Pharmacognosy- 1 PHG 222 Prof. Dr. Amani S. Awaad Professor of Pharmacognosy Pharmacognosy Department, College of Pharmacy Salman Bin Abdulaziz University, Al-Kharj. KSA. Email: amaniawaad@hotmail.com
Preparation of crude drugs
*At the end of this lecture you should be able to know : How to prepare and collect plants Extraction methods of crude drugs Separation, purification and identification of active materials
Preparation of crude drugs To Prepare crude Drugs the following points must be fulfilled: 1- Selection& collection of promising plant materials. a. Suitable time for collection b. Methods of collection c. Authentication of plant material 2- Preservation of plant material A. Drying of plant materials i-natural drying ii- Hot air drying iii- Artificial drying ( freeze-drying). B. Stabilization C. Fermentation 3- Grinding of the dried plants 4- Storage &Packing of crude drugs 5- Extraction and fractionation i-what is a plant extract ii-types of the extracts iii-solvent choice iv-extraction parameters v-methods of extraction 6- Separation, purification and identification.
1. Selection &Collecting of medicinal plants I. Selection Before investing time, effort and money in phytochemical screening it is very important to select a promising plant. The choice of promising plant depends upon the following: 1- A plant which have a biological activity. 2- A plant used in folk medicine. 3- A plant which show a particular toxicities
II. Collecting 1. Collecting of medicinal plants Drugs may be collected from: 1- Wild plants. 2- Cultivated plants. Time of the day, time of the year and maturity Wild plant Cultivated plant Disadvantage 1- Scattered in large or unlimited area Advantage Present in limited area. 2- Difficult to reach Easy to reach 3- The collector must be highly skilled botanists 4- Deficiency may occur due to continuous collection The collector must not be skillful person Continuous supply
A. Suitable time for collection 1. Selection &Collecting of medicinal plants II. Collecting *The proper time of the day, time of the year and maturity stage of collection is particularly important because the nature and quantity of constituents may vary greatly in some species according to the season and time of collection. * The collected plant should be free from any contamination. * Collecting plants which are free from diseases (i.e. which are not affected by viral, bacterial, fungal infection). B. Methods of collection Medicinal plants must be largely collected by hand. This is especially true in the case of wild plants. With cultivation on a large scale, it may be possible to use modern agricultural harvesters.
1. Selection &Collecting of medicinal plants II. Collecting C- Authentication of plant material. This may be confirmed by: 1- Establishing the identity by a taxonomy experts. 2- Collection of a common species in their expected habitat by a field botanist. 3- By comparing the collecting plant with a voucher specimen ( herbarium sheet)
A. Drying of plant materials. Aim of drying: 1- Ease of transport. 2- Ease of grinding 3- Inhibit the growth of microorganisms. 4- Preservative of active constituents. 5- Enzymatic processes (in aqueous solution). 6-decreases the risk of external attack 2. Preservation of plant material Drying is done in i- Natural drying (Shade and in sunlight). ii- Hot air drying iii- Artificial drying ( freeze-drying).
i-natural drying: 2. Preservation of plant material A- Drying of plant materials. (Shade & sunlight) Shade drying requires full air circulation. It should not be undertaken inside conventional buildings but in an open-sided shed purposely built for shade drying Sun drying is most widely used method of drying plant but some times sunlight destroys the active constituents in the plants. Changes may occur during the drying: Size and weight, Shape and appearance, Color, Odor, Taste, Active constituent
ii- Hot air drying 2. Preservation of plant material A- Drying of plant materials. The most efficient drying is achieved in large driers of the tunnel type. The plant material is spread out on shallow trays, which are placed on mobile racks and passed into a tunnel where they meet a stream of warm air. The air temperature is kept at 20-40 C for thin materials such as leaves, but is often raised to 60-70 C for plant parts that are harder to dry, e.g. roots and barks
iii- Artificial drying ( freeze-drying). 2. Preservation of plant material A- Drying of plant materials. Freeze-drying (lyophilization). Frozen material is placed in an evacuated apparatus which has a cold surface maintained at - 60 to -80 C. Water vapor from the frozen material then passes rapidly to the cold surface. The method requires (1) a relatively complicated apparatus and (2) is much more expensive than hot-air drying. ( not used as a routine method, heatsensitive substances)
2. Preservation of plant material A- Drying of plant materials. B- Stabilization long storage, enzymatic reactions will slowly destroy the constituents (Bec. traces of water can never be removed). Stabilization is a process to destroy enzyme This process eliminates both bacteria and anthraquinones (laxatives) via a super chilled ethanol bath. In this cold bath, the stabilized aloe solids separate from water and ethanol Its value for the isolation of compounds that are very susceptible to enzymatic degradation e.g. aloe.
C- Fermentation 2. Preservation of plant material A- Drying of plant materials. Enzymatic transformation of the original plant constituents is sometimes desirable. The fresh material is then placed in thick layers, sometimes covered and often exposed to raised temperatures (30-40 C) and humidity, so as to accelerate the enzymatic processes. (This treatment is usually called fermentation). The fermented product must, of course, be dried afterwards to prevent attack by.
C- Fermentation 2. Preservation of plant material A- Drying of plant materials. Fermentation is mostly used to remove bitter or unpleasant-tasting substances or to promote the formation of aromatic compounds with a pleasant smell or taste. It is mainly applied to drugs used as spices or stimulants, e.g. vanilla, tea and cacao. CH 3 O Glu-O CH 2 OH Enz H 2 O Glucovanillic alcohol (glucoside) CH 3 O HO CH 2 OH Enz [O] CH 3 O HO Vanillin CHO
3- Grinding of the dried plants. 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 in 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 and large differences in particle size thus slow down the extraction process. Types of machines 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.
