Fish is an excellent source of high-quality protein, rich in omega-3 fatty acids and various other essential nutrients. Yet, there are concerns about the accumulation of harmful mercury, especially in types like tuna. Recent research has introduced an innovative method for packaging canned tuna, involving a water-based solution containing the amino acid cysteine. This technique has been shown to reduce the mercury content in canned tuna by as much as 35%, thereby lowering the risk of mercury exposure through dietary intake.
Fish and seafood offer a diverse array of vital nutrients, but consuming certain fish can also pose risks due to the presence of methylmercury, a particularly toxic form of mercury. Methylmercury tends to accumulate in fish, particularly in species near the top of the food chain like tuna, as it binds with proteins in their tissues.
New packaging method helps reduce mercury
The World Health Organization (WHO) categorizes mercury as one of the ten most dangerous chemicals for humans. Exposure can harm the central nervous system, with unborn and young children being especially vulnerable. Consequently, dietary guidelines advise pregnant women to be cautious about eating tuna.
“Our research indicates alternative ways of addressing mercury contamination in tuna beyond merely reducing its consumption. We aim to enhance food safety and promote better human health, along with enabling better use of food that currently faces restrictions,” explains Mehdi Abdollahi, Associate Professor at Chalmers University of Technology, who leads a project named Detoxpak.
The idea behind active packaging involves creating materials, such as a liquid inside a can, that engage with the food during its storage to potentially extend its shelf life. However, this approach has never been utilized before to enhance food safety.
In an earlier study, researchers explored coating packages with thiolated silica to capture mercury from canned fish but found that the bonds holding mercury in tuna tissue made it difficult to extract.
Tuna tissue proteins, particularly those rich in sulfur-containing amino acids, attract and retain mercury due to strong interactions from thiol groups present in these amino acids. “Understanding this, we added cysteine to a water solution that could immerse the fish. We believed this method would promote the removal of some mercury, allowing it to bind to the solution instead. Further studies are necessary to manage the mercury that is removed,” says Przemyslaw Strachowski, the lead author and at the time a postdoctoral researcher in the Department of Life Sciences at Chalmers.
Removable mercury levels reach 35 percent
The study revealed that a larger surface area of fish exposed to the cysteine solution resulted in greater mercury uptake. The maximum mercury reduction observed was 35 percent when canned minced tuna from grocery stores was tested. Researchers also found that a maximum contact period of two weeks was effective, after which no further change was observed.
However, in this investigation, no significant differences in the appearance or odor of the fish samples were noted. Cell-based tests have verified the safety of this new technology.
“The beauty of this kind of packaging is its active state while the product is stored on shelves. If this method were to be implemented in the industry, no extra production steps would be required. Our findings could enhance the safety margin for fish consumers,” adds Przemyslaw Strachowski.
Method details:
- The study utilized various fish protein extracts, including dry powder, fresh and lab-steamed fish, both in fillet and minced forms, as well as commercially available canned tuna in larger pieces and minced.
- No additional additives, such as pH adjusters, were used in this process; only the concentration of cysteine in the water was modified. Increasing cysteine levels improved the removal of mercury, up to an optimal concentration of 1.2 percent.
This study received funding from Formas.
