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Is Danish Seaweed Safe to Eat?

30 December 2014

DENMARK - Scientists have reviewed literature to discover if there are undesirable bacteria and other microorganisms on edible seaweed from the Danish coastal areas. There is good news, since it would appear that there are no pathogenic microorganisms to pose a risk to seaweed-eaters.

In Denmark many species of seaweed are harvested and eaten. Therefore, the Danish Veterinary and Food Administration asked DCA – Danish Centre for Food and Agriculture to investigate the importance of pathogenic microorganisms in marine environments for the harvesting or cultivation of seaweed as a food product. The results have been published in a report by DCA.

In Denmark 10 particular species or genera of edible seaweed are collected and eaten. These belong to both the green, brown and red groups of algae. When the seaweeds are gently swaying in the waves, they share the water with a sea of other organisms. This means that the seaweed we eat is not grown in a sterile environment. The question is whether this has any implications for our health when we eat seaweed.

Many microorganisms are normally present on seaweed. They can form a biofilm on the surface of the weed. These are primarily bacteria from the surrounding water. The composition of the bacterial flora is determined by a number of factors and there is strong competition between the bacteria in the biofilm.

"The bacteria that establish in the biofilm are specially adapted," explain the two authors of the report, Senior Researcher Niels Bohse Hendriksen from the Department of Environmental Science and Academic Employee Steffen Lundsteen from the Department of Bioscience.

"We believe that microorganisms that are pathogenic to humans are not specifically adapted to life on the surface of seaweed plants and are therefore unlikely to survive, grow and establish on seaweed, they say."

However, this does not mean that pathogenic bacteria cannot occur on seaweed for shorter periods. This will happen on seaweed in locations with poor bathing water quality or in connection with heavy rainfall where sewage is discharged untreated into the water. This is especially a problem in coastal areas with shallow, stagnant water.

There are approximately 350 seaweed species in Danish waters, but only a few of the species are used for eating. Seaweed requires light, salt water and a stone or other solid substance to attach to in order to grow and thrive. In the report, the scientists describe various aspects relating to seaweed in general and to the specific species used for eating. They also explain the presence of microorganisms on the seaweed and the biological, physical and chemical conditions that can affect the growth of these microorganisms. The report provides an overview of the specific bacteria that can be found on seaweed in Danish waters.

The report (in Danish) ”Forekomst af mikroorganismer på tang – specielt på spiseligt tang, der forekommer i de danske farvande” (“The presence of microorganisms on seaweed - particularly in the edible seaweed found in Danish waters”, DCA report no. 48, November 2014, can be downloaded here.

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