Tea: Types and Active Constituents

Tea

• Tea originates from the prepared leaves and leaf bud of Thea sinensis L. (Camellia thea Link.), belonging to the family Theaceae.
• The part used consists of the two adjacent young leaves together with the stem + bud.
• It is geographically found in India, Serilanka, China, and Japan.

Types of Tea

• Green tea is made through rapid drying at high temperatures, stopping or destroying the oxidase enzyme, preventing fermentation, and thus no oxidation of tannins occurs, retaining the chlorophyll color.
• Black tea is made through slow drying at no high temperature, allowing complete oxidation by oxidase enzyme, complete fermentation, oxidation of tannins, and a change in chlorophyll to a dark color.

Active Constituents

• Active constituents are present in both types of tea
• Green tea:
  • Contains soluble caffeine-phlobatannins complex due to the destruction of oxidase enzyme by high temperature, preventing fermentation.
  • Tannins are in the form of a complex with caffeine and are soluble.
  • Contains less free caffeine but more tannins.
  • Flavonoids glycosides: Green tea is used as antioxidant and antitumor as it have more Flavonoids
• Black tea:
  • Contains soluble caffeine-phlobatannins.
  • Insoluble phlobaphenes (Tannins) + free caffeine due to complete hydrolysis of complex by oxidase enzyme during fermentation.
  • Tannins are in the form of phlobaphenes after hydrolysis and are insoluble.
  • More caffeine due to complete hydrolysis of complex but less Tanning.
• Both contain traces of theobromine & theophylline alkaloids, volatile oil, and saponin glycosides.

Digitalis (Foxglove)

• Digitalis (Digitalis purpurea and Digitalis lanata) belongs to the family Scrophulariaceae. It is considered simple
• The part used: dried leaves
• It has active constituents including Digoxin, Digitoxin, Lanatoside A & Lanatoside C and Saponin glycosides.

Confirmatory Chemical Tests for Digitalis

• Baljet test: For cardiac glycosides, an alcoholic extract gives with Baljet reagent (Picric acid +10% NaOH = Sodium picrate) will result in an orange yellow color compared with a blank.
• Keller – Killiani test: For deoxy sugar in glycone part, an acetic acid extract gives with FeCl + Conc H₂SO₄ which will result in a reddish-brown ring at the junction of the two layers, and the upper layer turns bluish green.
• Froth test: For saponin glycosides, a powdered drug is shaken with water to give a persistent froth that remains for 5 minutes.

Medicinal Uses for Digitalis

• Due to the presence of cardiac glycosides, Digitalis has a cardiotonic action on a diseased heart.
  • It strengthens the heartbeat.
  • It increases the force of contraction of the heartbeat.
  • It enables the heart to beat more strongly, slowly, and regularly without requiring more oxygen.

Senna (Alexandrian & Indian Senna)

• Senna (Cassia acutifolia (Alexandrian Senna) and Cassia angustifolia (Indian Senna)) compound belonging to the family Leguminosae.
• Active constituents include anthraquinones glycosides (Sennoside A, B, C, D upon hydrolysis yields Sennidin A, B, C, D) and mucilage (carbohydrates).

Confirmatory Chemical Tests for Senna

• Borntrager's test: For free anthraquinones, a chloroformic extract gives with NH4OH a rose (pink) to intense red in the aqueous layer.
• Modified borntrager's: For combined anthraquinones, a chloroformic extract gives with NH4OH a rose (pink) to intense red in the aqueous layer.

Medicinal Uses for Senna

• Due to the presence of anthraquinones glycosides, Senna is used as a laxative and powerful cathartic in the treatment of constipation.

Precautions for Senna

• Due to the presence of anthraquinones glycosides, Senna should not be taken for more than 10 days since it leads to weakening of the large bowel muscles.

Confirmatory Chemical Tests

• Murexide test: for Caffeine.
  • Aqueous decoction, evaporate, residue gives with Conc. HCl + H₂O, then evaporate till dryness, yellow color is formed which turns crimson red residue + vapors of ammonia, a violet color is formed.
• Ferric chloride test: for tannins: Aqueous extract gives with FeCl3 green color.
• KOH test: for flavonoids glycosides: Acidic extract gives with KOH yellow color.
• Froth test: for Saponin glycosides: Powdered drug is shaken with water to give persistent froth that remains for 5 minutes.

Medicinal Uses of Tea

• Due to presence of caffeine tea acts as: CNS stimulant, Diuretic, and weak smooth muscle relaxant.
• Due to presence of tannins: Tea is used as antidiarrheal drug (Constipating agent).
• Green tea is antioxidant & anticancer.

Precautions of taking large doses of tea

• Taking large doses of tea causes: Gastritis and Nervous irritability.
• Taking large doses of tea causes: Anemia, Constipation, a habituation syndrome and an increase in heart rate.

Precautions

• The cardiac glycosides of Digitalis are excreted very slowly with a cumulative effect (may be fatal) so this is preferred as long-term medication.

Morphology

• The petiole is petiolate.
• The lamina (leaf blade):
  • Apex is acute.
  • Shape is lanceolate and decurrent.
  • Margin is entire but ciliated at the base.
  • Form (Type) is simple.
  • Venation is reticulate anastomosing near the margin.
  • Apex is exstipulate symmetric, decurrent (When the base continues downwards as wings along the petiole).
• Phyllotaxis is alternate.

