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Collection of medicinal plants


... storage of crude drugs are objectionable, e.g. drugs containing volatile oils ... brittle by bacterial attack which makes the cotton wool objectionable and dusty. ... – PowerPoint PPT presentation

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Title: Collection of medicinal plants

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Collection of medicinal plants
  • Drugs may be collected from wild or cultivated
  • It is known that the active constituents of
    medicinal plants are affected by many factors and
    may vary during the course of plant growth.
  • Proper time of collection is very important to
    obtain a drug of a good quality.

Factors affecting collection
  • Time of the year
  • The plant may contain a substance in winter that
    is not present in summer, or its amount varies
    markedly e.g. Rhubarb contains no anthraquinone
    in winter, instead it contains anthranols, which
    in summer, are oxidized to anthraquinones.
  • Colchicum corm is free from bitterness and is
    devoid of the alkaloid colchicine in autumn,
    hence is used in Austria as a food, instead of
    potatoes. Bitterness starts to appear in spring
    and early summer when it is used as a drug.

  • 2- Time of the day
  • Some drugs, like Digitalis, contain different
    amounts of active constituents in different times
    of the day. Being highest in the afternoon.

  • 3- Stage of maturity and age
  • The value and content of active constituents of
    many drugs depends on the stage of maturity and
  • Conium fruits contain coniin when fruits are
    mature and unripe.
  • Santonica flowers are rich in santonin, when
    unexpanded, when it starts to open, the santonin
    content decreases.

Drying of crude drugs
  • Reasons for drying
  • To help in their preservation.
  • To fix their constituents, by preventing
    reactions that may occur in presence of water.
  • To prevent the growth of micro-organisms such as
    bacteria and fungi.
  • To facilitate their grinding.
  • To reduce their size and weight.
  • Insufficient drying favors spoilage by
    micro-organisms and makes it possible for
    enzymatic destruction.

Methods of drying
  • Drying is carried out either by natural or
    artificial methods.
  • 1- Natural drying this is accomplished by
    natural air in sun or shade.
  • 2- Artificial drying this is a rapid method done
    at well-controlled temperature and is
    accomplished by
  • direct fire.
  • Use of heated stones.
  • Use of stoves.

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  • Lyophilization (Freeze drying)
  • Frozen material is placed in an evacuated
    apparatus which has a cold surface maintained at
    -60 to -80 C. Water vapour from the frozen
    material passes rapidly to the cold surface.
  • It is used for drying heat-sensitive substances
    e.g. antibiotics and proteins.
  • Chemical drying using desiccators
  • An absolutely dried drug is that completely freed
    from water, when exposed to air it absorbs 8-10
    of moisture and is called air-dry drug.

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  • Stabilization
  • On long storage, enzymatic reactions will slowly
    destroy the constituents, because the last traces
    of water can never be removed.
  • In order to avoid this degradation, the enzymes
    should be destroyed before drying, a process
    usually called stabilization.
  • The most common method being brief exposure (a
    few minutes only) of the plant material to
    ethanol vapor under pressure (0.5 atm).

  • Fermentation
  • Enzymatic transformation of the original plant
    constituents is sometimes desirable. e.g. Vanilla
  • The fresh material is placed in thick layers,
    sometimes covered and often exposed to raised
    temperatures (30-40 C) and humidity, so as to
    accelerate the enzymatic processes.
  • The fermented product must be dried afterwards to
    prevent attack by microorganisms, e.g. moulds.

Preservation and protection of crude drugs
  • Storage represents the last stage of preparing
    crude drugs. drugs usually deteriorate along the
    time of storage,
  • except in few cases e.g. Cascara and Frangula
    should not be used except after certain period of
  • Certain drugs as Nux vomica are hardly affected
    by storage.
  • Generally, changes that take place during storage
    of crude drugs are objectionable, e.g. drugs
    containing volatile oils gradually lose their
  • Improper methods of storing and inadequate
    protection during storage can cause a pronounced
  • There are two principal reasons for
  • Physiochemical moisture, heat, air and light.
  • Biological fungi, bacteria, insects and rodents.

Physicochemical factors
  • Moisture moisture sometimes affects drugs
    adversely through activating the enzymes (as in
    cardiac glycosides).
  • Heat rise of temperature up to 45 activates the
    enzymes causing decomposition of active
    constituents. Volatile oil containing drugs are
    also affected by higher temperatures, their
    content decreases.
  • Air oxygen of air oxidizes certain constituents
    of crude drugs, e.g. linseed and lemon oil, it
    causes rancidity of fixed oils and resinification
    of volatile oils.
  • Light it affects drugs, especially those having
    marked colours.e.g. yellow colour of Rhubarb
    changes to reddish tint, white coloured corollas
    turn brown.

