The nutritional significance of tea is confined to certain vitamins and minerals. Tea is able to contribute riboflavin, folic acid, /3-carotene, ct-tocopherol and phylloquinone, and is also one of the more significant sources of fluoride in the UK diet. The pharmacological action of caffeine in tea is so modified, probably by its interaction with polyphenols, that the beneficial properties of the alkaloid may be enjoyed without harmful side effects. Beneficial effects attributed to tea polyphenols acting synergistically with ascorbic acid include the strengthening of capillary blood vessels and an anti-atherosclerosis action. The potential value of tea has been well recognised in Russia but has received scant attention in the West.

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The deterioration of black tea, characterised by a loss of flavour and astringency and sometimes by the acquisition of undesirable ''taints" is accompanied by lipid hydrolysis and by autoxidative reactions that cause losses of theaflavins, amino acids, sugars, photosynthetic pigments and some volatile aliphatic constituents and increases in non-dialysable pigments and some volatile phenolic components. These reactions are accelerated by moisture and heat. Although lipid oxidation is insignificant except under hot dry conditions, it is postulated that oxidation of free fatty acids released during storage occurs during brewing, and has a profound influence on the quality of the liquor.

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