Alkaloids - Naturally occurring, nitrogen-containing compounds that are alkaline in solution. They usually have a bitter taste and are characterised by powerful physiological activity. Examples are nicotine and caffeine.

Antioxidant - A compound which retards oxidation.

Caffeine - An alkaloid found in tea and coffee which acts as a nerve stimulant and diuretic.

Catechins - A group of related polyphenolic compounds which occur in plants and are darkened by the action of certain plant enzymes and oxygen an example of browning of cut fruit and vegetables. Catechins can function as antioxidants.

Cardiovascular - concerning the heart and blood vessels.

Carcinogen - Any substance or agent that can produce a cancer.

Diuretic - An agent that promotes increased excretion of urine.

Electrophilic ultimate carcinogens - Substances which directly cause cancer by reacting with genetic material (DNA) and related cell components. (Many carcinogens, designated pro-carcinogens (q.v.), require conversion to the ultimate carcinogen by reactions taking place in the cells of the organism)

Epigallocatechin Gallate (EGCG, ECG, EGC, EC) - A family of substances related to the simple catechins which occur in green tea and which undergo browning reactions during processing to black tea.

Free radical - A highly reactive substance which, in some circumstances can lead to undesirable chemical changes in the body through oxidisation, e.g. hardening of the blood vessels and development of cancer.

Flavanols, flavonols, flavonol glycosides, flavandiols - Groups of related, naturally occurring chemicals in plants. A number of substances in these classes have antioxidant properties and many protect against deleterious changes brought about by free-radicals in the body.

Gallic acid - A plant polyphenolic which possess antioxidant properties.

Lipid - A member of the family of fats which occur in living tissues either structurally or for nutritional purposes.

Nicotinic acid - A water soluble vitamin B complex.

Oxygen - symbol O. A colourless, odourless gas constituting one-fifth of the atmosphere.

Oxidation - Changes which are brought about by oxygen.

Polyphenols - Compounds which contain several `phenol' groups and have antioxidant properties.

Polyphenolic components - Chemicals found in plants which have several groups containing an oxygen and a hydrogen atom (called a phenol group).

Procarcinogen - A substance capable of causing cancer but only when metabolised to a more reactive compound.

Riboflavin - Vitamin B2 Theaflavins - Yellow coloured polyphenols occurring in black tea.

Thearubigins - Red/brown pigments produced in black tea.