TOKYO -- An enzyme found in natto, a Japanese food made from fermented soybeans known for its strong smell, hinders infection with the coronavirus, researchers in Japan have found.
Researchers from Tokyo University of Agriculture and Technology and other institutions, who made the discovery, say it is extremely rare to directly confirm that food constituents have antiviral properties. It remains unclear, however, whether eating natto can prevent infections, as the experiment was conducted with cultured cells.
Infection with the coronavirus occurs when spike proteins on the surface of the virus become attached to certain receptors on parts of human cell walls known as angiotensin-converting enzyme 2 (ACE2) receptors. Meanwhile, natto bacteria, which is used to ferment soybeans, is said to improve the intestinal environment and boost immune strength.
The researchers focused on an enzyme secreted by natto bacteria that breaks down proteins. The team combined the coronavirus strain that first spread in China with a natto extract in a test tube and applied this to cultured cells to examine whether the treated virus infected the cells.
They found that the extract constituents broke down the spike proteins on the virus's surface, and because of this, the cultured cells did not become infected. However, the protein-degrading enzyme is inactivated when heated, and when researchers heated the mixture to a certain temperature, it was no longer possible to prevent infection. Researchers therefore concluded that one or more enzymes, or protease, had destroyed the surface of the virus, and prevented the cells' infection.
Similar results were confirmed with the allegedly more transmissible N501Y variant of the coronavirus first reported in the United Kingdom. Researchers also discovered that the natto extract prevented infection of the cells with bovine herpesvirus 1 (BHV-1), which can cause respiratory tract disorders in cattle.
Research team member Tetsuya Mizutani, of the Tokyo University of Agriculture and Technology, commented, "Further verification is needed to determine whether it could be a method to prevent an increase in the number of infected people if there are antiviral properties in the food product."
The results of the study were published online on July 13 in the international academic journal Biochemical and Biophysical Research Communications.
(Japanese original by Ayumu Iwasaki, Science and Environment News Department)