The microalga Nannochloropsis oceanica holds potential as a valuable source of sustainably produced nutrients such as protein, omega-3 fatty acids, and vitamin K2. A new study from DTU shows that cultivation conditions, particularly temperature and light, play a significant role in the yield.

The world is searching for sustainable solutions for future food production, and microalgae appear to have the potential to play a crucial role. The microalga Nannochloropsis oceanica is particularly interesting because it can produce large amounts of protein, the essential omega-3 fatty acid EPA, and vitamin K2. But which conditions are needed to ensure efficient production? A new study from DTU National Food Institute shows that temperature and light are key factors in the yield of various nutrients.

"Much of the existing research focuses on how Nannochloropsis oceanica grows and produces biomass, as well as on fatty acid production. At the DTU National Food Institute, we have also examined this; however, we have additionally chosen to compare it with the simultaneous production of proteins and vitamin K2," says PhD student Emil Gundersen, who conducted the cultivation experiments in the microalgae laboratory at the DTU National Food Institute.

The research provides a more comprehensive overview by simultaneously analysing the protein content, fatty acid content, vitamin K content, and the microalgae's growth. With this knowledge, the cultivation phase can be optimised to achieve the most nutrient-rich biomass.

"Our experiments show that if temperature and light intensity are high, Nannochloropsis oceanica grows quickly and produces a lot of protein. However, the content of omega-3 and vitamin K2 is higher when the temperature is lowered," says Emil Gundersen.

Two-stage cultivation

Based on the research, the scientists propose cultivating Nannochloropsis oceanica using a two-stage process.

"The research suggests that we will achieve the best results if the microalgae are initially cultivated at high temperatures and under strong light to promote growth and protein production. Subsequently, conditions can be adjusted by lowering the temperature, allowing the microalgae to focus on producing omega-3 and vitamin K2," says Emil Gundersen.

The results of the study are based on the cultivation of relatively small amounts of microalgae in the laboratory, but the researchers expect that the overall trends will also apply on a larger scale.

"Temperature regulation is a well-known concept in the current fermentation industry. Therefore, we believe it will be relatively easy to implement a two-stage process based on temperature in future commercial production of microalgae," says Emil Gundersen.

The potential of algal vitamin production

Vitamin K2 is typically obtained through animal-based foods such as meat and dairy products, making it harder to acquire when switching to a predominantly plant-based diet.

"It is interesting that microalgae could potentially serve as a source for producing vitamins like K2, which we usually obtain from animal sources, in a vegan way," says Emil Gundersen.

The next step is to investigate how the bioavailability of the proteins, omega-3 fatty acids, and vitamins in the microalga can be increased. This is necessary as they have a thick cell wall that is difficult for the human digestive system to break down.

Why cultivate microalgae?

Microalgae are organisms that can grow using light and CO2, much like plants. They can be cultivated in photobioreactors, which consist of a system of plexiglass tubes where the microalgae receive light and air.

Compared to the bacterial production of biomass through fermentation, for which Denmark is well known, the microalgae industry is still relatively small. This is likely because microalgae cultivation in Denmark, due to the climate, requires high-tech indoor systems. In Southern Europe, the warmer climate allows for cultivation in outdoor tanks, saving both materials and energy.

Nonetheless, microalgae remain attractive in cooler climates, primarily due to their unique nutritional composition, which includes essential amino acids, unsaturated long-chain fatty acids, and a wide range of vitamins and minerals. Additionally, they can be cultivated on land that is otherwise unsuitable for agricultural production and can be powered mainly by renewable energy.

"Since microalgae are cultivated using light and CO2, they save on the input of organic carbon, typically sugar, which is required in traditional fermentation. Moreover, they need some inorganic nutrients, which can potentially be supplied by utilising wastewater from other industries," says Emil Gundersen.

Facts about the scientific article

Title: Nannochloropsis oceanica as a Source of Bioactive Compounds: Mapping the Effects of Cultivation Conditions on Biomass Productivity and Composition Using Response Surface Methodology

The article is part of the research project MASSPROVIT, funded by the Independent Research Fund Denmark.

Authors: Emil Gundersen, Jette Jakobsen, Susan Løvstad Holdt, and Charlotte Jacobsen, all from DTU National Food Institute.