Processing of herbal raw material


(T. Y. B. Pharm  Unit -I)
AS per PCI Syllabus

Processing of herbal raw materials



Cultivation of medicinal plants is also known as propagation, Which can be done by sexual and asexual methods. Processing of herbal raw materials involves various stages from which the crude drugs undergo after harvesting. It can be classified into primary and secondary processing which are further sub categorized as follows.



Primary processing


It includes simple procedures by which the herbs are prepared like sorting of different parts, garbling, cleaning, drying, etc. The details of these processes are as follows.
Garbling
Cleaning,
Drying


Garbling (Sorting)


This process helps in ensuring the purity and cleanliness of the harvested material. Dirt like soil, dust, impurities like insects, dead tissues and residual non medicinal plants are Separated from the raw material. The process depends on the part of the plant to be prepared. The process may involve procedures such as removing dirt and foreign Substances, discarding damaged parts, peeling of barks, sieving, trimming, removal of hairs from roots, removal of seeds from fruits, stripping of leaves from stems. This may be done by mechanical means but in some cases it is usually performed manually by hands.

Washing :


After garbling the herbal raw material should be cleaned well to remove the traces of remaining soil, dirt and other impurities from the surface. The roots, rhizomes and tubers are washed with clean water. During the washing process, scrapping and brushing may be necessary.

Parboiling (Blanching) :

After washing, certain herbal raw materials need to undergo parboiling process in which they are put in boiling water for a short period.
This may help in improving the storage life of the raw material and prevent insect/ mould contamination.
It may also facilitate in further processing such as removal of stubborn impurities as well as outer coats/ covering of raw materials.

Leaching :

Some impurities can be removed by subjecting the plant material under running water known as leaching. However the duration of leaching should be controlled to prevent the loss of chemical constituents present in the drug.

Drying :

In some cases, the plant material should be thoroughly dried after washing in order to prevent the deterioration and degradation of active constituents. They must be dried as soon as possible to remove moisture and reduce the damage due to microbial or mould infestation.
Drying also prevents the activation of certain enzymes which may otherwise degrade the active ingredients and also facilitate grinding and milling of the raw material. Depending on the drug & nature of ingredients, different drying methods can be used which are as follows.


I) Natural drying

a) Sun drying:
Most herbal raw material can be dried in open air under direct sunshine provided the climate is suitable. The duration of drying process depends on the physical structure of the plant material and weather conditions. The plant material should be spread out in thin layers, care should be taken to prevent contamination by diet. impurities. While drying the plant material should also be protected from insects, Birds, rodents, pests and other domestic animals. 
b) Shade drying: 

Some medicinal plants cannot be directly exposed to sunlight, hence need to be dried under shade. This drying process is slow but helps in minimizing loss  of  colour, volatile oils and aromatic components from being evaporated.

II) Artificial drying 
Drying by artificial heat is more rapid than open air drying and is necessary in rainy season and regions where there is high humidity. The temperature and equipment used for drying depends on the physical and chemical nature of the drug and its constituents. Various equipment's such as tray dryers, spray dryers, vacuum dryers are used. Over heating may lead to excessive loss of volatile components as well as decomposition of chemical constituents. The temperature should be kept below 60 0C wherever possible.


a. Tray dryers (Oven)

 The drugs which do not contain volatile oils and are quite stable to heat or which need deactivation of enzymes are dried in tray dryers.
In this process, hot air of the desired temperature is circulated through the dryers and this facilitates the removal of water content of the drugs (belladonna roots, cinchona bark, tea and raspberry leaves and gums are dried by this method).

  b. Vacuum dryers


 The drugs which are sensitive to higher temperature are dried by this process,
e.g. Tannic acid and digitalis leaves.

 c. Spray dryers
 Few drugs which are highly sensitive to atmospheric conditions and also to temperature of vacuum-drying are dried by spray-drying method. The technique is followed for quick drying of economically important plant or animal constituents, rather than the crude drugs.
Example: papaya latex, pectin, tannins, etc.

Secondary processing

The secondary processing differs from one herb to another depending on the nature of active ingredients as well as therapeutic properties. Secondary processing includes techniques such as removal of foreign substances, prevention of microbial / infestation, enhancing the efficacy of drugs, reducing the toxicity, extraction using suitable solvents, conc. & drying of extracts. These are further standardized by different methods.

Cutting, Sectioning and Communition :

After thoroughly drying, the herbal materials are processed by cutting and sectioning into smaller sizes which are convenient for storage as well as extraction. Various sizes can be obtained depending on the part of herb and extraction methods used. It may be small particles, coarse powder or fine powder.

Aging /Sweating :

Aging refers to storing the raw material for a specified time after harvesting.
It is generally done under sun or in shade for up to a year.
During the process of aging excessive water is evaporated & enzymatic reactions may occur to alter the chemical composition of herbal material.

Example:


Cascara bark should be aged for at least one year prior to use in medicinal preparations to reduce its irritant effects. Sweating is done by subjecting the herbal materials at a temperature between 45 to 65°C with high humidity for a period ranging from one week to few months. The herbal materials are stacked between woollen blankets or other kind of cloth. .The sweating process is considered a hydrolytic and oxidative process in which some of the chemical ingredients of the herbs are hydrolysed or oxidised. 

Baking / Roasting :
It is a process of drug heating where the herbal material is heated in ovens. The temperature of heating and duration of baking/ roasting vary from one herbal material to another until the drug develops a specific colour.
Example:
Nutmeg is roasted till they turn to yellowish brown colour.

Boiling / Steaming :


In the boiling process the drug is cooked in water or any other liquid solvent such as vinegar, wine, milk or animal urine.


Example:
Acorus calamus rhizome is boiled in cow’s urine to enhance its anticonvulsant effects. In the steaming process the herbal material is kept in contact with steam using a steamer resulting in development of moist texture. 

Stir frying:

 In the process in which the herbal materials are put in a pot of frying pan and continuously stirred or tossed for a specific period under heat until the external colour changes, charred or even carbonized. To facilitate uniform heating, the drug material can be admixed with sand, talc or clay.

Example: 
Liquorice roots and rhizomes are stir fried with honey.

Fumigation:

Sometimes the harvested raw materials are subjected to fumes. Fumigation with sulphur dioxide is commonly employed for some medicinal herbs for the purpose of preserving, colour, improved appearance, bleaching and preventing the growth of insects and moulds.

Extraction of herbal materials

Extraction is a process of separation in which the chemical constituents present in plant and tissues are removed by using selective solvents which is called as menstrum. Herbal extracts include infusions, decoctions, fluid extracts, tinctures and powdered extracts. The herbal preparation so obtained may be ready for use as medicinal agent or it may be further processed to finished products such as tablets, capsules and pills.

i. Infusion :


It is a liquid preparation obtained by extracting herbal materials with either cold or hot water without boiling. Other solvents may also be used.


ii. Decoction :

 

It is a liquid preparation obtained by boiling the herbal materials with water.

iii Fluid extract:

 

It is a liquid preparation obtained by maceration or percolation of herbal materials in alcohol. The ratio will be one part of liquid contain one part of herbs (1:1).


iv. Tinctures: 

It is a dilute alcoholic extract of herbal materials typically made up of 1 part of herbal material with 5 to 10 parts of the solvent.

v. Powdered extract:

  

It is a form of herbal preparation which is processed into dried, granulated or powdered materials