sudden and intense feeling of fear and anxiety, and an accelerated heartbeat. They also experience confusion and lightheadedness due to a sharp and sudden drop in their blood pressure. Anaphylaxis can lead to unconsciousness and even death.

Caroline Puente-Lelievre and Anne C. Eischeid wrote about their study and new method in the Journal of Agricultural and Food Chemistry (citation below).

The two authors work at the Center for Food Safety and Applied Nutrition, which is part of the FDA. FDA stands for Food and Drug Administration. It is the US regulatory agency in charge of foods, cosmetics, tobacco products, medications, and medical devices.



Peanuts - detecting trace amounts
The new test is much more sensitive at detecting traces of peanuts in foods than other tests. (Image: http://alabamaliving.coop)

Millions of Americans allergic to peanuts

Surveys suggest that in the United States, at least three million people suffer from peanut allergies. Over the past ten years, the number of allergic Americans has been rising steadily.

People with a peanut allergy are usually extremely careful to avoid foods that contain the legume.

However, trace amounts of it may sometimes contaminate foods. They may even contaminate foods that do not list peanuts as one of their ingredients.

Detecting peanuts in foods

Over the years, scientists have developed many methods to detect peanut allergens in foods. However, the majority of them test for proteins that food processing destroys.

In contrast, DNA is typically much more stable than proteins. Other scientists have detected peanut nuclear DNA in foods using PCR (polymerase chain reaction).

However, there is only one nucleus in each cell. Plants, on the other hand, have many chloroplasts. Chloroplasts also have DNA in them.



The DNA of peanut chloroplasts have unique sequences that do not exist in other plants.

Puente-Lelievre and Eischeid wondered whether they could develop a test by targeting the DNA from the chloroplasts of peanuts.

Targeting three regions simultaneously

The scientists designed a PCR assay that could detect three short DNA sequences. Specifically, sequences that exist in the chloroplasts of peanuts.

If they could target the three regions simultaneously, the results would be more specific for peanut chloroplast DNA, the scientists wrote.

Spiking foods with peanuts

They then spiked six different foods with varying amounts of peanuts. The foods varied from tomato salsa to blueberry muffins.



The assay detected peanut traces in every food the scientists had spiked. Their new method had a detection limit of approximately 1 part per million (ppm). Previous PCR assays that targeted nuclear genes had a detection limit of 10 to 50 ppm.

In their research paper, the authors acknowledged funding from the FDA.

Citation

Development and Evaluation of a Real-Time PCR Multiplex Assay for the Detection of Allergenic Peanut Using Chloroplast DNA Markers,” Caroline Puente-Lelievre and Anne C. Eischeid. Agric. Food Chem, 2018, 66 (32), pp 8623–8629. DOI: 10.1021/acs.jafc.8b02053.