The Impact of Milk on Black Tea’s Anti-Viral Properties Against SARS-CoV-2


The COVID-19 pandemic, caused by the novel coronavirus SARS-CoV-2, has brought the world to a standstill, prompting extensive research into potential treatments and preventive measures.

Among various approaches, the role of oral tissues, including salivary glands and oral mucosa, in SARS-CoV-2 infection has garnered significant attention [1,2].

This article delves into the importance of oral tissues in viral transmission, the potential of tea as an antiviral agent, and the intriguing influence of milk on black tea’s anti-viral properties.

Oral Tissues and SARS-CoV-2 Transmission

SARS-CoV-2 primarily spreads through droplets and aerosols, often originating from the saliva of infected individuals, whether symptomatic or asymptomatic [3,4,5,6,7,8,9,10].

Speaking, coughing, and sneezing expel saliva into the environment, generating droplets and aerosols that can reach the nasal and oral mucosa of nearby individuals, leading to infection. Understanding the mechanisms of viral inactivation within saliva is crucial for curbing the virus’s spread.

Tea as a Potential Antiviral Agent

In the pursuit of effective strategies to mitigate SARS-CoV-2 transmission, researchers explored various food ingredients that might inactivate the virus.

Notably, tea, including green tea, roasted green tea, oolong tea, and black tea, emerged as a promising candidate for reducing the infectivity of SARS-CoV-2 in vitro [11,12].

The key compound responsible for this effect was (-) epigallocatechin-gallate (EGCG), a tea catechin found abundantly in tea leaves [13].

Additionally, black tea ingredients such as theaflavins (TFs) and theasinensin A (TSA) exhibited similar anti-viral properties, inhibiting the virus by binding to the receptor-binding domain (RBD) of the viral spike protein [11].

The Interplay of Black Tea, Milk, Sugar, and Lemon Juice

Despite the potential of black tea as an antiviral agent, more than 70% of tea production worldwide yields black tea.

Interestingly, epidemiological analyses have not demonstrated a significant negative correlation between black tea consumption and COVID-19 infection rates or severity. However, black tea is often consumed with various additives like sugar, milk, lemon juice, honey, jam, and cinnamon, raising questions about how these ingredients might affect its antiviral properties.

In this study, the focus was on elucidating whether the addition of sugar, milk, or lemon juice could influence the antiviral effect of black tea. Surprisingly, the results revealed that while sugar and lemon juice had no impact, the addition of milk significantly inhibited the antiviral activity of black tea.

Understanding the Inhibitory Role of Milk

Milk, a complex mixture, contains a high concentration of proteins, with caseins accounting for approximately 80% of all milk proteins [26,27]. Caseins consist of four polypeptides: alphaS1-, alphaS2-, beta-, and kappa-caseins. These proteins form large colloidal particles called casein micelles, which are dispersed in milk [26,27,28].

Previous research has suggested that kappa-casein can bind to human rotavirus, rendering it inactive [29]. Casein phosphopeptides derived from various caseins have also been found to stimulate host cells to produce interferon and enhance resistance to certain viruses [30]. However, no prior studies had shown that caseins could bind to tea flavonoids (TFs) and interfere with their antiviral activities.

The Mechanism of Inhibition

It was observed that gTFs, like EGCG, TSA, and TFDG, bind to caseins, potentially leading to a decrease in their antiviral activity.

This interaction between caseins and gTFs might explain why the addition of milk blocked the antiviral effect of black tea. Furthermore, TFs play a crucial role in determining the flavor, bitterness, and astringency of tea, and adding milk to tea is known to reduce these sensations. This reduction in bitterness and astringency could be attributed to the binding of caseins to catechins and TFs.

Practical Implications

For tea drinkers, these findings have practical implications. In the study, even a small volume of milk added to black tea significantly diminished its antiviral activity. For instance, as little as one or two teaspoons of milk (4 to 8 mL) completely nullified the antiviral effect of a standard cup of tea (125 mL). The extent to which milk counteracts black tea’s antiviral properties may vary depending on the tea and milk types.

Concluding Thoughts

While the Omicron subvariants of SARS-CoV-2 continue to pose new challenges due to amino acid substitutions in viral spike proteins, it is noteworthy that black tea appears to inactivate the virus only when consumed without milk. This observation may partially explain why there is no clear negative correlation between black tea consumption and COVID-19 infection rates or severity in different regions.

In conclusion, incorporating black tea without milk into the diet of infected individuals may help attenuate viral spread, potentially benefiting both the infected person and those in close proximity. Clinical studies are necessary to further investigate these possibilities and provide valuable insights into the potential role of tea as a preventive measure against SARS-CoV-2 transmission.

The world continues to grapple with the challenges posed by COVID-19, but through ongoing research and exploration, we may uncover simple yet effective strategies to mitigate its impact on society.

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