Japanese researchers set out to explore various foods and ingredients that may inactivate the strain of SARS-CoV-2 responsible for COVID-19.
The COVID-19 virus primarily spreads through the saliva of infected individuals, including asymptomatic carriers. Saliva containing the virus is released when talking, sneezing, or coughing, forming droplets and aerosols that disperse into the air.
Professor Osam Mazda and his research team at Kyoto Prefectural University of Medicine in Japan believe that inactivating the virus in saliva is crucial for preventing COVID-19. Therefore, they explored various foods and ingredients that may inactivate the strain of SARS-CoV-2 responsible for COVID-19. A previous study they conducted found that polyphenols found in green tea or black tea reduced the infectivity of the virus in human saliva in vitro, demonstrating virus-inactivating properties. The polyphenols in tea can bind to the spike protein of the virus, preventing it from infecting cells.
The research team published their new study on Oct. 3 in Scientific Reports, indicating that green tea, matcha, and black tea rapidly and effectively inactivated some Omicron subvariants.
One of the experiments in the study involved seven healthy volunteers who consumed candies containing green tea, black tea, or no tea components, and their saliva subsequently collected. Researchers found that saliva collected immediately after consuming candies containing green or black tea had high concentrations of tea polyphenols, including epigallocatechin gallate (EGCG) and theaflavin digallate. When researchers mixed saliva samples with the early Omicron virus strain BA.1 for 10 seconds, they observed rapid inactivation of the virus by saliva containing tea polyphenols. However, the virus-inactivating effect gradually diminished between 5 and 15 minutes after the cessation of the candy.
The research team believes that if infected individuals consume candies containing green tea or black tea, it may be useful in inactivating the virus, decreasing the virus load in the oral and gastrointestinal tracts, and preventing the virus from spreading to nearby non-infected individuals.
Another experiment involved steeping black tea, green tea, or matcha in hot water and subsequently mixing the virus suspension with the tea beverages for 10 seconds, followed by assessing the virus's virulence. The results revealed that the infectivity of the BA.1 and other Omicron subvariants decreased to less than one percent.
Not only does freshly brewed tea have virus-inactivating effects, but bottled green tea beverages purchased from grocery stores also significantly reduced the infectivity of Omicron subvariants BA.1, BA.5, and BQ.1.1, although they were not effective against BA.2.75.
The study also found that different Omicron subvariants have varying sensitivity to tea polyphenols. For instance, EGCG at a concentration of 1000 μM can inactivate more than 99 percent of the BA.1 and BA.5 viruses. However, the BA.2, BA.2.75, XBB.1, and BQ.1.1 viruses remained infectious at the same EGCG concentration.
Black tea, produced by oxidizing green tea leaves, exhibits a vibrant reddish-orange color due to the transformation of tea polyphenols into theaflavins in the tea leaves. The researchers treated various Omicron viruses with theaflavin concentrations similar to those found in black tea and observed a significant reduction in the virulence of BA.1, XE, BA.5, XBB.1, and BQ.1.1 viruses. However, the same theaflavin concentration had little effect on BA.2 and BA.2.75.
The research also found that the antiviral mechanism of EGCG is to render the virus inactive, and when used to treat cells, it does not induce anti-virus effects in the cells.
The research team had previously suggested that holding tea in the mouth for 10 seconds before swallowing it while dining in a restaurant could temporarily inactivate the virus in...
