Crude plant drugs are obtained from the various organs of both wild and cultivated plants. The quality and quantity of the active constituents of these plants vary greatly with the time of the year, the active constituents of these plants vary greatly with the time of the year, the age of the plant and the method of procuring them. Thus the therapeutic value and also the keeping quality of these drugs are largely dependent on the time of their collection and the method employed in their collection. Untimely collection and the use of improper methods may result in the production of substandard or even useless drugs. Certain rules and methods should therefore be followed in procuring crude drugs from their natural sources. Some of the general methods and rules of collection of crude drugs from plants are described and discussed below.
In simple terms, collection involves the act of procuring a crude drug from its natural habitat or natural source. Crude drugs are produced in almost all countries of the world. Their habitats and sources thus vary greatly depending on the climatic condition of the country and the type of the drug collected. Crude drugs may be collected from both wild and cultivated sources using either casual, unskilled labourer or skilled, educated workers and scientists depending on the type and source of the educated workers and scientists depending on the type and source of the drug. Many drugs of commercial importance such as Senna, Tragacanth, Podophyllum are still collected from wild sources, most often by the unskilled local collectors. But this practice of collecting drugs from wild sources by unskilled people should be discouraged, because carelessness or ignorance on the part of the collector may result in complete or partial substitution and admixture. This is more likely when the drug plants grow mixed with other similar looking plants or is very difficult to collect or the natural source is very scarce. Collection from cultivated sources by skilled collectors is the most ideal practice, which ensures a true natural source and a reliable product. Most of the important drugs like Opium, Cinchona, Cinnamon, Cascara, Rhubarb and Pyrethrum are now cultivated all over the world.
Methods of collection:
The method of collection either from wild or cultivated source depends on the type of the drug and also on the pharmaceutical requirement of the drug. Drugs may be collected by hand labour or by mechanical means. Hand picking is used when a drug is collected from a mixed vegetation and where skilled selection of plant parts, as in Tea, is an important factor. Mechanical devices like mowers, binders, pickers and combined arc employed for collecting or harvesting drugs in large quantities from cultivated single crop fields. Mechanical means are particularly used where speed and reduced cost of production are required. Different types of device are used for collecting various plant organs. For example, fruits and seeds are cut with a combination mower and binder; flowers by the use of hand scoop or seed stripper or rotary flower picker, and barks are removed by hand stripping using ordinary cutting tools. Underground plant drugs are collected by manual or mechanical digging tools like ploughs, hoes, potato diggers or tractors.
Time of Collection:
Natural drugs should be collected at the proper time since the nature and quantity of their active constituents vary greatly with season, time of the day and the age of the plant organ. The proper time is that period of growth or development of the Plant when it contains the highest quantity of the medicinal principles and when the collected material will dry to give a good appearance and ensure an improved keeping quality of the drug. The following are· general rules for collection of the plant drugs:
Leaves and flowering tops should be collected during the active reproductive process of the plant, i.e. from the beginning of the flowering to early fruiting. Since the photosynthetic process is most active in the plant during this period, the leaves and flowering tops contain the maximum amount of secondary metabolites.
Flowers should be collected prior to or just about the time of pollination, i.e. before they open or just star opening and collection should be affected in dry weather and towards the middle of the day.
Fruits may be collected when they are fully mature but unripe (e.g., Black pepper, Cubeb) or when fully ripe (e.g., Umbelliferous fruits).
Seeds should be collected when they are fully mature and have ripened, but before the fruits open.
Barks are generally collected at the end of the winter season and before the new growing season or vegetative process starts.
Roots and rhizomes of annual plants should be collected shortly before flowering, those of the biennials in winter at the end of the first year’s growth, and those of the perennials should also be collected in winter at the end of the second or third year’s growth or when the vegetative processes cease.
Influence of time of collection on the quality of drugs:
The time of collection of plant drugs from their natural sources influences their quality to a great extent. The following examples will illustrate this point:
Hyoscyamus and Belladonna leaves have been found to contain the highest amount of tropane alkaloids when collected at the beginning of flowering period, while the alkaloid content is highest in Stramonium leaves when the plant is in full bloom.
Stramonium leaves, collected in the morning, contain a higher proportion of alkaloid than those collected in the evening.
Full grown but green Conium fruits yield more than 3 percent of the alkaloid coniine, but the yellow or ripe fruits yield not more than 1 percent of the alkaloid, i.e., the alkaloid content reduced rapidly as the Conium fruits ripen.
Fully mature but unripe capsules of Papaver somniferu.m contain highest amount of morphine. The latex of its yellow capsules contains lower amount of morphine. Thus the latex of yellow capsules produces substandard Opium.
The unexpanded Santonica flowers yield as much as 3 percent of santonin, but as soon as the flowers mature or open up this anthelmintic principle rapidly disappears.
Closed Pyrethrum flowers produce the finest and most powerful insecticide powder, but the ones produced from the half-open or full open flowers possess less than half of its potency.
Treatment after collection:
Certain treatments are required for some drugs prior to drying. For most roots and rhizomes the following treatments are often necessary: (a) removal of adhering soil by washing and brushing, (b) cutting into pieces or slicing assist drying large and fleshy roots and rhizomes and (c) peeling and washing of fleshy rhizomes. For leaves: 9a) removal of large stalks, and (b) a brief process of fermentation or curing in some cases, e.g. Tea leaves. For barks (a) scrapping off of the cork and (b) covering the bark for a certain period of time to induce slight fermentation in cases like Cinnamon. Many other similar treatments are done to various drugs before they are subjected to drying.
Immediately after collection crude drugs should be dried to stabilize the condition of the drug and to fix their chemical constituents. Drying is also necessary to ensure good
keeping quality of the drug, to prevent moulding, to stop enzymatic hydrolysis, to discourage growth of bacteria and insects and to stop chemical and other changes in the drug. In order to preserve good quality in drug sent to the commercial market it should be dried in the proper manner using the correct temperature and the proper method. Drying at a higher temperature may destroy the active constituents of the drug, an_d when dried at a lower temperature over a long period enzymatic hydrolysis and other chemical reactions may take place in its constituents. The later method may also produce a partially spoiled drug with a dirty appearance, thus producing a lower quality drug. Such a product will not be well accepted by the prospective buyers. Drying is therefore a very important step in the preparation of a drug for the commercial market. A drug requiring slow drying should not be dried by artificial heat or direct sunlight. Coloured drugs, where retention of the natural colour is an important factor should always be dried in the shade. Drugs whose constituents are susceptible to enzymatic hydrolysis after collection must be immediately dried by using artificial heat. For example, enzymatic hydrolysis of the cardiac glycosides of Digitalis leaves starts as soon as the leaves are harvested. If these leaves are dried by the open-air method then most of their constituents will be lost resulting in a substandard drug. Therefore, for producing a good quality digitalis drug the leaves must be rapidly dried immediately after collection. This is possible only by the used of artificial heat in a mechanical dryer. Crude drugs of plant origin should therefore be properly dried to the required moisture level by employing the proper method of drying as dictated by the nature of the drugs and their desired appearance. In order to impress upon the importance of drying in the preparation of drugs for the commercial market the methods of drying collected plant drugs have been discussed below in some details.
Various factors related to the process of Drying of crude drugs are discussed below.