Microalgae represent a valuable renewable resource, but they are still little-known. These photosynthetic microorganisms, such as spirulina or chlorella are mainly used for human and animal nutrition. However, their potential extends far beyond this, with applications in healthcare, cosmetics, fine chemistry and biomaterials production. Their high production costs are holding back their development. In addition, their quality, particularly their composition and purity varies according to the production method used. This must be chosen according to the molecules of interest sought for the valorization of microalgae.
Exceptional carbon-fixing capacities
Like plants microalgae produced by photosynthesis fix CO2. They can also exploit various sources of organic carbon, enabling them to produce molecules of interest such as polyunsaturated fatty acids, carotenoids (antioxidants) and phytosterols (anti-aging agents).
Chlorella are rich in proteins, vitamins and minerals, and stand out for their ability to produce omega-6 (LA) and omega-3 (ALA). These polyunsaturated fatty acids are essential for human health. Their quantities and relative proportions depend on how the microalgae are cultivated.
Various cultivation methods for specific applications
Microalgae can be cultivated using three industrial processes:
- Photo-autotrophy: using light and CO2, this method favors the production of unsaturated fatty acids and balanced omega-6/omega-3 ratios. However, it is not very productive, and therefore costly.
- Mixotrophy: combining light, CO2 and organic carbon sources, this mode increases growth and enables intermediate fatty acid ratios acceptable for human supplementation, but requires additional resources.
- Heterotrophy: in the absence of light, microalgae feed solely on organic carbon, producing ten times more biomass. The resulting lipids are less suitable for human consumption, but useful for industrial applications such as biofuels and biomaterials. This type of microalgae cultivation, known as “fermenting”, is the most profitable.
Optimization and environmental challenges
Controlling cultivation conditions (carbon, nitrogen, temperature) is crucial for controlling the quality and quantity of lipids produced. For example, an excess of carbon and a deficiency of nitrogen favor lipid accumulation to the detriment of cell multiplication. Global warming could also alter the fatty acid profiles of microalgae, impacting the food chain.
Towards the sustainable use of microalgae
The development of this sector depends on a better understanding of the interactions between microalgae strains and their environment. Rational and targeted production, taking into account economic and environmental impacts, will enable us to maximize the value of microalgae in a wide range of sectors. Properly exploited, microalgae could thus become a key lever in meeting tomorrow’s food, energy and environmental challenges.