A tea leaf from the Camellia sinensis shrub contains a wide range of difference substance, including carbohydrates, amino acids, lipids, minerals and vitamins. The major ingredient in tea is a class of polyphenols known as catechins.
Examples of vitamins found in the tea leaf are vitamin C, vitamin B6, thiamine and riboflavin. Commonly found minerals include fluorine, potassium and calcium.
One of the most interesting amino acids found in tea is called theanine and is believed to make us relaxed, prevent anxiety and produce a more restful sleep. As the tea plant grows, theanine is converted into catechins, and the theanine-catechin ratio is therefore continuously changing in a growing tea leaf.
A tea leaf harvested during the beginning of the growing season can therefore have a higher theanine content compared to a leaf from the same bush harvested late that year.
In tea, you will also find higher or lower amounts of caffeine; a xanthine alkaloid capable of stimulating the central nervous system.
The exact amounts of caffeine will vary a lot from tea to tea since the tea content is greatly affected by how the tea leaves are treated once they have been picked from the tea shrub. A long preparation process where the leaves are allowed to oxidize will typically lead to a high caffeine content, and this is why black tea and oolong tea usually contain a much higher amount of caffeine compared to green tea and white tea.
True tea is always made from the Camellia sinensis shrub, but in everyday language we refer to a wide range of different hot and cold brews as tea. Herbal teas can be made from many other plants than Camellia sinensis and will therefore contain other chemicals. Examples of popular infusions made from other species than Camellia sinensis are Anise tea, Chamomille tea and Lemon grass tea.