WUR researchers examine tomato leaves, insects and fungi as “protein transition” options

30 May 2022 --- Scientists at Wageningen University & Research (WUR) in the Netherlands are urgently studying viable options to initiate a “protein transition” that will reduce the competition between humans and animals for food and usher in sustainable production on a mass scale.

The challenge these researchers have set is to find ways to increase the availability and diversity of emerging protein sources such as tomato leaves, fungi and insects that are accepted by a large portion of the population.

While these protein sources are already known and used in food production, the scale is not yet sufficient to feed the masses. Also, they have not been accepted entirely by people and the challenges of these sources need to be ironed out. 

For example, extracting protein from tomato leaves is cumbersome; it is labor-intensive to produce the necessary quantities of insect protein and fungi do not yield the right amounts of necessary protein.

Rubisco protein from plant leaves
High protein crop residues from the leaves of plants are valuable to a certain degree. These are often not extracted, are composted or used as animal feed.  

The leaves of all plants, such as those of sugar beet or tomato plants, contain the protein rubisco. 

“At least a quarter of all the protein in the leaf is rubisco. This protein is essential for capturing and storing CO2 from the atmosphere. It’s readily soluble and not attached to anything else in the cell, so you can squeeze it out of the leaf,” says Marieke Bruins, senior scientist, protein technology, WUR.The extraction of rubisco protein from tomato leaves is being analyzed by WUR researchers.  

The disadvantage of tomato leaves is they also contain toxins. WUR scientists have developed a patented process for extracting protein from leaves and are testing to see if the process prevents toxins from entering the final product. Cosun, a beet producer, is currently using the method to extract protein from sugar beet leaves. 

One advantage of rubisco protein is that it can be quickly processed into a gel. Producers add eggs to achieve the desired structure, which might be helpful in the production of meat substitutes or plant-based dairy products; however, those will not be vegan. 

“That’s not a quality you typically find in many other plant-based proteins, such as soy. The only other plant-based protein that can make a good gel is potato protein,” says Bruins. 

“We want to find the right balance, which might be 10% rubisco protein for the gelling properties, supplemented with cheaper protein like soy for its nutritional value,” explains Bruins.

“Crops like tomatoes and sugar beet were originally developed for their primary product: the beet itself and the tomato. We want to see if we can make adaptations that optimize secondary protein extraction from the leaves of these crops too. It’s less about the absolute amount of protein and more about the proportion we can extract. Because we’re only using a small proportion right now,” she adds.

Insect proteins have regulatory approval
Insects have been identified as having the potential to significantly contribute to the “protein transition” because they can be reared on residues and then processed into products that both people and animals can eat. 

Rearing insects on a large scale for protein production is still challenging as yields fluctuate. 

“We can’t keep using soy to feed our growing population of farm animals. Insects have a similar nutritional value, but they’re more sustainable because they don’t require much land or water, and they can be reared on residues,” says Esther Ellen, project leader, insect breeding, WUR. 

In the EU, insect protein has been approved for animal feed for poultry and pigs. A few insect products have been approved for human consumption. 

Breeding systems could play a key role in scaling up insect protein production. WUR breeding programs are trying to determine whether genetic selection could improve protein production in insects. 

Insect breeding is still in its infancy, but WUR researchers are satisfied that the challenges are already being addressed scientifically.

“For example, we don’t want to select for production alone. We also want to think about inbreeding, health and welfare. We have an opportunity to establish good practice early on and learn from experiences of breeding in traditional livestock farming,” Ellen adds.WUR researchers aim to produce produce from fungi with renewable forms of biomass.

Viability of scaling fungi
Mushroom-forming fungi, known as basidiomycetes, found in the mycelium network of the plant, is a potential sustainable protein source. Usually, the fungi are discarded. The research into this is limited. 

Unlike existing types of fungal proteins such as tempeh or Quorn, which are cultivated on substrates suitable for human consumption, WUR scientists hope to produce proteins from renewable forms of biomass that have not previously been used in this way. 

“As a bonus, you don’t need any additional land because you can grow them in buildings. And suppose you grow only the mycelium and therefore don’t have to wait for the mushrooms to appear. In that case, you have a shorter production cycle,” says Karin Scholtmeijer, research associate, plant breeding. 

“These fungi have the advantage of being able to grow on lignocellulose, which is something that few other organisms can do,” she says.

Lignocellulose is a woody material found in all plants and is the most significant renewable type of biomass. 

“The fungi also produce a lot of free amino acids, which is useful in terms of nutritional value because these are easily absorbed in the intestine,” says Scholtmeijer.

Other healthy components in the fungi include fiber, vitamins B and D, and components that boost the immune system. They also come in various textures, aromas, colors and flavors.

By Inga de Jong