Tuna Sandwich Mystery: Was There Really No Tuna DNA in America's Largest Sandwich Chain?

Tuna is high in protein and the most popular shelf-stable seafood in the United States. The popular Subway sandwich chain uses this fish for their foot-long tuna sandwich that their customers love.

However, earlier this year, the restaurant received criticisms after two of its customers claim that they are serving sandwiches that may not contain any tuna after a laboratory test did not found any tuna DNA at all.

But molecular ecologist Karen James of the University of Maine told Inverse that must be more worried about sustainable fishing practices and mislabelling of products rather than not finding tuna DNA in the sandwich.

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Tuna Sandwich Mystery: Was There Really No Tuna DNA in America's Largest Sandwich Chain?

Lawsuit Against Subway

The Washington Post reported in late January that the world's largest sandwich chain is currently facing a class-action lawsuit in the state of California, claiming that the food chain is serving fake tuna sandwiches.

The lawsuit was filed by the Lanier Law Firm of Houston, Texas, and Shalini Dogra of Dogra Law Group of Santa Monica, California, on behalf of two Alameda County, California residents named Karen Dhanowa and Nilima Amin.

Forbes reported that the two claimed they "were tricked into buying food items that wholly lacked the ingredients they reasonably thought they were purchasing."

In a statement, Subway refused the allegations, saying, "There simply is no truth to the allegations in the complaint that was filed in California. Subway delivers 100% cooked tuna to its restaurants, which is mixed with mayonnaise and used in freshly made sandwiches, wraps, and salads that are served to and enjoyed by our guests."

But then, last month, The New York Times released a news article that the test results from a commercial food testing lab revealed that there is no detectable tuna DNA in their sandwich.

On the other hand, the plaintiffs have walked back their claim in January, saying instead that the tuna served in the restaurant's sandwich is not sustainably caught as the restaurant claims. However, the issue has already caught the attention of the media.

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Is There Tuna in the Subway Sandwich?

After the article in the Times was published, it created a buzz, and James said that there could be other reasons why the tuna DNA was not detected, not just because the meat used was a mystery.

James explains to Inverse that the DNA in the environment could get damaged when the organism dies. Environmental factors, like getting broken or fragmented, could be the reason. The cells could slowly degrade and compromises the DNA inside.

She added that any DNA damage could make it more difficult for scientists to successfully detect DNA from the sample. To test the DNA in food, James said that the lab would have done a polymerase chain reaction (PCR) test to isolate the DNA, create copies of it, and compare the results against an authentic DNA sample of the tuna. This is essentially similar to testing SARS-CoV-2 in swab samples.

This process could be a little challenging. Assuming that the DNA was not too damaged, the lab would have needed a number of control samples as well as samples that are covered in mayonnaise.

Nonetheless, James said that she is willing to bet that if she would eat a tuna sandwich in Subway, there will be a real tuna fish in the sandwich and not a mysterious concoction.