**1.1 Green tea can kill bacteria**


## **1.2 Green tea composition**

The medically important components of green tea are the polyphenols, most importantly the flavonoids. The main flavonoids in tea are the catechins, making up 30–40% of the water-soluble solids in green tea [3, 11]. The different types of tea vary in the amount of catechins that they contain, with green tea containing the most, then Oolong tea, then black tea. The initial steaming process in the production of green tea destroys the enzyme polyphenol oxidase, thus protecting the polyphenol content. There are four main catechins in tea: (-)-epicatechin (EC), (-)-epicatechin-3-gallate (ECG), (-)-epigallocatechin (EGC) and (-)-epigallocatechin-3-gallate (EGCG). In green tea, EGCG is the most abundant, representing approximately 59% of the total catechins. EGC is next, making up approximately 19%, then ECG, at 13.6% and EC, at 6.4% [6, 10].

Green tea contains less caffeine than coffee, but enough to produce an effect. It also contains the amino acid L-theanine, which can work synergistically with caffeine to improve brain function [8].

Multiple studies show that the catechin compounds in green tea can have various protective effects on neurons in test tubes and animal models, potentially lowering the risk of Alzheimer's and Parkinson's [15].

#### **1.3 Black, green and white**

Black, green and white teas are the most popular beverages worldwide [16].

Tea leaves are known for its antibacterial activity against any microorganisms. It is one of the most popular beverages worldwide.

Black tea has a long history of use dating back to China approximately 5000 years ago. It is made from the dried leaves of *Camellia sinensis*, a perennial evergreen shrub formerly known as *Thea sinensis*. It is native to southeastern Asia. Green tea, black tea, and oolong tea are all derived from the same plant. Black tea results from the oxidation of *Camellia sinensis* leaves.

The chemical components in tea include alkaloids (theobromine, caffeine, theophylline), polyphenols, amino acids, polysaccharides, volatile acids, vitamins, lipids as well as inorganic elements [17–19]. Black tea is used for treating headaches, low blood pressure, preventing heart disease, including atherosclerosis and heart attack, preventing Parkinson's disease, reducing the risk of stomach and colon cancer, lung, ovarian and breast cancers [20].

Currently, a growing consumption of tea is observed in western countries, where it has been considered as functional food.

Nutritional Value of Black Tea Like other types of tea, black tea contains:


Black tea also contains catechins (the powerful antioxidants in tea that fight cancer-causing cells and help prevent heart disease), tannins (the naturally occurring chemical compounds that give black tea and red wine their astringency), guanine (a natural stimulant) and xanthine (another natural stimulant, similar to caffeine).

The many antioxidants and polyphenols in black tea are associated with a number of health benefits. Specifically, black tea contains complex flavonoids, which are polyphenols that aid in disease prevention. A single cup of black tea contains an average of 200 mg of flavonoids. Many doctors now recommend getting 600 mg of flavonoids per day for a range of health benefits. The flavonoid polyphenols in black tea known as thearubigin and theaflavin act as especially powerful antioxidants. Interestingly, these two flavonoids are more concentrated in black tea than in green tea [21].

Additionally, black tea is low in sodium and calories (if you do not add a sweetener). Plus, black tea has a bold flavor, making it a good substitute for those accustomed to soft drinks other unhealthy beverages (which also tend to have bold flavors) [22].

### **2. The biological properties of tea**

The biological properties of tea include effects on the Central System (CNS) and antioxidant effects, attributed to the presence of methylxanthines, such as caffeine and phenolic compounds, especially catechins [23].

Black tea is more oxidised than all other types of teas. It contains antioxidants and other substances that might help protect the heart and blood vessels. It is also used for treating headache and low blood pressure; preventing heart disease, including "hardening of the arteries" (atherosclerosis) and heart attack [24].

## **3. Black tea fights diseases and infections; how black tea benefits**

The tannins in black tea do not just give it its characteristic taste. Several studies have shown that tannins help fight viruses such as influenza ("the flu"), dysentery, and hepatitis. Black tea also contains alkylamine antigens, which help boost immune response [25]. Both Iranian non fermented (green tea) and fermented (black tea) have anti *Streptococcus mutans* activity in vitro. The anti-*Streptococcus mutans* activity of black tea appears on a lower concentration than green tea [18].

Black and green tea have antibacterial activity against many pathogens.

Effectiveness of aqueous extract of green, black and red tea leaves against some types of Gram positive and negative bacteria [19].

An *in vitro* study recorded that the black tea has antibacterial activity to the following pathogens:


All tea extracts have shown significant antibacterial activity against *S. aureus* ATCC 25922 with Aqueous extract of Green tea exhibiting highest activity. All Green tea extracts exhibited significant activity against *E. coli* ATCC 25923 higher than Black tea extracts. As compared to Green tea extracts, Black tea extracts showed much lower activity against *P. aeruginosa* ATCC 27853. *S. aureus* was found to be most susceptible to tea extracts followed by *E. coli* and *P. aeruginosa*. Green tea and Black tea extracts have shown significant antibacterial activity with former being more effective than later. In future there is immense potential of clinical application of polyphenolic contents of tea extracts as adjuvant therapeutic agents to tackle the menace of growing antibiotic resistance [20, 23].

Black tea extract also had the ability to completely inhibit *Pseudomonas* growth on blood agar and inhibited protease activity and adhesion. There were also differences in Congo red binding seen in bacterial cell suspensions cultured in growth media that contained tea extract. The synergistic activity of tea extract with antibiotics has changed the resistance of *P. aeruginosa* (without the tea) to sensitive (in the presence of tea extract) [22].
