**3.1 History**

The history of tea drinking started in 2737 BC. AD, according to Chinese tradition, when Emperor Shen Nong, a skilled ruler and scientific trained, discovered tea by mistake [11, 12]. *Camellia* species have spread from Nepal to Taiwan. Japan in East Asia has more than 90 species, tea is the most distributed [13, 14].

Green tea is very popular in East Asia (especially in China and Japan), while black tea is in the West. The use of tea leaves probably began in southwestern China over 3000 years ago. It was initially used only for chewing and drinking, much like using coffee for the first time [15]. The origin of the tea plantation was estimated by Sealy [16] around the Chinese Yunnan district, but it is not confirmed. Wild form of the Assamica variety of *C. Sinensis* was discovered in India in 1835, then in Thailand and Burma [17, 18].

## **3.2 Green tea composition**

The chemical composition of green tea differs from climatic, seasonal, horticultural, and foliar synthesis [19]. The most important components of green tea are polyphenols. The catechins make up 80–90% of the flavonoids and about 40% of the water solids in green tea [20]. Green tea contains more catechins than other forms of tea. It is mainly due to post-harvest processing. The four main catechins contained in green tea are (−)-epicatechin (EC), (−)-epigallocatechin (ECG), (−)-epicatechin 3-gallate (ECG), and (−)-epigallocatechin gallate (EGCG) [21, 22] (**Figure 1**). EGCG, having the high concentration, has been widely studied for its health benefits. It contains (~60%), followed by EGC (~20%), ECG (~14%), and EC (~6%) (**Figure 2**). As mentioned above, the amount of catechins in any specific green tea beverage can vary greatly. At the same time, the standardized extract is available for use in addition [23].

## **3.3 Medicinal value of green tea**
