Tea.pptx

Black and green tea, its preparation, tea cultivation, preparation of black tea and green tea, chemical constituents (caffeine, catechin, tannins) and uses

1. Tea Camellia Thea Green tea Black tea Chai Patti Tea leaf

2. Biological source : It contains prepared leaves and leaf buds of Thea sinesis . Family Theaceae Geographical source : Native to India and Japan Available as black tea in India and Sri Lanka While as green tea in China and Japan Preparation : Black tea is obtained by fermenting fresh leaves and further drying with artificial heat. Green tea is obtained by putting tea leaves in copper pan and then drying by artificial heat.

3. Cultivation, collection and preparation : It is a small evergreen shrub reaches to height of 1.0 to 1.5 meters. Plant prefers adequate sunlight, well drained and loamy soil. It can grow in semi shade area. Requires pH range from 4.5 to 7.5 (can grow in acidic soil, but not in alkaline) Temperature range from 14 to 27 ˚C Seed can be sown as soon as it is ripe in a green house. Stored seed should be presoaked for 24 h in warm water. It usually germinates in one to three months. Prick out the seedlings into individual pots when they are large enough to handle and grow them on in light shade in the green house for at least their first winter. Plant them out into their permanent positions when they are more than 15 cm tall. Seedlings take 4–12 years before they start to produce seed.

4. Preparation of black tea : The leaves are first spread on trays and allowed to stand in the open area for about 18 to 24 hrs. They are next rolled , usually between two flat surfaces , a process which breaks the cellular structures of the leaf and liberates cell contents. After rolling the leaves are fermented by laying them on glass or other non-porous material and maintaining a temperature of 20 to 27˚C in carefully adjusted humid atmosphere. The type of fermentation is  enzymatic oxidation , which occurs when the cell walls of the tea leaves break down and the interior components of the cells are exposed to the air. Exposure to oxygen leads to a chemical reaction with organic enzymes inside the leaves.

5. The color of the leaves changes from green to yellow to coppery red. These changes are due to an oxidase enzymes named thease which converts the tannin into a insoluble reddish brown phlobaphene and the chlorophyll also undergoes changes. The next process is drying at temp of about 65 ˚C for which purpose the fermented leaves placed on trays are placed on a heated chamber until the moisture present is about 3%. The tea is finally shifted, graded and packed.

6. Preparation of green tea : It is prepared by exposing the freshly collected leaves to the air until moisture is removed. Then they are roasted and stirred continuously until leaves become moist and flaccid. Then they are passed to rolling table and subjected to a pressure which removes moisture. Then the leaves are shaken out on copper pans and roasted again till leaves are dull green in colour. The tannin is not oxidized and the leaves retain their green color more or less. Then leaves are winnowed, screened, graded into various varieties.

7. Morphology : Leaves : Dark green in colour Lanceolate or elliptical Base tapering Margin serrate Acuminate apex Young leaves are hairy While matured are glabrous Flowers : Solitary White colour Odour : Characteristic Taste : bitter

8. Microscopy : The trichomes are thick walled, unicellular, covering which arise on the lower surface and large number in young leaves. palisade as discontinuous over the midrib. Cluster crystals of calcium oxalate are scattered in phloem and in parenchyma. The mesophyll region consists of two rows of palisade parenchyma cells and are large lignified sclerieds .

9. Chemical constituents : Tea is particularly rich in 3 flavonoid classes: F lavan-3-ols (or catechins), O ligomeric flavonoids (including thearubigins and theaflavins generated during fermentation) F lavonols (e.g., quercetin) The leaves are rich source of Caffeine - purine alkaloids (1-5%). It also contains theobromine and theophylline in minor quantity. The color of tea leaves is due to tannin (10 to 20% G allotannic acid). The agreeable odour is due to presence of a yellow Volatile oil. Tea leaves also contain an enzymatic mixture called Thease.

10. Catechin Quercetin Caffeine

11. Chemical tests : Caffeine and other purine alkaloids, gives murexide colour reaction. Caffeine is taken in a Petri dish to which hydrochloric acid and potassium chlorate are added and heated to dryness. A purple colour is obtained by exposing the residue to vapors of dilute ammonia. In addition of alkali the purple colour disappears. Caffeine also produces white precipitate with tannic acid solution. Uses : CNS Stimulant Astringent diuretic It is given along with ergotamine tartarate as a specific analgesic in migraine.

12. Adulterants: Tea has been adulterated with foreign leaves as well as with exhausted tea leaves that have been rolled and dried. Other drugs described as Tea: Bush tea: Cyclopia Marsh tea: Ledum palustre (Chinese plant) Kaporie tea: Epilobium angustifolium (European countries) Mexican tea: Chenopodium amboriodes (Mexican) Kutai tea: Vascinium mytillus (Bilberry) None of these contain caffeine