3- Grinding of the dried plants. Following grinding, the material must be sifted to ensure the proper particle size. Sifting can be performed according to two different principles: sieving and blast sifting. Sieving In sieving the material is passed through a sieve of suitable mesh size giving two fractions. The fraction passing the sieve consists of particles with a size smaller than or corresponding to the mesh size. The remaining fraction consists of coarser particles which are returned to the mill for continued grinding. Blast sifting In blast sifting the material to be classified is blown with compressed air into an apparatus which allows the particles to sediment according to their weight. Coarse, heavy particles settle fast whereas small, light particles stay for a long time in the air stream.
4- Storage &Packing of crude drugs Drugs containing glycosides and esters are usually less stable than those containing alkaloids. Drugs with essential oils deteriorate rather quickly through evaporation, oxidation and polymerization of the substances constituting the essential oil. Tannins on the other hand, have an almost unlimited durability. In order to keep crude drugs as long as possible: It is essential to store them in a dry condition in carefully closed containers at low temperature. 1. It is also advisable to exclude light, because - even if it does not affect the active constituents - it almost always causes changes in the appearance of the drug, especially loss of color. 2. It is also necessary to protect the drug against insect attack.
5- Extraction and fractionation i-what is a plant extract? A plant extract must be obtained from a solidliquid extraction. Solid-liquid extraction is defined as an operation to separate elements contained in a solid body by solubilization with a solvent, and it may be followed by purification. The extract is contained in the solvent. If the solvent is an edible solvent, it is not necessary to dissociate it from the extract. If the solvent is not an edible solvent, separation allows obtaining a dry extract.
5- Extraction and fractionation ii-types of the extracts 1-Dry extracts: all solvent has been removed. 2-Soft extracts & fluid extracts are prepared with mixtures of water and ethanol as solvent. 3-Tinctures are prepared by extraction of the crude drug (or plant) with 5 to 10 parts of ethanol of varying concentration, without concentration of the final product.
5- Extraction and fractionation iii-solvent choice The ideal solvent for a certain pharmacologically active constituent should be: 1. 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, volatile and harmless to man and environment. According to the pharmacopoeias, ethyl alcohol is the solvent of choice for obtaining all types of extracts. The ethanol is usually mixed with water to induce swelling of the plant particles and to increase the porosity of the cell walls which facilitates the diffusion of extracted substances from inside the cells to the surrounding solvent.
5- Extraction and fractionation iv-extraction parameters Extraction of plant materials is varied. It depends on different parameter such as 1- The texture of the plant material. 2- The water content of the plant material. 3- The type of substances to be extracted or nature of active constituents.
v-methods of extraction 1- Maceration powdered crude drug is placed in a stoppered container with the solvent and allowed to stand at room temperature for a period of at least 3 days. The mixture clarified by filtration 2- Percolation Percolation, on the other hand, is the method of filtration in which plant passed through solvent to take out their substance. 3- Infusion 5- Extraction and fractionation Fresh infusions are prepared by macerating the crude drug for a short period of time with cold or boiling solvent.
Methods of extraction cont.. 5- Extraction and fractionation 4- Digestion This is a form of maceration in which gentle heat is used during the process of extraction. It is considered as maceration but with relatively elevated temperature(35-45) 5- Decoction In this process, the crude drug is boiled in a specified volume of solvent - cooled & -filtered. (heat stable & continues) 6- Continuos hot extraction The powdered material is continuously extracted in a Soxhlet apparatus with suitable solvents. Avoid with heat sensitive materials
Methods of extraction cont.. 5- Extraction and fractionation 7-Counter-current Extraction In counter-current extraction (CCE), wet raw material is pulverized and produce a fine slurry. Here the material to be extracted is moved in one direction within a cylindrical extractor where it comes in contact with extraction solvent. The further the starting material moves, the more concentrated the extract becomes. Complete extraction is thus possible when the quantities of solvent and material and their flow rates are optimized. Finally, sufficiently concentrated extract comes out at one end of the extractor while the marc falls out from the other end.
Methods of extraction cont.. 5- Extraction and fractionation 8-Ultrasound Extraction (Sonication) the acoustic characteristics of any use to transmit information or to the related material, all known as ultrasound. Ultrasound is often used by the current frequency range of KHz ~ MHz, can enjoy the use of function and to determine the frequency of use. When the ultrasonic is propagating in the extracted liquid, the ordered and high-speed ultrasonic vibration will result in cavitations bubbles in a solvent material. When these bubbles collapse near the cell walls, the resulting shock waves and liquid jets cause those cells walls to break and release their contents into a solvent
Methods of extraction cont.. 5- Extraction and fractionation 9-Supercritical Fluid A supercritical fluid is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist. It can effuse through solids like a gas, and dissolve materials like a liquid. In addition, close to the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties of a supercritical fluid to be "fine-tuned".
Methods of extraction cont.. 5- Extraction and fractionation 10- Distillation is a process of separating the component substances from a liquid mixture by selective evaporation and condensation. Distillation may result in essentially complete separation (nearly pure components), or it may be a partial separation that increases the concentration of selected components of the mixture.
6- Separation, purification, and identification. The separation, purification and identification of the components of a mixture are among the everyday problems faced by both industrial and research chemists. This can be carried out using different method of chromatography
Extraction Solvent removal In-vivo Biological screening In-vitro Isolation &identification