Collection, Drying, and Storage of Medicinal Plants PDF

Pharmacognosy Department, Faculty of Pharmacy, NINU university II. COLLECTION OF MEDICINAL PLANTS  Medicinal plants must be collected at the proper collection time and at the proper stage of development of the plant in order to ensure maximum quality and quantity of their active constituents...

Pharmacognosy Department, Faculty of Pharmacy, NINU university II. COLLECTION OF MEDICINAL PLANTS  Medicinal plants must be collected at the proper collection time and at the proper stage of development of the plant in order to ensure maximum quality and quantity of their active constituents 1. TIME OF COLLECTION a)Time of Year: The nature and the amount of active constituents varies throughout the year, e.g. The nature and the amount of active constituents varies throughout the year e.g. Rhubarb contains no anthraquinones in winter, but instead it contains anthranols, which are converted to anthraquinone compounds in summer. b)Time of Day: Ex. the percentage of cardiac glycosides in Digitalis leaves is higher when collected in the afternoon than when collected in the morning. It has been suggested that these glycosides undergo decomposition during the night and recombine again with the sugars resulting from photosynthesis during daytime. Ex. Also solanaceous leaves contain a higher percentage of alkaloids when collected in the morning than when collected in the afternoon.  2. STAGE OF DEVELOPMENT The percentage of active constituents of drugs depends on the stage of maturity and age of the plant, e.g. solanaceous leaves contain the maximum amount of alkaloids at the flowering stage and Santonica flowers are rich in the bitter principle santonin when they are non-expanded and show a decrease in the amount of this substance upon expansion. Leaves are collected at the beginning of the flowering stage, when they are in the most healthy state and contain the optimum percentage of their active constituents. Collection of leaves should be made in dry weather, since wet weather may cause deterioration and discoloration during the drying process. CONTINUE: 2. STAGE OF DEVELOPMENT Collection of Flowers : carried out in fine, dry weather in order to fix the color of the product. They are gathered just at the time of pollination, before the formation of fruits. Cloves are collected in buds, while Chammomile flowers are collected just after full expansion. Clove buds Chammomile flowers CONTINUE: 2. STAGE OF DEVELOPMENT Collection of Barks: is usually carried out in the spring or in the early summer, when the cambium is active and can thus be stripped off easily from the trunk and branches. For the removal of bark, longitudinal incisions are made at intervals, round incisions are made and the barks are stripped off in long pieces.  CONTINUE: 2. STAGE OF DEVELOPMENT Collection of Fruits: This is carried out near the ripening season, when they are fully mature but not completely ripened (when attaining the full size). They must be gathered in dry weather. Collection of Seeds: The fruits are collected at the ripening stage. The mature seeds are separated from the pericarp and collected. fenugreek Underground organs (storage tissues) e.g. roots, rhizomes, bulbs, and corms should be collected in autumn or winter. ginger Liquorice rhizome root  CONTINUE: 2. STAGE OF DEVELOPMENT Unorganized drugs, e.g. resins, gums, latex, etc. should be collected in dry weather. Gum Acacia Opium latex Resin Unorganized drugs are obtained by making certain incisions in the plant and the resulting drug usually acquires the shape of the incision.  TREATMENT OF DRUGS BEFORE DRYING  Cleaning: Underground organs, need cleaning and garbling prior to the drying process.  The cleaning process includes the removal of soil particles from drugs by shaking, brushing, or washing under a stream of water.  Garbling: is the process of removal of foreign matter such as sand, dirt or other parts of the plants from the drug. This can be achieved either by hand or by a special machine. Metallic particles can be removed by passing the drug over a big magnet.  The complete removal of foreign material is not practical, so pharmacopoeias state certain limits of them.  DRYING OF CRUDE DRUGS  Fresh plants usually contain a high percentage of moisture (up to 80 or 90%)  Drying is the removal of water or most of it. The duration of the drying process varies from a few hours to many weeks.  Moisture must be removed in order to: 1. Stop the enzymatic action that may change the active constituents. 2. Avoid deterioration upon storage by preventing the growth of microorganisms (bacteria and fungi). 3. Facilitate grinding of the drug that facilitate better handling 4. Facilitate packing and storage. 5. lower the transportation cost as the weight of the drug is greatly reduced.  CONTINUE: DRYING OF CRUDE DRUGS  Careful drying is also essential in order to obtain drugs which: 1. Retain their physical characters. 2. Retain their chemical constituents. 3. Comply the pharmacopoeial requirements for maximum moisture content.  The most important factors in drying process are temperature and time:- To use as low temperature as possible. To carry out the operation as rapid as possible. CONTINUE: DRYING OF CRUDE DRUGS  If an enzymatic reaction is required, the drying process is carried out slowly as in case of Vanilla pods. Vanilla pods  If enzymatic hydrolysis is not desired, drying must be carried out as quickly as possible as in case of digitalis and drugs containing volatile oils. Digitalis purpurea   Methods of Drying:  I. Natural drying: By natural air in sun (in cases of the plants which are not affected on direct exposure to sun, heat and light e.g. Senna leaves) or in shade e.g. flowers whose color is destroyed by direct exposure to sunlight.  This method dries the plant very slowly. II. Artificial drying: Rapid method, immediately stops enzymatic action & carried at well controlled temperature:  1. Direct fire. done very carefully to prevent damage of the drug.  2. Stoves.  