Seaweed as a sustainable source of food protein: maximizing seaweed protein content, protein recovery, and nutritional quality

Doctoral thesis, 2023

The rising global population and increasing demands for protein-rich diets pose a problem - we are running into limitations in our efforts to expand traditional protein sources, especially livestock-based. The issue arises from high carbon footprints connected to red meat production, finite amount of farmable land to produce more feed, and freshwater scarcity. For instance, 25 kg of feed is needed to produce 1 kg of beef, and around 68% of agricultural land is used for pasture. Increased use of marine protein sources can be part of a sustainable solution, not least seaweed which does not require feed, farmable land, and can grow in saltwater.

While some seaweeds have good amounts of protein, the contents are still lower than in legumes like soy. Also, seaweed contains many dietary fibers which makes it hard for our bodies to digest the proteins and take up its building blocks - the amino acids. Another problem is that certain brown seaweed species, like sugar kelp, can contain too much iodine. Despite being an important micronutrient, iodine can be harmful to us in high amounts. To reduce iodine amounts, the industry often soaks sugar kelp in warm water for a few minutes in a process called blanching.

This thesis explored the idea that we can increase the concentration of protein in seaweed using two strategies: adding nutrient-rich food process water residues to the seaweed cultivation media or producing seaweed protein ingredients. For the latter, we used both raw and blanched seaweed and tested two different extraction methods. Also, we examined the impact of these extraction methods on the digestibility of the seaweed and its protein ingredients using an "in vitro" test tube model.

By adding residual herring and shrimp process waters to tanks with seawater, we could more than double protein amounts in green seaweeds like sea lettuce, compared to cultivating them just with seawater. In the work with sugar kelp, we found that low blanching temperatures were equally good as high blanching temperatures at removing iodine. However, when using lower temperatures, we could extract more proteins from the seaweed. Furthermore, the protein ingredients we got from blanched sugar kelp - regardless of treatment temperature - could be consumed in 5 times higher amounts without reaching the tolerable upper intake of iodine, compared to protein extracts from unprocessed sugar kelp. An important learning was that seaweed protein extraction methods, such as the one we applied to sugar kelp, need to become more efficient and simplified to allow the commercialization of seaweed protein ingredients. Therefore, we invented an extraction method that combined solutions that can access proteins located in all parts of the seaweed. This new method was tested on sea lettuce and extracted more than 3 times the amount of protein compared to traditional methods. By simulating human digestion in vitro, we proved that an extracted seaweed protein ingredient was more digestible than the crude seaweed.

Altogether, this thesis opens possibilities for a more sustainable future, by transforming seaweed into a new food protein source. However, for this transition to happen, seaweed cultivation needs to be largely increased.