SIA3 Extraction of Herbal Material

Herbs In Africa
Extraction of Herbal Material
Part 3
Part~1     Part~2     Part~4     Part~5     Part~6
by
Ivor Hughes

Extracting with Solvents

Apart from the crude drugs, the base materials of compounding, are its  solvents and carriers. The solvents are alcohol (ethanol) and distilled water.  The carriers are solutions, emulsions, mucilages, syrups, water and alcohol. An essential part of some carrier substances are the fixed oils and waxes. By far,  the most important substance is alcohol, without it, a complete extraction of  herb constituents is not possible.

Solvents used for Extraction Purposes

From the standpoint of pharmacy, the purpose of a solvent is to remove from a  solid, either in part or in its entirety, such substances that may be rendered  to a liquid. In chemistry the solvent is known as the ‘SOLUTION’ and the extracted material as the “SOLUTE’. In pharmacy the solvent used for extraction  is referred to as the “MENSTRUUM’. When the material has been extracted, the  menstruum is known as the “VEHICLE’ or “CARRIER” of the extracted material.

The use of solvents allows quite precise manipulation of herbal material and  without their use, herbal therapeutics would not have advanced far beyond a  primitive art. Solvents of various kinds are in widespread use throughout  industry and many households, in the form of stain removers and oven cleaners,  etc. Solvents differ widely from each other, not only in differing boiling points, but how they act or react with substances in which they come in contact.  In order to maintain the synergy of herbal preparations, it is vitally important that the plant compounds do not decompose, dissociate or complex when in contact with a solvent.

Solvents used for Herbal Preparations

The majority of solvents are toxic to a greater or lesser degree. It should also be remembered that it is not possible to remove all traces of a solvent from an extracted substance. There are no perfect solvents, each one has its  drawbacks. When considering the suitability of a solvent it should meet the  following criteria;

Alcohol

The alcohol of the British Pharmacopoeia, is a 95% mixture of ethanol and  water, which is obtained by the distillation of fermented sugars or by synthesis. It is a clear, colorless, volatile liquid. It has a burning taste,  with a characteristic odor and boils around 78°C. It is miscible with water in all proportions, however, when mixing with water, a contraction of volume and a  rise in temperature occurs. The mixture must cool to 20°C before it is adjusted  to its final volume. Its Specific Gravity (SG) at 20°/20°C (atmosphere 20°C –  liquid 20°C), is 0.8119, for practical purposes we can say 0.800, its molecular  formula is
C₂H₅OH.   

Synthetic alcohol can be manufactured by various chemical routes, from  different starting substances including ethylene, ethyl amine or ethyl iodide.  The most common starting substance is ethylene which is converted to ethanol in  the presence of water and sulphuric acid. 

The alcohol produced by such methods is cheaper, and therefore, attractive.  On analysis, its formula is C₂H₅OH. The physiological effects are manifestly different to those of alcohol produced by fermentation  methods. What is produced is determined by the strain of the yeast and the material (substrata) upon which the yeast must work. The perfumers preference,  is for a grain based alcohol to produce the ethereal and elusive top notes of  fine perfumes. Whereas, for the herbal pharmacist, a fruit or herb based alcohol is the preferred solvent.

Alcohol from Carbohydrate

The carbohydrates are found as complexes in all higher plants, those that  occur in the lower plants, such as the ferns, mosses and their allies, are  substantially the same, therefore, with the correct treatment, we may use them  as fermentation substrata, with or without, the addition of sucrose. Remember  that carbohydrate synthesis in plants is photosynthesis. This is an important  point for the Spagyric Pharmacist, because the alcohol used to extract a plant,  is made from the same species. The following table may be used as a rule of  thumb to estimate the amount of plant material required, to produce a given  amount of alcohol.

The rule is; that all such plant parts must be treated with amylase  to convert the carbohydrate to fermentable sugars. We may see from the above  table, that the leaf part of the plant contains the least amount of  carbohydrate.

Enzymes

The conversion of sugars by yeast to alcohol, is performed by enzymes; over a  dozen have been identified; the total of which is called the ?ZYMASE COMPLEX’,  all of which are involved in the fermentation process. Not all of the functions  are understood. The most important enzymes, from the alcohol production point of  view, may be summarized as follows.

It should be understood, that the clear cut divisions between substances and  sugars that are shown in table only indicate the major type of sugar to be found  in a plant, for they will undoubtedly contain a complex of sugars.

Production Routes

Honey, Malt or Molasses may be treated as mono-saccharide. Commence the  process at the 2nd treatment.

Remember the amylase, like yeast is heat sensitive, therefore, a poly-saccharide liquid should be allowed to cool to 25°C before adding the amylase.  To test if the starch has been converted to sugars, half fill a test tube with  the liquid and add 1 or 2 drops of tincture of iodine. If the starch is present  it will be indicated by a purple/black color change. If a significant change is  noted, leave the ferment liquid for a few hours longer to allow the amylase to  complete its task. If the color change is persistent, add more amylase. When the  fermentation has ceased the resulting liquid is then distilled.

Distillation

Distillation is an ancient technique known to many cultures. Western science  historians usually credit its discovery to the Arabs in the 11th or 12th century  AD. However translations of far older Indian and Chinese medical documents  mention products that would need spirits of wine to produce. Therefore would it  be reasonable to assume the technique arrived in Arabia from points East and  then percolated into Europe, via Spain, which then, were strongly influenced by  Arab culture.

It is a fact that all of our technology is no more than a shadowy reflection  of a natural process, e.g., distillation is a micro emulation of the planetary  rain cycle. The essential process involves a reversible change of state,  i.e., Liquid –>,Vapor–>, Liquid    

A liquid is subjected to heat to produce a vapor. The vapor is then rapidly  cooled to produce a liquid. The apparatus used in a laboratory is known as a  distillation train.

Fractional Distillation

Fractional distillation is another technique which is used to separate the  different components of a mixture. Separation may also be achieved by simple  distillation, but the technique is discontinuous and can become tedious. Whereas  the fractional technique is a continuous process that conserves time and  energy.  

In herbology, the major use to which the technique is put, is for the  fractional distillation of ethanol. However, for more advanced work, fractional  distillation under reduced pressure may be used for certain of the perfume oils.  And for the production of granulated extracts.
The preparation of ethanol,  employing the simple distillation technique, will on condensation produce a  liquid which contains some 60 to 70 % water, depending on the care taken. Water  evaporates at all temperatures above 0°C and water vapor will be carried over  with the ethanol.  

The collected distillate must then be redistilled a number of times to free  the ethanol from as much of the water as possible. Traditionally the old  herbologists would distill seven times. However, by employing a fractional  column, high strength ethanol may be produced in a single distillation. From the  95% alcohol we produce the purified or rectified spirit of the Pharmacopeia,  which is 90% alcohol freed from impurities and fusel oils; the diluting medium  is double distilled water.

Library
Part~1       Part~2     Part~4      Part~5     Part~6

The Pharmageddon Herbal
 The equivalent of a 3 year certificated course in Western Herbology, Save yourself thousands.
 

These articles have been published in
Science In Africa www.scienceinafrica.co.za
Next in this series: Dehydration Apparatus