Key Elements

• Fragments of epidermal cells with beaded anticlinal walls and anomocytic stomata with striated cuticle characteristic of Digitalis.
• Three types of glandular hairs including: bicellular biserriate head unicellular stalk, Unicellular head, unicellular stalk (Capitate hair), Unicellular head, multicellular uniserriate stalk.
• Two types of non-glandular hairs including: Collapsed hair (Characteristic of Digitalis) and Multicellular uniserriate.
• It doesn't contain any type of calcium oxalate.

Netted venation

• A characteristic feature of dicotyledons
  • Pinnately netted: Veins branch off or radiate from a central mid vein.
  • Palmately netted: Several major veins radiate out from a point.

Leaf Arrangement on the stem (Phyllotaxis)

• Alternate: Leaves may occur in an alternate arrangement (1 leaf per node).
• Opposite: Nodes are opposite each other on the stem (2 leaves per node).
• Opposite Decussate: This is a special case of opposite, where each successive pair of leaves is at a right angle to the previous pair (typical for the mint family).
• Whorled: Three or more leaves arise from one node.

Forms of leaves

• Simple: Leaves have blades that are not divided into distinct morphologically separate leaflets, but form a
  • Entire (single) blade: the leaf is not divided.
  • Lobed or deeply lobed
    • Pinnately lobed: lobes are arranged on the sides of a central axis, like a feather.
    • Palmately lobed: lobes spreading radially from a point, like a finger on a hand.
• Compound: Each blade is divided into smaller leaflets to form either
  • Pinnate: leaflets arise along sides of the rachis which is the extension of the petiole.
    • Paripinnate: The leaflets are in even number.
    • Imparipinnate: The leaflets are in odd number.
  • Palmate: the leaf is divided into 5 or more leaflets radiating from the top of the petiole.

Venation

• Parallel venation is a characteristic feature of monocotyledons.
• Veins run approximately parallel to each other.
• It is divided in to:
  • In multicostate venation, there are multiple main veins or ribs that radiate from the base of the leaf.
  • In unicostate venation, a single main vein runs through the center of the leaf blade.

Morphological Structure of a Dicot Leaf

• Leaves display distinct variations in shape and form, making them useful for identification.
• Leaves consists of a broad, flat lamina/blade and stalk like petiole, some leaves possess small/leaf like outgrowth from the base called stipules.
• Petiole (optional): It attaches blade to stem.
• Lamina/Blade: Broad, flat in shape. It collects light for photosynthesis.
• Veins: It contains vascular tissue.
• Axil: It is the point of attachment of the leaf at the node of the stem. It is the intersection of petiole and stem and sometimes has axillary bud.
• Stipules (optional): Outgrowths at base of the leaf.

Introduction to Leaves

• The leaf is a lateral outgrowth (appendage), of limited growth, on the stem from which it differs in structure and organization.
• It is usually flattened, having in its axil (in the angle between it and the stem) bud or branch.
• It has neither nodes nor internodes and consists mainly of primary tissues.
• The leaves' function is the assimilation of glucose and its derivative (starch) from water and carbon dioxide (photosynthesis) using energy provided by sunlight.
• Different kinds of leaves:
  • Cotyledons (seed leaves): The leaves of the embryo, serving for storing of food.
  • Foliage leaves: The ordinary green leaves. (photosynthesis)
  • Floral leaves: The reproductive parts of the flower which include sepals, petals, stamens, and carpels.
  • Bract leaves: Leaves having a flower in their axils.
  • Scale leaves: Which occur on subterranean stems (thin, membranous and devoid of chlorophyll).
  • Modified leaves: When the leaf is modified into special structure for the purpose of carrying out special function.

Key Elements (Senna)

• Palisade cells (leaf organ).

Side effects (Senna)

• Due to presence of anthraquinones glycosides:
• It has a slightly bitter taste and causing nausea and as being a cathartic (very strong laxative) It causes gripping and colic so it is mixed with other aromatic, carminative herbs that relax the intestinal muscles examples: Mentha, anise, cardamom, clove, antispasmodic (belladonna).

Contraindications (Senna)

• It should not be taken during pregnancy, since it causes muscle contraction which may lead to abortion, and this is due to presence of anthraquinones glycosides and woman breastfeeding

Morphology (Senna)

• The Petiole of the senna is petiolate.
• The lamina (leaf blade):
  • Shape is obovate, lanceolate.
  • Margin is entire.
  • Form (Type) is compound, pinnate, paripinnate (even number).
  • Venation is reticulate (netted) and pinnately reticulate.
• Phyllotaxis is alternate.

Histology of Leaves

• The ordinary leaf consists of:
  • Upper and lower epidermis: covered with stomata which are responsible for the gaseous exchange.
  • Mesophyll: lies in between the two epidermis.
  • Cortical tissues: surrounds the vascular bundle that traverse the mesophyll.
  • Vascular system.

Microscopic characteristics of leaves

• Form and number of stomata.
• Trichomes: including Secretory (glandular hairs) and covering trichomes (non-glandular hairs)
• Presence of crystals such as calcium oxalate.

Epidermal cells

• Upper and lower epidermal cells with paracytic stomata (leaf organ).
• Warty hair, non glandular, unicellular thick wall, curved and covered with warty cuticle (Characteristic of Senna).
• Cicatrix hair.
• Crystal sheath with prisms of Ca-Oxalate. (Characteristic of Senna)
• Clusters of calcium oxalate.