3.Drying chambers: It is a controlled and most preferable method for drying, where drugs are placed on shelves in chambers possessing openings which allow entrance of a warm stream of air through an inlet near the floor and exit of the moist warm air through an outlet near the roof. II. Artificial drying: 4.Vacuum drying: It is used for drugs which are sensitive to high temperature. The chambers are air tight and connected to an efficient vacuum pump. As the pressure is lowered, the water content of the drug is removed at a higher rate at lower temperature, e.g. Digitalis leaves.  5. Freeze drying or lyophilization: This method is generally used for drying extremely delicate products such as coffee extracts. The principle of this process is the removal of the water content of the drug when present in the frozen state under vacuum at which it sublimes into vapours directly without passing through the liquid state.  1. Size and weight: Drugs get smaller in size due to loss of water and they lose 80-90% of their original weight.  2. Shape and appearance: Most drugs shrink when dried and the surface gets wrinkled or reticulated. e.g. the inner surface of most barks gets curved, as the inner tissues are soft and the outer ones are hard.  3. Texture: Fresh organs are generally firm. On drying, drugs become harder, e.g. roots and leaves become brittle and drugs containing starch become horny due to gelatinization of starch.  4. Colour: Generally, drugs become darker in color upon drying (Tea leaves change from green to dark brown), but in certain cases, a total change may occur, e.g. the green color of certain drugs changes to brown on drying due to decomposition of chlorophyll. Flowers may lose their color, especially when red or blue, due to destruction of the anthocyanin producing these colors.  5. Odour: In certain drugs, drying changes the natural odour, e.g. Digitalis and Hyoscyamus lose their bad odours when dried. Vanilla pods are odourless when fresh but they acquire a fragrant aromatic odour upon drying due to the liberation of vanillin.  6. Taste: The taste of the drug may be altered on drying, e.g. Gentian is very bitter when fresh , becoming pleasant on drying.  7. Constituents: When the changes in active constituents are desirable, the drying process is carried out slowly to allow optimum change of constituents. On the contrary, when the changes in active constituents are undesirable (as in case of Digitalis leaves), drying must be carried out quickly to prevent enzymatic hydrolysis.  7. Constituents: An example of the desirable changes is the hydrolysis of the glycoside glucovanillin to vanillin upon drying vanilla pods. N.B. when enzymatic reactions are not desired, drying should occur as soon as possible after collection Drugs containing volatile oils gradually loose their aroma on storage.  Drugs may gradually deteriorate during storage if they are stored under uncontrolled conditions. Few drugs, e.g. Nux vomica are not affected. Sometimes, storage improves the quality of certain drugs such as Frangula and Cascara barks. Generally, changes occurring upon storage are undesirable. Examples are:  Aromatic drugs usually lose their aroma.  Ergot may acquire a disagreable odour.  Drugs containing fixed oil may become rancid.  Volatile oils may be resinified.  Digitalis and Cannabis may lose their active constituents. For the above mentioned reasons, detailed instructions for storage of drugs are listed in most pharmacopoeias. 1. Physicochemical factors: a)Moisture: This may cause hydrolysis of the active constituents by enzymes, e. g. Digitalis leaf and aids the growth of bacteria and fungi. To overcome the effect of moisture, By storing the drugs in containers enclosing dehydrating agents such as quick lime or calcium chloride (temporary), or by destroying enzymes by subjecting the fresh drug to alcohol vapour or immersing it in alcohol (complete). b) Temperature: A slight rise in temperature above normal will activate enzymatic action, which usually occurs at about 35 to 45 C. Drugs containing volatile oil, e.g. Ginger, Clove and Chammomile are directly affected by rise in temperature. 1. Physicochemical factors: c) Light: This affects delicate drugs, e.g. rose petals which are red when fresh change to brown on exposure to light and Digitalis leaves may lose their active constituents on exposure to sunlight. These drugs must be stored in dark brown containers away from light. d)Air: Oxygen of air has a definite oxidation effect on the active constituents of some drugs, such as fixed oi in Linseed oil. The general rule for preservation of drugs is to store them in moisture- proof, air-tight containers at low temperature. In a few cases, the drug may be kept in nitrogen atmosphere 2. Biological factors:  The biological factors producing deterioration of most drugs are bacteria, moulds, fungi, insects and mites. These may change the physical properties of the drug, such as colour and texture.  Moulds and fungi usually attack drugs rich in nutritive substances, such as bulbs, corms, roots and rhizomes, if they are not stored properly. This may lower their content of active constituents.  Insects attack nearly all drugs in powdered form, rendering them unsuitable for preparation of standard extracts. Insects should be destroyed before storage of drugs.  Rodents also cause much spoilage of crude drugs during storage, if the herbal plants are stored in paper, cloth, or wooden containers. This may be eliminated largely by packing and storing the drugs in glass, plastic, or metal containers. Rodenticides may be used. 2. Biological factors:  Methods for controlling insects  Heating the drugs to about 60 to 65 C to kill the eggs of insects. In some cases, heating may affect the active constituents of the drug, so this method is not suitable for all drugs.  Fumigation of drugs by using various volatile insecticides, such as carbon tetrachloride, carbon disulphide or a mixture of methylene oxide and carbon dioxide. Most fumigants do not kill the eggs, so the drug must be fumigated at intervals. Fumigants must be applied carefully because they are poisonous.  Liming: This is used for a few drugs, such as Ginger and Nutmeg. This blocks the respiratory system of insects and larvae, so they die after some time.  Low temperature storage: preferred over the previous methods as it destroys insects, larvae and eggs.