"Stabilization of Ulva sp. biomass and its effects on nutritional properties, microstructure, technofunctionality and the development of volatile compounds"

Swedish cultivation of macroalgae, also known as seaweed, has in a short time gone from nothing to a rapidly growing industry with great plans for the future. Mar Vall-Llosera, a Blue Food PhD student at Chalmers University of Technology, is studying algae in her PhD project and the results of her work can help the Swedish algae industry to really take off and, not least, increase the use of green algae as a new food ingredient.

Mar Vall-Llosera for algae cultivation
Mar Vall-Llosera, Chalmers

Algae have the advantage of not needing to be watered or fertilized, unlike plants grown on land. On the contrary, they can provide a clean environmental service by taking nutrients from our oceans, or from nutrient-rich process water streams, and returning them to the food chain. The latter is currently being explored in the larger project that Mar is also part of, BlueGreen.

The high water content of algae, which is adapted to cold temperatures, poses a risk of microbial growth and rapid degradation of nutrients after harvesting. Freshly harvested algae therefore need to be stabilized, for example by freezing, drying, fermenting or salting. The first part of Mar Vall-Llosera's project is to investigate which method works best to extend shelf life and preserve substances such as proteins, polyphenols, fatty acids and vitamins.

Evaluate methods to increase stability

Mar Vall-Llosera is studying the green algae sea lettuce, Ulva fenestrata, which is less sensitive to changes in salinity, temperature and nutrient content of the water compared to other algae species, and which has not been studied as much as brown algae. Her first step is to find out how to stabilize the algae using salt and sugar. The saline solutions she uses contain between 5 and 25 % salt, much more than seawater, which has a salt content of around 3.5 %. She specifically monitors pH, aroma, texture and color, and examines which microorganisms increase in number, whether they are harmful, whether there is a particularly prominent microorganism and how it can be prevented.

In addition to finding out how salting, freezing, drying and fermentation affect shelf life, Mar Vall-Llosera wants to find out what other effects the different methods have, such as how they affect the physical properties of the seaweed, its chemical composition and the degradability of nutrients in the stomach and intestines. For example, whether proteins are released into the brine or whether freezing causes the cell walls to break down and affects the structure of the algae, causing it to lose its elasticity.

Much research has been done on brown algae and there are also some previous studies on drying and freezing green algae. However, there are no experiments comparing different stabilization methods and their different effects on green algae. After the first year, Mar Vall-Llosera hopes to have a more solid knowledge base.

Brown algae grow very well and provide more material, but green algae have other advantages, including a higher protein content and, unlike brown algae, green algae do not have the high iodine content that limits their use. Interest in green algae is growing, as is its use.

Algae as such or as an ingredient in composite products

Once the knowledge of different methods to extend the shelf life of algae is in place, the next step is to find out how they can be used. This could be a so-called 'gelled' product such as a burger, or an emulsion such as a drink, smoothie or sauce. Or even as an ingredient that increases the saltiness, umami taste or the amount of antioxidants in a food.

Algae can either be used as they are - dried, pickled, in a salad - or as an ingredient in a composite product, such as breakfast cereals or bread, where they can add an extra layer of flavor.

Algae can be used to add saltiness or flavor to food, for example, replacing salt with an algae ingredient can reduce the amount of sodium chloride, or common table salt, in Vienna sausages by up to 10% without affecting the taste.

The project uses algae grown in tanks at the Tjärnö marine laboratory, which makes it possible to obtain smaller quantities throughout the year, even during the non-algae season. In the future, Mar Vall-Llosera also plans to test the most promising methods on larger quantities of algae grown at sea. She will also participate in trials to grow algae in process water from the fish industry, a by-product of salting and marinating herring, to see if the content of protein or other substances in the algae can be increased. The biomass used in the project is grown at the Tjärnö marine laboratory by Sophie Steinhagen, as part of the BlueGreen project.

Studies at close quarters

When the algae are treated in different ways, they also change at the cellular level. In parallel to evaluating how the different treatment methods affect, for example, the durability of the algae, Mar Vall-Llosera will also study what happens at the small scale using microscopy. By studying in detail what happens to the cell walls when the different methods are used, she hopes to figure out how properties related to texture and degradability in the stomach and intestines are affected.

Much of the work is based on experiments and trials in the laboratory and Mar Vall-Llosera thinks she has a very good balance between planning, work in the lab and analysis work. Working in the lab gives you the opportunity to see changes and draw conclusions.

Sweden is a good place to grow algae

There are several advantages to growing algae in Sweden. Not only are Swedish waters relatively clean, but algae farming helps to combat eutrophication and increase biodiversity. Mar Vall-Llosera hopes that her work will increase interest in the cultivation of green algae and show new opportunities to use a versatile raw material.

Mar Vall-Llosera's Chalmer colleague John Axelsson is also a Blue Food PhD student. She hopes that in the future they will be able to collaborate and combine their ingredients - hers from algae, his from herring - in a joint product. If so, it will be a concrete result of a project that paves the way for greater Swedish cultivation and use of algae.

The project is particularly relevant to Blå Mat's research area 2: Process technologies and product development.

The Mar Vall-Llosera project is expected to be completed in 2025.

Supervisors

Ingrid Undeland

Assistant supervisor

Henrik Pavia, GU
Anna Ström, Chalmers

Mar Vall-Llosera's profile page on chalmers.se (in English)