The composition of green tea varies according to the growing and harvesting methods, but the most abundant components are polyphenols, which are predominantly flavonoids (e.g. catechin, epicatechin, epicatechin gallate, epigallocatechin gallate, proanthocyanidins). Caffeine content in green tea varies but is estimated at about 3%, along with very small amounts of the other common methylxanthines, theobromine and theophylline (Graham 1992). It also contains many other constituents, such as tannin, diphenylamine, oxalic acid, trace elements and vitamins.
Epigallocatechin gallate is one of the most abundant polyphenols in tea and is regarded as the most significant pharmacologically active component.
Clinical note — The difference between teas
Black, green and oolong tea are produced from the same plant (Camellia sinensis) but differ in polyphenol content according to the way the leaves are processed. Blacktea is made from oxidised leaves whereas oolong tea is made from partially
oxidised leaves and green tea leaves are not oxidised at all. Because the oxidising process converts many polyphenols compounds into others with less activity, green tea is considered to have the strongest therapeutic effects and the highest polyphenol content (Lin et al 2003). Caffeine concentrations also vary between the different teas: black tea > oolong tea > green tea > fresh tea leaf (Lin et al 2003). Variation in caffeine content is further influenced by growing conditions, manufacturing processes and size of the tea leaves (Astill et al 2001). The highest quality leaves are the first spring leaf buds, called the 'first flush'. The next set of leaf buds produced is called the 'second flush' and considered to be of poorer quality. Tea varieties also reflect the area they are grown in (e.g. Darjeeling in India), the form produced (e.g. pekoe is cut, gunpowder is rolled) and processing method (black, oolong or green) (Ulbricht & Basch 2005)._
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