Compared to spirulina — a similar organism that’s been popular as a food and feed supplement for half a century — the microalga Galdieria is cheaper and easier to grow, and even more nutritious. In a closed-circuit reactor, it can convert organic waste into valuable proteins. Those are the conclusions of the PhD research of Fabian Abiusi of the group Bioprocess Engineering at Wageningen University & Research.
“Microalgae-based products have been around for a long time,” says Mr. Abiusi, a biotechnologist originally from Italy, “but in general, they are costly to produce. When these algae are grown in the dark, they convert only half of their organic substrate into biomass. And when they are grown under illumination and use carbon dioxide, they generally yield only low biomass densities. Both strategies require a costly system for efficient gas exchange. In my PhD research, I developed a new cultivation method for microalgae that doubles productivity while halving the production costs.”
The trick, Mr. Abiusi explains, is growing the microalgae in a mixotrophic photobioreactor: a reactor that provides its algae with light as well as an organic substrate such as sugar. Microalgae, like all plants, use sunlight as an energy source to convert carbon dioxide into organic molecules and oxygen. This is photosynthesis. In the dark, however, the opposite happens: plants use oxygen and organic molecules and release carbon dioxide. Industrial fermentation uses this latter principle to produce various biomolecules, such as proteins, medicines or alcohol from an organic substrate.
“In those processes, usually only half of the organic carbon is converted into biomass, while the other half is lost as carbon dioxide”, says Mr. Abiusi. “However, in a mixotrophic photobioreactor, you can couple the production of oxygen via photosynthesis to the consumption of oxygen in the cell’s metabolism. Similarly, almost all of the carbon dioxide produced by the microalgae is used again by the photosynthesis, making this process almost carbon neutral, and very efficient. You have double productivity, without the need for electric energy for aeration or carbon dioxide.”
The Next Superfood?
As an added bonus, Galdieria turns out to be much richer in protein than spirulina. Mr. Abiusi and colleagues discovered this by unravelling the full profile of the microalga’s amino acids — its protein building blocks. “Two thirds of Galdieria’s dry weight are amino acids”, says Mr. Abiusi, “which is more than is the case for meat, milk, cheese and eggs.”
Specifically, the microalga contains much cysteine and methionine, two sulphur-containing amino acids, which it owes to its evolution in sulphur-rich volcanic springs. “These amino acids are limited in plants, which is one of the reasons that it is difficult for us to derive well-balanced nutrition from a plant-based diet.”
Galdieria may be the next superfood, according to Mr. Abiusi. It has the potential to help feed the world, improve human health, transition to a more plant-based diet, reduce energy use, and make good use of organic waste. “We now have a proof of principle,” concludes the bio-engineer. “I’m working with a start up in Wageningen, called Algreen, to optimize and scale up the process, using food waste as a substrate. We expect approval by the European Food Safety Authority in the course of next year. In a few years’ time, you’ll find Galdieria products on the market, I have no doubt about that.”
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