Feature

Herbs in Africa
Part 3 -Extraction of Herbal Material

Ivor Hughes
www.herbdatanz.com

Part three in a series of articles which outline the basic requirements, for small scale, sustainable cultivation, and processing techniques, for rural communities continues. Links: Part One, Part Two.

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;

1~ It should display low toxicity to higher life forms.
2~ It should not cause the extract to complex or dissociate.
3~ It should be preservative in action.
4~ It should promote rapid physiologic absorption of the extract.
5~ It should be easily evaporated at a low heat.

Alcohol (Ethanol) will meet all of the above 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.

For Part 4, link here.

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