Chalmers University CirkAlg project advances seaweed protein with circular cultivation breakthrough

Seaweed has moved closer to becoming a viable large-scale protein source after researchers at Chalmers University of Technology completed a five-year project developing circular cultivation and extraction methods designed to improve yields, safety and digestibility.

• Chalmers University’s CirkAlg project has developed a two-step circular strategy to increase seaweed protein content and extract scalable protein ingredients.

• Cultivating sea lettuce in food industry process water has raised protein levels to those comparable to soybeans in follow-up studies.

• A new extraction method has increased protein yield more than threefold while reducing iodine and certain heavy metals.

The CirkAlg project, coordinated by Ingrid Undeland, Professor of Food Science at Chalmers, has focused on macroalgae, commonly known as seaweed, as part of efforts to diversify protein production with lower climate impact.

Macroalgae has attracted attention because it can be cultivated without farmland, fertilizer, irrigation or pesticides. It can also absorb nitrogen and phosphorus from surrounding waters and act as a carbon sink. However, despite its relatively high protein content and broad nutrient profile, several technical and safety challenges have limited its wider use in food systems.

“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,” said Undeland.

Yet brown seaweed species such as sugar kelp and finger kelp can accumulate high levels of iodine, which may exceed recommended daily intake even at low consumption levels. In some cases, seaweed can also bind heavy metals. In addition, seaweed proteins are tightly bound within the biomass, making them difficult to extract efficiently and, in some cases, challenging for the human digestive system to break down.

To address these constraints, CirkAlg developed a two-step production strategy involving partners from universities, food companies and the Swedish Food Agency.

The first step focused on increasing protein content during cultivation by growing seaweed in nutrient-rich process water streams generated by the food industry. Process water is produced during activities such as storage, peeling, heat treatment, marinating or transportation, and is typically expensive to purify and dispose of, despite often containing high levels of nitrogen and phosphorus. In seafood processing, it may also contain antioxidants and omega-3.

“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,” said Undeland.

In joint studies conducted by the University of Gothenburg’s Tjärnö Marine Laboratory and Chalmers, researchers cultivated seaweed with process water from herring, shrimp and oat industries. Water from the herring industry delivered particularly promising results in terms of growth and protein content. Sea lettuce showed strong performance, with follow-up studies reporting protein levels comparable to soybeans.

Sensory concerns were also evaluated. Although cultivation conditions can influence flavor, test panels reported that seaweed grown in herring process water did not display negative sensory effects, which had initially been a concern.

The second step of the strategy focused on extracting protein ingredients from cultivated seaweed using technologies designed to be scalable for industrial use. During his doctoral research within CirkAlg, João Trigo developed new methods for processing sugar kelp and sea lettuce.

For sugar kelp, which is known for high iodine levels, pre-treatment steps were optimized to lower iodine content prior to protein extraction. For sea lettuce, researchers developed a new extraction method capable of recovering a broader spectrum of proteins than traditional approaches.

“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,” said Trigo, who defended his thesis at Chalmers in October 2023.

The extraction process also concentrated vitamin B12 and omega-3 in the resulting ingredients. In vitro experiments indicated that proteins became more digestible after extraction. In addition, the technology reduced levels of certain heavy metals, including cadmium, particularly in brown kelp species.

Barbro Kollander, senior chemist at the Swedish Food Agency, led the work on iodine and heavy metals alongside Nathalie Scheers, Associate Professor at Chalmers. The project found significant differences between species and cultivation conditions.

“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,” said Kollander.

Scheers added, “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.”

Consumer surveys conducted within the project, led by Kristianstad University, showed a generally positive attitude toward seaweed as food. However, acceptance depended on appearance, taste and smell.

Undeland described the collaboration as a multidisciplinary effort spanning academia, regulatory authorities and industry. “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,” she said.

Results from the project are now being advanced through new collaborations involving Chalmers, the University of Gothenburg and Nordic Seafarm. The new protein extraction technology has also led to 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,” Undeland said.