Tea

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Chapter: Pharmacognosy and Phytochemistry : Drugs Containing Alkaloids

It contains the prepared leaves and leaf buds of Thea sinensis (Linne) kuntz., belonging to family Theaceae.


TEA

Biological Source

 

It contains the prepared leaves and leaf buds of Thea sinensis (Linne) kuntz., belonging to family Theaceae.

 

Geographical Source

 

It is mainly cultivated in India (Assam), Ceylon, Japan and Java.

 

Cultivation and Collection

 

It is an evergreen shrub growing to 4 m by 2.5 m at a slow rate. The plant prefers light (sandy) and medium (loamy) soils and requires well-drained soil. The plant prefers acid and neutral soils and can grow in very acid soil. It can grow in semishade (light woodland). It requires moist soil and prefers a pH between 5 and 7. Prefers the partial shade of light woodland or a woodland clearing. It is reported to tolerate an annual rainfall of 70–310 cm, an average annual temperature range of 14–27°C and a pH in the range of 4.5–7.3. It prefers a wet summer and a cool but not very frosty dry winter. 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 and the hard covering around the micropyle should be filed down to leave a thin covering. 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 and give them some protection from winter cold for their first year or three outdoors. Seedlings take 4–12 years before they start to produce seed.

 

Characteristics



                                         Twig of tea plant 


Leaves are dark green in colour, lanceolate or elliptical, on short stalks, blunt at apex, base tapering, margins shortly serrate, young leaves hairy, older leaves glabrous.

 

Microscopy

 

The epidermal cells are made of polygonal cells which are slightly wavy walls. It consist on itself stomata and trichomes. The trichomes are thick walled, uni-cellular, conical (covering) which arise on the lower surface and in large number in young leaves. The mesophyll region consist of two rows of palisade parenchyma cells and large lignified sclereids which arise at some intervals and are extended across the mesophyll from one epidermis to the other. Cluster crystals of calcium oxalate are scattered in phloem and in parenchyma. In the midrib area a prominent ridge is present both above and below. Vascular bundle consisting of xylem and phloem are present; the entire region being covered by slightly lignified band of pericyclic fibres. The pericyclic fibres are up to four fibres in width at the widest region. The remaining portion is covered with spongy parenchyma with scattered lignified sclereids.

 

Chemical Constituents

 

The leaves are a rich source of caffeine (1–5%). It also contains theobromine and theophylline in minor quantities. The colour of tea leaves is due to tannin (10–20% gallotannic acid). The agreeable odour is due to presence of a yellow volatile oil. Tea leaves also contain protein, wax, resin and ash.

 


 

Chemical Tests


1. Caffeine and other purine alkaloids, gives murexide colour reaction. Caffeine is taken in a petridish to which hydrochloric acid and potassium chlorate are added and heated to dryness. A purple colour is obtained by exposing the residue to vapours of dilute ammonia. In addition of fixed alkali the purple colour disappears.

 

2. Caffeine also produces white precipitate with tannic acid solution.

 

Uses

 

It is used as stimulant, astringent and also as diuretic.

 

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