Tomato leaves: a new alternative protein source?
Tomato leaves boast an excellent protein content. Can they be the next alternative protein source? Scientists are studying them.
Published on July 19, 2025
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Did you know that tomato leaves are very high in protein content? They have a protein content of up to 27%, comparable to that of ground beef. Researchers at Wageningen University & Research (WUR) were the first in the world to extract high-value protein from tomato leaves, a significant waste stream of greenhouse horticulture.
Much of this protein consists of Rubisco, an enzyme essential for photosynthesis, which enables plants to capture carbon dioxide from the air. This protein is thus found in every green plant. In its purest form, Rubisco has a neutral aroma, colour, and flavour, and a good balance of the essential amino acids. This makes it a potentially functional protein for developing new plant-based alternatives, providing an enhanced mouthfeel and a firm bite. Yet, the way to our tables is still far away.
Tomato leaves protein extraction hurdles
Research by WUR research candidate Marietheres Kleuter highlighted some of the obstacles that still need to be overcome to make tomato leaves a usable protein. “Ideally, you can turn this protein into a dish similar to tofu. But that’s a way off. In our experiments, the extracted protein remained green due to the chlorophyll. Which isn’t ideal - people aren’t used to green protein - but if you use it in shakes or as a dietary supplement, for example, the colour is less of a problem,” she said.
In 2022, WUR scientists extracted high-value Rubisco protein from tomato leaves using methods similar to those developed for extracting Rubisco from sugar beet leaves. This process filters out smaller components, including toxins, resulting in a high-value, toxin-free protein powder.
One of the primary hurdles is the difficulty in extracting the protein due to the physical barrier formed by the cell walls in tomato leaves. Additionally, the protein composition changes as the leaves mature, resulting in a reduced protein yield. Enzymes called proteases break down proteins into smaller peptides as the leaves age, further complicating extraction efforts.
To combat this, researchers have explored turning off genes responsible for protease production, which showed promise in inhibiting protein degradation towards the end of the growth period. Further proteomics analysis has identified more genes involved in protein content and extractability, offering insights for breeding new tomato varieties with higher, more stable protein levels.
The quest for sustainable protein sources
As the world population grows, and given the high climate impact of producing animal-origin protein, the need for more sustainable protein sources is as pressing as ever. To this extent, the WUR is exploring several sources, including duckweed.
Also known as water lentils, duckweed has been approved by the European Food Safety Authority (EFSA) as a novel food for production and consumption in the EU. It can double its biomass every 48 hours under optimal conditions and contains up to 40% protein by dry weight. WUR researchers forecast the first duckweed-derived products to be on supermarket shelves by 2028.
In the United States, the California-based startup Plantible Foods has already raised $30 million to expand the production of its duckweed-derived protein, Rubi Protein. Like tomato leaves, duckweed represents a promising step towards a more sustainable and plant-based future.
