In the poem "I ask you," poet Ahn Do-hyun asked, "Do not carelessly kick coal briquette ash with your foot/Have you ever been a person burning hot for anyone?" Now we should also say not to carelessly throw away okara, the tofu-making residue. Have you ever once tried to capture greenhouse gases?
Scientists at the Swiss Federal Institute of Technology Zurich announced in the Proceedings of the National Academy of Sciences on the 11th (local time) that they developed a material that directly captures carbon dioxide from the air using food waste left over from making cheese and tofu. According to the team, the carbon dioxide capture efficiency using food waste jumped by up to 50% compared with existing technology.
Carbon dioxide is a greenhouse gas that causes global warming. In 2015, 195 countries, including Korea, signed the Paris Agreement and agreed to reduce greenhouse gas emissions to keep the global average temperature from rising more than 1.5 degrees Celsius above preindustrial levels. The best method is to remove carbon dioxide directly from the air, but the heavy energy demand has kept it from practical use.
◇ Cheese and tofu residues turn into sponges that trap carbon
A team led by Professor Raffaele Mezzenga in the Department of Materials at the Swiss Federal Institute of Technology Zurich processed food waste generated during cheese and tofu production into protein beads. The protein beads efficiently bound and then released carbon dioxide with only small amounts of energy.
Whey left over from cheese making and okara, a tofu byproduct, are rich in protein. According to the National Standard Food Composition Table, 100 g of okara contains 4 g of protein. That is less than the 9.62 g in 100 g of tofu, but still a substantial amount. The researchers separated protein from waste in the cheese and tofu production processes and formed long, threadlike chains called amyloid fibrils. When they injected potassium hydroxide, they produced beads 0.5–1 cm in diameter.
In experiments, the protein beads extracted 0.097 g of atmospheric carbon dioxide per 1 g of beads. That means with just 1 kg of protein beads, about 100 g of carbon dioxide can be separated. The team said this result is 10%–50% better than existing direct air capture (DAC) technologies.
Potassium hydroxide is what extracts carbon dioxide from the protein beads. Potassium hydroxide is a strong base, and when it encounters carbon dioxide, an acidic oxide, it immediately triggers an acid-base neutralization reaction to form carbonate and water. The protein obtained from cheese and tofu waste serves as a support that holds potassium hydroxide so it does not run off or clump, allowing it to contact air over a large surface area. Mezzenga said, "The protein beads are like a sponge that, through potassium hydroxide, absorbs large amounts of carbon dioxide."
◇ Easy carbon release, and materials can be recycled
Conventional DAC methods require applying heat and a vacuum, a pressure lower than ambient, to the carbon sorbent to release carbon dioxide again. That allows the carbon dioxide to be stored or converted into other substances, but the process consumes a lot of energy. Then the costs outweigh the benefits and the economics suffer.
Mezzenga said the carbon dioxide sorbent made from food waste also has advantages here. At room temperature, alternating sprays of weak acid and base onto the protein beads for about 10 minutes break the chemical bonds so carbon dioxide can be separated again. The team said the acid and base used at this time, as well as the protein beads, can be reused afterward.
Zhou Dong, the first author of the paper, said, "Synthetic materials currently used for carbon dioxide capture degrade quickly, but the protein beads we made remain stable for a long time." The researchers said they repeated adsorption and release of carbon dioxide 30 times in the lab without any drop in efficiency.
Of course, the protein beads also need to be replaced after thousands of uses. Mezzenga said these can also be recycled. Because the composition is protein, they can be used as agricultural fertilizer or converted into biofuel, the team explained. He added that since the materials are food grade and nontoxic, they cause less environmental pollution than other carbon dioxide capture methods.
The researchers are scaling up experiments to commercialize the carbon-trapping protein beads. They said they separated up to 50 g of carbon dioxide in the lab using only a few grams of protein beads. While they have not yet calculated the exact capture expense per metric ton of carbon dioxide, they expect it to be much lower than existing technologies.
References
PNAS (2026), DOI: https://doi.org/10.1073/pnas.2535689123