Melanotic blackening (melanosis) or blackspot is a common problem affecting the langoustine (nephrops) catch of UK fishermen, and can be more of a problem in warmer weather when water temperature rises.
For many years fishermen have used sodium metabisulphite to treat melanosis, but Seafish warns that this treatment has its drawbacks and there are alternative treatments readily available in the UK.
Melanosis is caused by the formation of coloured pigments in the shell and meat. It is a natural part of the spoilage process and while it does not pose a risk for human consumption, affected animals can be rejected by consumers due to their unsightly appearance.
“All fishermen want to land langoustines that are of the highest quality, taste good and meet all food legislation requirements, so careful treatment is essential,” said Mark Edmonds, Fisheries Technologist, Seafish.
“For many years using sodium metabisulphite has been the most popular choice for controlling melanosis. But there are known health and safety issues. Toxic sulphur dioxide gas can be released during the treatment process, it is highly corrosive and it can trigger asthma attacks and allergic reactions in vulnerable people. Legally there is a maximum residual limit on the amount of sulphite permitted in the finished product and all metabisulphite treated foods must be clearly labelled.
“These issues cannot be ignored so the way forward is clearly to source alternative, non-sulphite based treatments for langoustine. There are effective alternatives to sodium metabisulphite readily available in the UK which do not exhibit the same operational hazards as sodium metabisulphite, are competitive in preventing blackspot and give suppliers the ability to market an allergen free product,” said Mr Edmonds.
Whatever treatment is used it is crucial that fishermen and processors carry out the treatment process with great care and in accordance with the product manufacturers’ instructions. To help guide fishermen and processors through the operational process of such treatments, Seafish and Seafood Scotland have produced a number of information documents with details of alternative treatments and step-by-step instructions on their usage.
These documents highlight the need for vessels to standardise their methods of application to consistently produce a quality product. The guidelines cover correct crew training, applying the right dosage and ensuring good hygiene practices. A laminated user card is also available, which is completed by the crew and displays the measures and dip times used onboard. This serves as a useful visual reminder in ensuring that the correct procedures are followed.