Biological factors
  • Bacteria cotton fibres are rendered brittle by
    bacterial attack which makes the cotton wool
    objectionable and dusty.
  • Moulds the mycelium of delicate hyphae produces
    an unpleasant mass of clinging particles in
    powdered drugs.
  • Insects they seem to attack all drugs but have
    preferences to certain drugs as ginger,
    belladonna, kola, liquorice,.....
  • Insects which infest vegetable drugs include
    beetles, mites and moths. They render drugs
    porous and powdery.

Methods for controlling insects
  • Heat treatment it is the simplest method and is
    done by exposing the drug to a temperature of
    60-65. it is effective especially for insect eggs
    which are not affected by insecticides.
  • Fumigation this is done by volatile insecticidal
    agents in closed areas e.g. CCL4, CS2, CN. Most
    fumigants do not kill eggs of insects. It is
    advisable to repeat fumigation at intervals to
    obtain better results.

  • 3. Liming liming of certain drugs as ginger,
    nutmeg to protect against insect attack provides
    only partial protection.
  • 4. Low temperature storage this method is
    preferred to fumigants and liming. Adult insects,
    pupae, larvae and eggs are sometimes killed by
    very low temperatures.
  • 5. Exposure to alternate periods of low and high
    temperatures frequently is more effective for
    killing insects than a prolonged period of low
    temperature exposure.

  • Rodents they cause much spoilage of crude
    drugs during storage, especially if wrapped in
    paper, cloth or put in cardboard or wooden
    containers. The presence of rodent's filth,
    excreta, hairs causes rejection of the drug.

Grinding of crude drugs
  • Regardless of whether the crude drug is to be
    used for isolation of a pure compound or for
    manufacture of a simple preparation, the first
    operation that must be performed is grinding of
    the plant material to a powder of suitable
    particle size.
  • It is important that the particles are of as
    uniform size as possible.
  • Excessive dust can clog percolators and result in
    a turbid extract which is hard to clarify.

  • Large particles take a longer time for complete
    extraction than small ones.
  • Large differences in particle size thus slow down
    the extraction process.
  • Types of machines used for grinding crude drugs
  • Hammer mill a common type for grinding crude
  • Knife mill is useful for production of low-dust
    powders of leaves, barks and roots for subsequent
    percolation or maceration.
  • Tooth mill is used for production of very fine

  • Notes
  • Grinding produces a certain amount of heat which
    must be observed when grinding crude drugs
    containing heat-sensitive compounds.
  • Mills cooled with liquid nitrogen are available
    for such purposes.
  • Cold grinding is also preferable for crude drugs
    containing volatile oils.
  • Following grinding, the material must be sifted
    to ensure the proper particle size.

  • Extracts can be defined as preparations of crude
    drugs which contain all the constituents which
    are soluble in the solvent used in making the
  • In dry extracts all solvent has been removed.
  • Soft extracts and fluid extracts are prepared
    with mixtures of water and ethanol as solvent.
  • Tinctures are prepared by extraction of the crude
    drug with five to ten parts of ethanol of varying
    concentration, without concentration of the final

  • Plant constituents are usually contained inside
    the cells. Therefore, The solvent used for
    extraction must diffuse into the cell to dissolve
    the desired compounds whereupon the solution must
    pass the cell wall in the opposite direction and
    mix with the surrounding liquid.
  • An equilibrium is established between the solute
    inside the cells and the solvent surrounding the
    fragmented plant tissues.

  • The speed with which this equilibrium is
    established depends on
  • Temperature
  • pH
  • Particle size
  • The movement of the solvent

Choice of solvent
  • The ideal solvent for a certain pharmacologically
    active constituent should
  • Be highly selective for the compound to be
  • Have a high capacity for extraction in terms of
    coefficient of saturation of the compound in the
  • Not react with the extracted compound or with
    other compounds in the plant material.
  • Have a low price.
  • Be harmless to man and to the environment.
  • Be completely volatile.

  • Aliphatic alcohols with up to three carbon atoms,
    or mixtures of the alcohols with water, are the
    solvents with the greatest extractive power for
    almost all natural substances of low molecular
    weight like alkaloids, saponins and flavonoids.
  • According to the pharmacopoeias, ethyl alcohol is
    the solvent of choice for obtaining classic
    extracts such as tinctures and fluid, soft and
    dry extracts.

  • The ethanol is usually mixed with water
  • 1- to induce swelling of the plant particles
  • 2- to increase the porosity of the cell walls
    which facilitates the diffusion of extracted
    substances from inside the cells to the
    surrounding solvent.
  • For extraction of barks, roots, woody parts and
    seeds the ideal alcohol/water ratio is about 73
    or 82.
  • For leaves or aerial green parts the ratio 11
    is usually preferred in order to avoid extraction
    of chlorophyll.

Extraction Procedures
  • There are many procedures for obtaining extracts
  • 1- Infusion 2- Maceration
  • 3- Percolation 4- Digestion
  • 5- Decoction 6- Continuous hot extraction
  • 7- Solvent-solvent precipitation
  • 8- Liquid-liquid extraction
  • 9- Distillation 10- Specific procedures
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