Research has paved the way for seaweed as a future protein source

Macroalgae, commonly called seaweed, has a relatively high protein content and can be cultivated with minimal climate impact. In the long run, it could therefore become a competitive alternative or complement to climate-heavy such as red meat. Growing seaweed requires no farmland, fertilizer, irrigation, or pesticides. Instead, seaweed provides an environmental service by remediating nitrogen and phosphorus from our waters and by acting as a carbon sink.

"From a food perspective, seaweed contains, in addition to protein, dietary fibers and a very broad palette of interesting micronutrients such as vitamin B12, minerals, and small amounts of marine omega-3. Also, seaweed has a very interesting taste profile rich in for example umami and saltiness”, says Ingrid Undeland, Professor of Food Science at Chalmers who has coordinated the project.

There are, however, certain challenges. The proteins can be difficult for our digestive system to break down, and brown seaweed species like sugar kelp and finger kelp can accumulate very high levels of iodine, which even after low consumption can exceed the recommended daily iodine intake. In some cases, seaweed can also bind heavy metals.

Strategy in two steps

For seaweed to become an attractive, tasty and safe protein source, the CirkAlg project, a collaboration between universities, food companies, and a government agency (see fact box below), developed a two-step production strategy. 

In the first step, they aimed to increase the protein content of the seaweed by growing it together with nutrient-rich process water streams from various food industries. The second step focused on developing technologies, which should be industrially scalable, to extract proteins from the cultivated seaweed. In both steps, sensory parameters, as well as nutritional and safety aspects, were considered.

Seaweed cultivated in process water

Process water is generated in almost all food industries, for example during storage, peeling, heat treatment, marinating, or transportation of food. It is currently expensive for companies to purify and dispose of this water, paradoxically since it can be very rich in nutrients such as nitrogen and phosphorus in different forms.

"Some examples are marinades from pickled herring production as well as cooking and peeling water from the shrimp industry. The nutrients in these waters may however be recovered and returned to the food production chain – this circular thinking was one of the core ideas behind the CirkAlg project," says Ingrid Undeland.

In several joint studies by the University of Gothenburg (Tjärnö Marine laboratory) and Chalmers, seaweed was cultivated in presence of process water from herring, shrimp, and oat industries. It was observed that, among other things, water from the herring industry gave promising results for both the growth and protein content of the seaweed. Especially sea lettuce showed good results, with protein content in subsequent follow-up studies increasing to levels comparable to soybeans. 

Consumer surveys

Consumers have a positive attitude towards seaweed as food. This was shown in the consumer-focused surveys conducted within CirkAlg, led by Kristianstad University.

Whether they choose to put it on their plates however depends on how the food is perceived in terms of appearance, taste, and smell. Although cultivation conditions can affect the sensory profile of seaweed, the seaweed generated in CirkAlg was not affected by the cultivation with herring process water according to test panels, which was an initial concern for the researchers.

New protein ingredients

During João Trigo’s PhD research at Chalmers, the team also developed protein ingredients from sugar kelp and sea lettuce. For sugar kelp, which contains very high levels of iodine, pre-treatments were optimized to lower iodine levels before extracting the proteins.

For sea lettuce, a completely new extraction method was developed that could recover a broader spectrum of proteins than traditional methods so far have been able to do. While the protein yield increased with the new method, it also concentrated both vitamin B12 and omega-3. Further in vitro experiments showed that seaweed proteins became more digestible after extraction.

"With the new technology, protein yield increased by more than threefold compared to our reference method. This marks a significant advancement as seaweed proteins are more diverse and tightly bound in seaweed than those in sources like beans and peas, making extraction much more challenging. Low yields have long been a bottleneck in the development of seaweed protein ingredients, but we believe we are changing that paradigm," says João Trigo, who defended his thesis within the CirkAlg project at Chalmers in October 2023. 

Seaweed is not one homogenous food raw material

The extraction technology could also lower the levels of some heavy metals such as cadmium, results that have a greater bearing on the brown kelp species than on green species such as sea lettuce. The latter had significantly lower levels of heavy metals, as shown by the large number of analyses performed within the project.

"The differences we saw in CirkAlg clearly illustrate that you should consider both different seaweed species and their cultivation conditions individually when it comes to processing needs and future seaweed consumption, in the same way as is done today for different types of vegetables and grains," says Barbro Kollander, senior chemist at the Swedish Food Agency, who led the work package on iodine and heavy metals together with Nathalie Scheers, Associate Professor at the Division of Food and Nutrition Science at Chalmers.

Nathalie Scheers further explains:

“It is also important to consider how different foods affect our absorption of heavy metals differently. In pilot studies using intestinal cells, we observed that cadmium absorption from sugar kelp was limited, though this needs to be verified in further studies”, 

”Fruitful multidisciplinary collaboration”

The past five years have shown completely new possibilities for using seaweed cultivation to circulate lost nutrients back into the food chain – while making seaweed a promising protein source.

“The collaboration within CirkAlg has been incredibly rewarding, with a multidisciplinary breadth, and great commitment from both the Swedish Food Agency and several food companies," says Ingrid Undeland.

The results from CirkAlg are now being carried forward within the framework of new collaborative projects between, among others, Chalmers, the University of Gothenburg and Nordic Seafarm, and regarding the new protein extraction technology, it has generated a patent application.

“Although more work is still needed to optimize and scale up this circular solution that can provide new alternative proteins on our plates, CirkAlg has taken very important initial steps towards a completely new blue development," says Ingrid Undeland.

More about CirkAlg

• Read more about the project on Chalmers' website: CirkAlg
• Read the latest press release from Chalmers about the project's reseach: The blue-green sustainable proteins of seaweed may soon be on your plate
• Read a press release from the University of Gothenburg: Residual water from the food industry gives seaweed cultivation a boost 

Read the two pHd-thesis from the project

• João Trigo: “Seaweed as a source of food protein ingredients: Maximizing seaweed protein levels, protein recovery, and nutritional quality”.Chalmers University of Technology. 
• Kristoffer Stedt “Seaweeds as a future protein source: innovative cultivation methods for protein production”,University of Gothenburg, 2023.

Collaborating Organisations

• University of Gothenburg (Academic, Sweden)
• Kristianstad University (Academic, Sweden)
• National food agency, Sweden (Public, Sweden)
• Oatly AB (Private, Sweden)
• Gastroba Utvecklings AB/VegMe (Private, Sweden)
• Sweden Shellfish AB (Private, Sweden)
• Nordic SeaFarm AB (Private, Sweden)
• Sweden Pelagic AB (Private, Sweden)