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Collection of medicinal plants

Drugs may be collected from wild orcultivated plants.

It is known that the active constituents ofmedicinal plants are affected by manyfactors and may vary during the course ofplant growth.

Proper time of collection is very important toobtain a drug of a good quality.

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Factors affecting collection

1. Time of the year:The plant may contain a substance in winter that is notpresent in summer, or its amount varies markedly e.g.Rhubarbcontains no anthraquinone in winter, insteadit contains anthranols, which in summer, are oxidized to

anthraquinones.

Colchicum cormis free from bitterness and is devoid ofthe alkaloid colchicine in autumn, hence is used in

Austria as a food, instead of potatoes. Bitterness startsto appear in spring and early summer when it is usedas 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 theafternoon.

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3- Stage of maturity and age:

The value and content of activeconstituents of many drugs depends onthe stage of maturity and age.

Conium fruits contain coniin when fruitsare 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:1. To help in their preservation.

2. To fix their constituents, by preventingreactions that may occur in presence of water.

3. To prevent the growth of micro-organisms suchas bacteria and fungi.

4. To facilitate their grinding.

5. To reduce their size and weight.6. Insufficient drying favors spoilage by micro-

organisms and makes it possible for enzymaticdestruction.

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Methods of drying

Drying is carried out either by natural or artificialmethods.

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 accomplishedby:

direct fire.

Use of heated stones.

Use of stoves.

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http://www.pemed.com/lab/incubat/bmstabiltherm02_6.jpghttp://www.pemed.com/lab/incubat/bmstabiltherm01_5.jpg

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Lyophilization (Freeze drying):

Frozen material is placed in an evacuated apparatus which has a

cold surface maintained at -60 to -80C. 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 calledair-dry drug.

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http://www.2spi.com/catalog/supp/images/TechniDomeDesiccator.jpg

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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 plantconstituents 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. drugsusually deteriorate along the time of storage,

except in few cases e.g. Cascara and Frangula should not be usedexcept after certain period of storage.

Certain drugs as Nux vomica are hardly affected by storage.

Generally, changes that take place during storage of crude drugsare objectionable, e.g. drugs containing volatile oils gradually losetheir 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 factors1. Moisture: moisture sometimes affects drugs adversely

through activating the enzymes (as in cardiacglycosides).

2. Heat: rise of temperature up to 45 activates theenzymes causing decomposition of active constituents.Volatile oil containing drugs are also affected by highertemperatures, their content decreases.

3. Air: oxygen of air oxidizes certain constituents of crudedrugs, e.g. linseed and lemon oil, it causes rancidity offixed oils and resinification of volatile oils.

4. Light: it affects drugs, especially those having markedcolours.e.g. yellow colour of Rhubarb changes toreddish tint, white coloured corollas turn brown.

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Biological factors

1. Bacteria: cotton fibres are rendered brittle by bacterialattack which makes the cotton wool objectionable anddusty.

2. Moulds: the mycelium of delicate hyphae produces anunpleasant mass of clinging particles in powdereddrugs.

3. Insects: they seem to attack all drugs but havepreferences to certain drugs as ginger, belladonna, kola,liquorice,.....

Insects which infest vegetable drugs include beetles, mitesand moths. They render drugs porous and powdery.

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Methods for controlling insects

1. Heat treatment: it is the simplest method andis done by exposing the drug to a temperatureof 60-65. it is effective especially for insecteggs which are not affected by insecticides.

2. Fumigation: this is done by volatileinsecticidal agents in closed areas e.g. CCL4,

CS2, CN. Most fumigants do not kill eggs ofinsects. It is advisable to repeat fumigation atintervals to obtain better results.

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3. Liming: liming of certain drugs as ginger,nutmeg to protect against insect attack providesonly partial protection.

4. Low temperature storage: this method ispreferred to fumigants and liming. Adult insects,

pupae, larvae and eggs are sometimes killed byvery low temperatures.

5. Exposure to alternate periods of low and

high temperatures: frequently is more effectivefor killing insects than a prolonged period of lowtemperature exposure.

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Rodents: they cause much spoilage ofcrude drugs during storage, especially if

wrapped in paper, cloth or put in

cardboard or wooden containers. Thepresence 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 aturbid 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 theextraction process.

Types of machines used for grinding crude drugs:

1. Hammer mill; a common type for grinding crudedrugs.

2. Knife mill; is useful for production of low-dustpowders of leaves, barks and roots for subsequent

percolation or maceration.3. Tooth mill; is used for production of very fine

powders.

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Notes:

Grinding produces a certain amount of heatwhich must be observed when grinding crude

drugs containing heat-sensitive compounds.

Mills cooled with liquid nitrogen are availablefor 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 crudedrugs which contain all the constituents which are

soluble in the solvent used in making the extract.

In dryextracts all solvent has been removed.

Softextracts and fluidextracts are prepared withmixtures of water and ethanol as solvent.

Tincturesare prepared by extraction of the crudedrug 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:

1. Temperature

2. pH

3. Particle size

4. The movement of the solvent

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Choice of solvent

The ideal solvent for a certain pharmacologically

active constituent should:

1. Be highly selective for the compound to be extracted.

2. Have a high capacity for extraction in terms of

coefficient of saturation of the compound in the

medium.

3. Not react with the extracted compound or with other

compounds in the plant material.

4. Have a low price.

5. Be harmless to man and to the environment.

6. 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 alcoholisthe 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 ofbarks, roots, woody partsand seedsthe

ideal alcohol/water ratio is about 7:3 or 8:2.

Forleaves or aerial green partsthe ratio 1:1 is usually

preferred in order to avoid extraction of chlorophyll.

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Extraction ProceduresThere are many procedures for obtaining

extracts1- 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