Doctoral student looks at seaweed.
Kristoffer Stedt harvesting sea lettuce at a farm in the sea outside Tjärnö Marine Laboratory.
Photo: Sophie Steinhagen

Seaweeds have the potential to replace soya beans as protein source


Seaweeds grown in Sweden have the potential to become an important ingredient in the foods of the future. A new thesis from the University of Gothenburg shows that the protein content of the seaweed sea lettuce can be increased to the same level as soybeans.

With a growing population and increasing pressure on land-based agriculture, focus is turning to food from the sea. In a recent thesis, Kristoffer Stedt, a PhD student at the Department of Marine Sciences, investigates seaweeds as a future source of protein.

"Seaweeds contain many important nutrients such as proteins, minerals, and vitamins and have potential to be an important part of our diet. Within five years, I think we will see many new seaweed products on the market," he says.

Protein content more than doubled

In his thesis 'Seaweeds as a future protein source', Kristoffer Stedt examined the protein content of four seaweed species. Early on, the green seaweed sea lettuce proved to be a candidate worth looking at more closely. The seaweed, which resembles thin leaves of iceberg lettuce, is fast-growing and varies in protein content depending on where it grows. This makes it possible to increase the protein content through the nutrient composition of the water in which it is grown.

"I collected sea lettuce from sea farms and let them grow in residual water from the food industry. After two weeks in the nutrient-rich water, the protein content had more than doubled," says Kristoffer Stedt.

Alger i odlingsrör.
When algae are grown in wastewater, they grow faster and have a higher protein content. In this way, residual water can be transformed from a cost to a resource for the food industry.
Photo: Karin Björk

Sea lettuce grown on the west coast of Sweden has a protein content of around 15 per cent in dry weight. By cultivating the seaweed in process water, Kristoffer Stedt has shown that it is possible to increase the protein content to 37 per cent. This is on a par with soybeans, which have a protein content around 40 per cent. 

"If we can replace soybeans with Swedish-grown seaweeds, we would make several environmental benefits. We would get a locally produced protein source that doesn't compete with land-based cultivation and contributes to reducing the eutrophication of the ocean.”

Seaweeds adds value to other foods

Kristoffer Stedt,
Kristoffer Stedt, PhD student at the Department of Marine Sciences at the University of Gothenburg.

One challenge however, is that the proteins in seaweeds are more tightly bound than in soybeans. Therefore, the proteins are easier for the body to absorb if they are extracted from the seaweed, which is something that Kristoffer Stedt's colleagues at Chalmers University of Technology are investigating in the CirkAlg project.

"Sea lettuce contains both fat-soluble and water-soluble proteins. This means that several steps are required to extract them. The researchers at Chalmers are now working to develop such a two-step process and have shown very positive results."

Which seaweed products do you believe in the most?

"I think seaweeds can play a role in many different ways, including the use of the proteins as a complement to minced meat and soy products. In the future, I think we will see products like seaweed burgers in the super market. In addition, the omega-3 and vitamin B12 content of seaweeds adds value to the products, which means that the algae also could be used as additives in other vegetarian foods."

Link to thesisSeaweeds as a future protein source: innovative cultivation methods for protein production

Contact: Kristoffer Stedt, PhD student at the Department of Marine Sciences at the University of Gothenburg, phone: 0766-22 96 77, e-post: 

Text: Karl-Johan Nylén

Facts about sea lettuce

Sea lettuce is one of several species in the green algae genus Ulva. In Sweden, sea lettuce grows on rocks and stones at the water's edge along the entire west coast and in the south of the Baltic Sea. In recent years, the species has started to be cultivated on the Swedish west coast. Sea lettuce has good nutritional values with a relatively high protein content, beneficial polyunsaturated fats and dietary fibre. It also contains various valuable biochemical molecules.