Shrimp farmers, fishermen and processors in Australia, Mexico, Ecuador, Colombia and Brazil are reporting encouraging results following recent trials using a new and safe treatment to prevent ‘blackspot’ or melanosis in the harvested product.
Crustacean farmers, processors and fishermen have traditionally used sodium metabisulphite as a treatment to prevent ‘blackspot’ in a variety of species of warm and coldwater prawns, which is a natural process that discolours the shell after harvesting. Although blackspot is harmless, it does affect the appearance of the prawns, which in turn can make marketing difficult and increases the reject rate.
However, sodium metabisulphite is a far from satisfactory treatment, given the well-documented evidence that sulphite based treatments are hazardous to the health of farm and processing workers because the sulphur dioxide fumes released during treatment can harm operator’s airways and lungs. Metabisulphite is also corrosive and can cause serious damage to equipment in processing factories.
However, there are alternative and more effective treatments. One of these is Prawnfresh, which is produced by UK company Xyrex. Shellfish farmers, processors and fishermen who are already using this liquid solution treatment have found immediate benefits. The active ingredient in Prawnfresh is safe to use and leaves no chemical residues or taints. It works by inhibiting the enzyme present in the prawn that results in melanotic blackening. The application of the treatment is very straightforward and involves dipping the harvested prawns into a tank containing saltwater with Prawnfresh added at a ratio of 1:1000.
Seafarm in Queensland, Australia, is one company that has benefited from using Prawnfresh, which it uses to treat its farmed banana prawns (Fenneropenaeus merguiensis) at its Crystal Bay Prawns brand operation.
Dr Trevor Anderson, general manager of Seafarm, says: “Prawnfresh allows the sweet natural flavour of Crystal Bay Prawns to come through. The environmental approach of Xyrex and the natural ingredients in Prawnfresh is a natural fit with our chemical free natural Crystal Bay prawns grown in the pristine waters of Australia.
“It also ensures that we avoid sulphur allergy issues in our customers and processing staff. It means we can offer our customers a product, which is safer, healthier and more natural. It also overcomes the problem we find with metabisulphite, which results in erosion of the shell.”
John Davis, the managing director of Xyrex, says: “Trials are also ongoing in shrimp and prawn farming operations in Ecuador, Mexico, Columbia and Brazil, and the feedback has been very positive. On the back of these results, we are hopeful that the use of Prawnfresh will be expanded into processors and shipping fleets in these areas.”
In northern Europe, fishermen and processors of the langoustine species, Nephrops norvegicus, have successfully used Prawnfresh for a number of years. Donald Kristensen, managing director of Danish seafood processor Royal Fish Denmark A/S, says he has noticed a big improvement in the welfare of his processing employees after switching from sodium metabisulphite to Prawnfresh.
“All our employees used to have general breathing problems including irritated eyes and nose. This is no longer an issue after changing to Prawnfresh. Tests have shown that prawns treated with Prawnfresh stays nicer in colour, texture and odour, longer than raw material treated with sodium metabisulphite. We also feel it is a healthier additive for the consumer.”
Independent testing by the UK Sea Fish Industry Authority supports these findings. Trials by Seafish in 2005 found that prawns treated with 5% metabisulphite lose some visual qualities through bleaching and attain high sulphite residues, often above the permitted 150ppm. Furthermore, prawns treated with high concentration sodium metabisulphite were found to have poor flavour. Of the various alternative treatments tested, Prawnfresh was found to deliver the best results.