"Proteases are important to the health and viability of cells and viruses. If proteases are inhibited, cells cannot perform many important functions - like replication, for example," said study author De-Yu Xie from the North Carolina State University  in the US "One of our lab's focuses is to find nutraceuticals in food or medicinal plants that inhibit either how a virus attaches to human cells or the propagation of a virus in human cells," Xie added.

In the study, published in the journal Frontiers in Plant Science, the research team performed both computer simulations and lab studies showing how the so-called "main protease" (Mpro) in the SARS-CoV-2 virus reacted when confronted with a number of different  plant chemical compounds already known for their potent anti-inflammatory and antioxidant properties.

"Mpro in SARS-CoV-2 is required for the virus to replicate and assemble itself. If we can inhibit or deactivate this protease, the virus will die," Xie said.

Computer simulations showed that the studied chemical compounds from green tea, two varieties of muscadine grapes, cacao powder and dark chocolate were able to bind to different portions of Mpro.

"Mpro has a portion that is like a 'pocket' that was 'filled' by the chemical compounds. When this pocket was filled, the protease lost its important function," Xie explained.

Lab experiments also showed similar results. The chemical compounds in green tea and muscadine grapes were very successful at inhibiting Mpro's function; chemical compounds in cacao powder and dark chocolate reduced Mpro activity by about half.

"Green tea has five tested chemical compounds that bind to different sites in the pocket on Mpro, essentially overwhelming it to inhibit its function," Xie said.

"Muscadine grapes contain these inhibitory chemicals in their skins and seeds. Plants use these compounds to protect themselves, so it is not surprising that plant leaves and skins contain these beneficial compounds," the author noted.