Researchers at the Technical University of Denmark and Aarhus University used a two-stage fermentation to raise an essential amino acid in plant proteins, aiming at better organic animal feed and more nutritious plant foods.

Plants are an increasingly important source of protein, for people trying to eat less meat and for farmers looking to replace imported soy in animal feed. But plant proteins have a nutritional weakness. Most fall short on one or more of the amino acids that animals, including humans, must get from food.

Researchers at the Technical University of Denmark (DTU) National Food Institute and Aarhus University report a way to fix that using microbes. In a study published in the Journal of Agricultural and Food Chemistry, they describe a fermentation process that more than tripled the content of the essential amino acid lysine in faba beans and rapeseed press cake.

“Plant proteins do not contain the right amino acids in sufficient quantities to be an ideal source of nutrition for humans,” said Christian Solem, an associate professor at the DTU National Food Institute. “Our solution is to use microorganisms to enrich plant-based foods with essential amino acids and important vitamins.”

The amino acid gap

Proteins are built from 20 amino acids. The human body can make some of them, but nine, known as essential amino acids, must come from the diet. A protein is considered complete when it contains all nine in adequate amounts.

Animal proteins such as meat, eggs and milk are generally complete. Many plant proteins are not. Cereal grains such as wheat and rice are typically low in lysine, while legumes such as beans tend to be low in the sulfur-containing amino acid methionine. That is one reason traditional diets often pair grains with legumes, as in rice and beans.

The researchers say their approach could help address malnutrition in low-income countries, where diets dominated by a few plant staples can leave people short of essential nutrients.

Two microbes, two jobs

The team developed a two-stage fermentation process. In the first stage, a bacterium called Bacillus subtilis subsp. natto breaks down the proteins in faba beans and rapeseed press cake into smaller pieces, releasing nitrogen sources.

That strain is familiar to many people in Japan. It is the bacterium used to make natto, a traditional dish of fermented soybeans known for its strong flavor and sticky, stringy texture.

In the second stage, a different bacterium, Corynebacterium glutamicum, uses those nitrogen sources to produce lysine. C. glutamicum is a workhorse of industrial biotechnology. It was discovered in Japan in the 1950s for its ability to produce glutamate, the basis of the flavor enhancer MSG, and strains of it are now used to manufacture large quantities of amino acids, including lysine for animal feed.

After fermentation, lysine content rose 3.4-fold in faba beans and 3.6-fold in rapeseed meal, reaching 37.5 and 29 grams per kilogram of dry matter, respectively.

The microbes bring a second benefit. “The interesting thing is that we can use microorganisms to improve the amino acid profile of plant-based ingredients while also making plant proteins easier to digest by partially breaking them down,” Solem said. “This is particularly beneficial because many crops contain antinutrients that make it harder for our bodies to absorb the nutrients found in plant-based foods.”

Northern European crops

The team focused on faba beans and rapeseed press cake because both are grown in large volumes in Denmark and northern Europe, although the technique also works with other crops.

Faba beans, also called fava or broad beans, are rich in protein and are used in both animal feed and human food. Rapeseed press cake is the protein-rich material left over after oil is pressed from rapeseed, the crop grown for canola oil. Both could replace imported soy in animal feed, reducing Europe’s dependence on soybeans grown largely in the Americas.

A problem for organic farms

The work is part of a project called NextOrganic, which focuses on animal feed. A shortage of essential amino acids in feed slows animal growth and can cause illness. Conventional farmers usually address this by adding amino acids made by industrial fermentation, or by feeding extra protein.

Organic farmers have fewer options. “In organic pig and poultry production, it is not permitted to add synthetic amino acids to the feed, so overfeeding with protein is the only option,” said Jan Værum Nørgaard, a professor in the Department of Animal and Veterinary Sciences at Aarhus University.

That has environmental costs. “If the animals are given more protein than they can utilise, they excrete more nitrogen via urine and faeces, which places a strain on the environment,” Nørgaard said. Excess nitrogen from livestock farming contributes to water pollution, algal blooms and emissions of ammonia and nitrous oxide, a potent greenhouse gas.

Feed with a better balance of amino acids would let animals make better use of their protein, cutting waste and nitrogen pollution.

More amino acids to come

“We have demonstrated the principle using the essential amino acid lysine and will soon have solutions ready that will also allow us to enrich crops with two other essential amino acids,” Solem said.

The release does not report feeding trials, so it is not yet known how the fermented ingredients perform in animal diets, how they taste or how the process would be scaled up, or whether organic certification rules would accept amino acids produced by microbes inside the feed. The work was funded by Denmark’s Green Development and Demonstration Programme (GUDP).

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Notes

1. “A Novel and Simple Fermentation Approach for Adjusting the Amino Acid Composition in Plant Biomasses to Enhance Nutritional Value for Humans and Animals.” Journal of Agricultural and Food Chemistry, 12 August 2026. DOI: 10.1021/acs.jafc.6c06318.
2. Technical University of Denmark. “Bacteria can make plants healthier for humans and animals.” EurekAlert!, 30 September 2026. https://www.eurekalert.org/news-releases/1146060.

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