A recent article published in Global Challenges proposed a novel approach to lowering mercury levels in fish meat during post-packaging storage, which could potentially extend its safe consumption period.
This method uses a cysteine-based aqueous solution to extract mercury from fish proteins, with the displaced mercury then captured on thiolated silica for removal.
Study: New Insight into Mercury Removal from Fish Meat Using a Single-Component Solution Containing cysteine. Image Credit: Dario Lo Presti/Shutterstock.com
Background
Fish is often considered a superfood due to its rich nutritional profile, but mercury contamination remains a significant concern. While various extraction solutions have been explored to reduce mercury levels in fish meat, limited data on different fish species and processing methods make it difficult to draw clear, systematic conclusions about their effectiveness.
Key factors such as pH, extraction time, solution volume, and the physical state of the fish also influence the overall efficiency of these methods, yet their precise roles are not fully understood. However, chelating agents like ethylenediaminetetraacetic acid (EDTA) and cysteine play a crucial role in mercury removal.
Developing extraction solutions based on these compounds for use during packaging and storage presents a promising strategy for reducing mercury levels in fish. This study introduces an improved extraction technique that utilizes a cysteine-based aqueous solution as a packaging medium to lower mercury content in fish meat.
Methods
This study examined the effects of extracting solution composition—specifically cysteine concentration—and the physical form of the fish on mercury removal efficiency.
First, cysteine solutions (0–5 wt%) were prepared by dissolving cysteine powder in ultrapure water. Fish samples, including whole fresh and canned tuna, minced canned tuna, and steamed tuna, were then submerged in the solution (80 wt%) for one hour at room temperature.
To evaluate how the liquid-to-fish ratio affects extraction performance, whole and minced canned tuna samples were placed in varying solution volumes (10–80 wt%). The time-dependent efficiency of mercury removal was also assessed over a period ranging from 1 to 12 hours.
The impact of mercury extraction on fish storage quality was monitored over 1–9 weeks, with assessments based on appearance, odor, and mercury content. In total, five types of fish samples were tested, including a fish protein standard, minced and whole albacore tuna canned in water, fresh tuna steak, and fresh tuna steak that had been steamed and pasteurized in the lab.
To facilitate mercury removal, thiol-functionalized silica particles were synthesized through a two-step process involving alkaline activation followed by thiolation of the calcined material. Adsorption tests were conducted using mercury extracts from the fish experiments as well as model solutions (0.3 mg/dm³) containing mercury stabilized in solution. Mercury adsorption efficiency was quantified using a direct mercury analyzer.
Results and Discussion
The efficiency of mercury extraction varied between 71% and 13% across different fish samples, following this order: fish protein extract > minced canned fish > steamed fresh fish > fresh fish > whole canned fish. This trend was largely due to the accessibility of fish tissue surfaces to the extracting solution.
Minced fish samples showed significantly higher extraction rates than whole pieces, as the solution had greater access to the tissue in shredded forms. In contrast, whole tuna pieces exhibited extraction rates three times lower due to restricted solution penetration.
Mercury removal was also influenced by cysteine concentration, with each fish type exhibiting a threshold beyond which further extraction was not possible. The most effective cysteine concentration was found to be 1.2 wt% for canned fish samples and 1.6 wt% for fish protein standards and fresh fish samples.
In canned tuna, mercury extraction reached approximately 13% after 50 minutes in a 1.2 wt% cysteine solution, then plateaued until the four-hour mark before increasing again due to the onset of fish spoilage.
Regarding mercury adsorption, the thiolated silica powder (thiolated via six hours of refluxing) demonstrated a methylmercury adsorption capacity of around 100 mg/g. This high capacity was considered sufficient for the experiments. Importantly, mercury was effectively bound to the thiol groups on the silica surface without interference from other compounds.
Conclusion
This study successfully demonstrated a simple and effective method for reducing mercury levels in tuna soaked in canning water-based solutions. Using a 1.2 wt% cysteine solution, researchers achieved a 35% reduction in mercury content in canned albacore tuna meat.
While higher cysteine concentrations generally improved mercury extraction, no definitive upper limit was identified. The effectiveness of extraction largely depended on factors such as the accessibility of mercury in fish muscle, tuna piece size, solution volume, and extraction time.
This safe and efficient approach offers a promising way to complement industry efforts in minimizing mercury exposure while enhancing the safety of fish consumption.
Journal Reference
Strachowski, P., Mandava, G., Lundqvist, J., Bordes, R., & Abdollahi, M. (2025). New Insight into Mercury Removal from Fish Meat Using a Single‐Component Solution Containing Cysteine. Global Challenges, 8(11). doi: 10.1002/gch2.202400161.https://onlinelibrary.wiley.com/doi/10.1002/gch2.202400161
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