Smart Packaging New Packaging Solution Can Reduce Mercury Content in Tuna

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Chalmers University of Technology

KNF Neuberger GmbH

Researchers have explored a new method under which tuna is packaged in a water-based solution containing the amino acid cysteine. With the help of this new packaging solution, up to 35 percent of the mercury content can be removed from the tuna.

Gothenburg/Sweden – Fish is rich in protein, omega-3 fatty acids and other important nutrients. At the same time, toxic mercury accumulates in fish, especially in predatory fish such as tuna, which also means that humans can ingest it. Researchers at Chalmers University of Technology have investigated a new method in which tuna is packaged in a water-based solution containing the amino acid cysteine, which can bind mercury. The results showed that up to 35 percent of the mercury in the tuna could be removed using the solution.

When we eat fish and shellfish, we get a variety of important nutrients, but we also risk exposure to the most toxic form of mercury, methylmercury. The substance accumulates in fish, especially fish species high up the food chain, such as tuna, because mercury binds to proteins in the tissues.

Packaging solution draws out mercury

According to the World Health Organization, WHO, mercury is one of the ten most harmful chemicals to humans. Exposure can damage the central nervous system, and fetuses and young children are particularly sensitive. Therefore, there are recommendations regarding tuna consumption for pregnant women.

– Our study shows that there are other ways to address mercury contamination in fish than limiting consumption. Our goal is to increase food safety and contribute to better health, but also to make a food that is currently under certain restrictions more accessible, says Mehdi Abdollahi, associate professor at the Department of Life Sciences at Chalmers and coordinator of the Detoxpax project.

The idea behind so-called active packaging is to develop materials, such as a liquid inside a can, that interact with the food during storage to, for example, increase shelf life. But the concept has never before been used to improve food safety.

In a previous study, the researchers investigated the possibility of coating the inside of packaging with a layer of thiolated silica to capture mercury from the packaged fish. Thiols are organic compounds that contain a specific sulfur group that binds tightly to mercury. During their experiments, they observed that the forces that bind the mercury in the fish tissue prevented it from escaping from the fish flesh.

Proteins in tuna tissues, especially sulfur-containing amino acids, bind tightly to − and accumulate − mercury due to the strong interactions with the thiol groups in the amino acids.

“Knowing this, we decided to add an amino acid, cysteine, to an aqueous solution in which the fish meat can be stored. Our hypothesis was that this would cause some of the mercury to be released from the meat and instead be bound in the solution and discarded. Further research into how the removed mercury should be handled is required going forward,” says Przemysław Strachowski, the study's first author and postdoctoral researcher at the Department of Life Sciences at Chalmers at the time of the study.

Up to 35 percent of the mercury was removed

In the study, the researchers discovered that the larger the surface area of the fish meat that was in contact with the cysteine solution, the higher the mercury absorption. The highest value for mercury reduction, 35 percent, was achieved when testing ground tuna meat from canned food available in regular grocery stores. They also observed that the maximum limit for absorption was reached after two weeks.

In the current study, the researchers did not notice any noticeable changes in the appearance or odor of the fish samples tested. Cell-based tests have also confirmed the safety of the developed technology.

“The beauty of this type of packaging is that it is active while the product is on the shelf. No additional production steps would be needed if a method like this were used industrially, and the application of our results could increase the safety margin for fish consumption,” says Przemysław Strachowski.

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