L'approvisionnement alimentaire mondial est confronté à une série de menaces, notamment le changement climatique, les guerres, les ravageurs et les maladies. Un organisme trop petit pour être vu par l'œil humain, les microalgues, pourrait offrir certaines réponses.

Nourrir une population mondiale croissante qui, selon les prévisions des Nations Unies, atteindra 9,8 milliards d'ici 2050, et la nécessité de conserver les ressources naturelles pour les générations à venir peuvent sembler contradictoires au premier abord.

Mais une solution, bien qu'elle ne soit pas encore en vue, n'est certainement pas hors de portée. Les scientifiques européens ont récemment développé un appétit pour les microalgues, également appelées phytoplancton, un sous-groupe d'algues constitué de micro-organismes photosynthétiques unicellulaires.

La plupart des gens connaissent la plus grande forme d'algues, de varech ou d'algues. Il peut mesurer jusqu'à trois mètres de long et, sous certaines formes, est un mets bien connu. Les microalgues apparentées, que l'on trouve à la fois dans l'eau de mer et dans l'eau douce, ont attiré l'attention des chercheurs en raison de leurs propriétés extraordinaires.

Ces organismes microscopiques peuvent être utilisés pour l'alimentation animale, notamment en aquaculture, et divers aliments dont les pâtes, les saucisses végétaliennes, les barres énergétiques, les produits de boulangerie et les crèmes végétales.

La plupart des cultures commerciales de microalgues se concentrent sur la production de biomasse séchée telle que la chlorella ou la poudre de spiruline en tant qu'aliment offrant des avantages considérables pour la santé. Certaines souches de microalgues accumulent non seulement jusqu'à 65 à 70 % de protéines, mais sont également des sources durables d'acides gras oméga-3, une substance traditionnellement dérivée principalement du poisson et de l'huile de poisson.

Des composés bioactifs supplémentaires, tels que les vitamines B12, K ou D, signifient que les microalgues contiennent des propriétés importantes pour la santé, réduisant potentiellement le risque de cancer et de maladies cardiovasculaires.

Algues du désert

"Les microalgues peuvent être cultivées dans de nombreux endroits différents, dans des conditions très différentes", a déclaré Massimo Castellari, qui est impliqué dans le projet ProFuture financé par Horizon visant à intensifier la production de microalgues. "Nous pouvons le cultiver en Islande et dans un climat désertique."

Les technologies de culture intensive des microalgues sont en développement depuis les années 1950.

Aujourd'hui, les microalgues sont cultivées dans des photobioréacteurs en système ouvert ou fermé, qui sont des cuves conçues pour contrôler la production de biomasse. La version à système fermé, bien que plus coûteuse à construire, offre plus de contrôle sur les paramètres expérimentaux et moins de risque de contamination.

La substance n'est en aucun cas un simple complément alimentaire à la mode. Par exemple, au Tchad, pays enclavé à faible revenu, la consommation de spiruline récoltée dans le lac Tchad a considérablement amélioré l'état nutritionnel des populations car la spiruline est une excellente source de protéines et de micronutriments.

On top of its nutritional value, microalgae offer climate benefits by sequestering carbon dioxide as well as economic advantages by using farming areas more efficiently and—through the use of non-arable land—expanding the possibility of biomass production.

With a total of less than 57,000 tons cultivated in 2019, according to the UN Food and Agriculture Organization (FAO), production of microalgae is still very much in its early stages. By comparison, primary-crop output was 9.4 billion tons in 2019.

Food inflation

Russia's continuing war in Ukraine has highlighted just how vulnerable global food supply can be. Halts to Ukrainian grain exports and increases in energy prices have helped push food inflation around the world to record highs, with developing countries being hit disproportionately hard. In May this year, costs for food had risen by 42% compared with 2014–2016, the UN reported.

Last year, as many as 828 million people were affected by hunger—an increase of roughly 46 million compared with 2020 and a surge of 150 million since the outbreak of the COVID-19 pandemic.

The FAO projects that some 670 million people will still face hunger by the end of the decade.

While the benefits of cultivating organic microalgae for food and feed are substantial, market growth will require overcoming obstacles including a lack of automated production in the industry, according to Castellari, who works at the Institute of Agrifood Research and Technology in Barcelona, Spain.

"The automatization is still not completely implemented," he said. "There are small producers in Europe—many steps still involve manual labor. So they are still working on optimizing the process."

Processed biomass

The challenges go well beyond cultivation. With microalgae, biomass has to be processed, cleaned and dried before a usable powder can be obtained. The next step is to scale up production to drive down costs.

In addition, there are regulatory challenges. Only a few species of microalgae are currently authorized in the European Union.

"In Europe it's still in a preliminary stage of development," said Castellari. "There are thousands of species of microalgae, but for food consumption or feed there are only seven species authorized."

To gain knowledge about the possibilities to use other species, Castellari and his team are also investigating these other kinds of microalgae.

Due to these challenges, the portfolio of products containing microalgae remains limited today. But, if these hurdles can be overcome, the overall prospects for the microalgae industry are promising. Besides being a source of food and feed, the plant can be used for biofuels, cosmetics, fertilizer and health supplements.

Astaxanthin, a blood-red pigment extracted from algae, already has notable uses. A powerful antioxidant, astaxanthin can be found in seafood and is commonly used to color shrimp. It is also sold in the form of pills as a food supplement.

Astaxanthin is thought to have potentially a positive impact on brain function, athletic performance and aging skin, among other things.

Matteo Ballottari, associate professor of biotechnology at the University of Verona in Italy, helped start the European Research Council's Horizon-funded project AstaOmega simultaneously to produce astaxanthin and omega-3 fatty acids in microalgae for aquaculture and human nutrition.

Quality and quantity

Most omega-3 supplements are derived from fish oils. This, however, raises sustainability concerns such as damage to marine ecosystems as a result of overfishing.

"There is more demand for eating high-quality foods, along with an awareness for incorporating omega-3 rich ingredients in our diets," Ballottari said. Responding to this trend while feeding a growing world population is 'a big challenge," he said.

Meanwhile, on the astaxanthin front, the AstaOmega researchers have made progress. They have been able to obtain a new strain that can produce astaxanthin on its own, without needing to be "stressed." This means the researchers don't have to change production parameters such as light intensity, temperature or nitrates concentration. Also, extracting the substance has become easier, resulting in lower costs.

Scientists agree that microalgae have the potential to change the ways in which we eat for the better.

"Microalgae can help us to increase the protein production within Europe to reduce our dependence on other countries," said Castellari of the ProFuture project. + Explorer plus loin

Large-scale cultivation of microalgae can clean emissions from industry, can also be used in Nordic climate