Potential effects of tea on health/medical benefits of tea/ importance of tea/ constituents/ chemical compound of tea /history of tea

Contents

1. History of Tea
2. health benefits of Tea
3. Constituents of Tea

• Protein
• Carbohydrates
• Lipids
• Vitamins
• Minerals
• Polyphenols
• Alkaloids

Tea plant

History of Tea

Tea has been the world’s most popular beverage, next to water. Emperor Shen Nang (2737 BC) is said to have used it as a beverage.

Tea is mentioned in Erh Ya, a Chinese dictionary 350 BC. The first monograph on tea was published by Lu Yu in 780 AD, who described the leaf and how and when it is plucked and explained how the leaf is manipulated in the hands, dried and sealed. The china tea plant was taken to Japan about 800 AD and regarded as a medicine for 500 years until green tea was developed and became a popular Japanese beverage.

In 1559 Europe was informed of tea by the Venetian writer, Gian Batista Ramusio. In England the first mention was by R L Wikham, in 1615.

Health benefits of Tea

Some of the health benefits are as follows;

1. Since caffeine relaxes the coronary vessels, it can be useful as a treatment for angina and myocardial infarction.
2. Useful in the treatment of bronchial asthma as the caffeine is a smooth muscle relaxant.
3. Tea can increase the gastric emptying therefore it is useful to relieve the post prandial distress.
4. There are evidences that tea is of value in gout.

Constituents of tea

The proportion in which the various constituents are present in the leaf will depend on the soil and climate and the stage of the leaf at harvest. The proportion of the constituents present in a cup of tea will be determined by the conditions under which the tea is brewed. Both brewing conditions and size of cup are subjected to considerable variation. In the discussion that follows on the composition of the extracted liquor, it is assumed that boiling water is added to black tea leaf in the ratio 100:1(weight for weight) and infused for 5 minutes, when about 35% of the solids are extracted. In estimating the daily intake of tea constituents, it is assumed that 5 to 6 cups (each of volume 170 ml) are consumed. Mai constituents are as follow;

1. Protein
2. Carbohydrates
3. Lipids
4. Vitamins
5. Minerals
6. Polyphenols
7. Alkaloids

Proteins and Tea

Although proteins constitute 5 to 23 % of black tea (dry weight), they make up less than 2% of the hot water-soluble solids, so that the daily intake is less than 70 mg. If milk is added, casein will complex with tea polyphenols, reducing the astringency but not interfering with the normal digestion of the protein.

Carbohydrates and Tea

Carbohydrates form only 4 to 5%of the solids in the liquor; hence it is considered as a low energy diet. Adding milk and sugar to the daily intake could give about I MJ (up to 10% of the daily energy intake).Ceylon tea has 1.4 to 5.7%ofsugars per dry weight of tea.

Lipids and Tea

Black tea has 2 to 3%of lipids, mainly phospholipids, glycolipids, sulpholipids, and triacylglycerols. The quantities extracted by water are negligible. The major fatty acids are linoleic and linolenic acids. These fatty acids are liberated in the free form during storage, when they become more easily extractable in hot water.

Vitamins and Tea

Each cup of tea provides 2.3 µg of thiamin, 21.5µg of riboflavin, and 127.5µg of niacin, 1.3µg folic acids, 21.4µg pantothenic acid, and 1.4µg biotin and 17µg inositol assuming 100% extraction into the liquor. Ascorbic acid in the fresh leaf is as high as in carrots but30 to 50% destroyed during manufacture and very little is extracted into the infusion.

Minerals and Tea

Most minerals are present in the leaf and many are extracted into the infusion. Its sodium content is low. The fluoride content varies widely, being 100 parts per million, between 40 and 80% of this being extracted in the water (about 0.1 mg per cup), giving less than 1 mg per day.

Polyphenols and Tea

Polyphenols constituent about 15 % (w/w) of black tea and the amount is varying according to the variety of tea, its geographical origin and environmental conditions.

Alkaloids and Tea

Tea also provides alkaloids. Black tea contains 1 to 5% caffeine, 0.05% theobromine and 0.0002% to 0.0004% theophylline. About 80% of the caffeine is extracted during brewing, giving a daily intake of about 0.3 g.