Collection of medicinal plants

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Collection of medicinal plants

• Drugs may be collected from wild or cultivated
  plants.
• 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.

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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.

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• 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.

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• 3- Stage of maturity and age
• The value and content of active constituents of
  many drugs depends on the stage of maturity and
  age.
• 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.

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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.

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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).

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• Fermentation
• Enzymatic transformation of the original plant
  constituents is sometimes desirable. e.g. Vanilla
  pods
• 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.

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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
  storage.
• 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
  aroma.
• Improper methods of storing and inadequate
  protection during storage can cause a pronounced
  deterioration.
• There are two principal reasons for
  deterioration
• Physiochemical moisture, heat, air and light.
• Biological fungi, bacteria, insects and rodents.

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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.

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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.

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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.

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• 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.

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• 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.

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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.

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• 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
  drugs.
• 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
  powders.

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• 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.

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Extracts

• Extracts can be defined as preparations of crude
  drugs which contain all the constituents which
  are soluble in the solvent used in making the
  extract.
• 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
  product.

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• 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.

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

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Choice of solvent

• The ideal solvent for a certain pharmacologically
  active constituent should
• Be highly selective for the compound to be
  extracted.
• Have a high capacity for extraction in terms of
  coefficient of saturation of the compound in the
  medium.
• 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.

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• 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.

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• 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.

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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