Wednesday, February 18, 2009

Herbal Extracts; Solubility and Distillation


The fields of organic chemistry and herbalism are intimately linked. Early healers were both botanists and chemists. Now it seems the two fields of herbalism and chemistry have become schismed in some minds and the word chemical has taken on a negative connotation. Some people even boast that their products are ‘chemical free’; impossible I say!

Since I am often asked about herbal extracts I wanted to address that issue. To extract means to obtain from a substance; primarily by chemical or mechanical action. Before making an herbal extract you first need to consider the chemical and physical properties of the substance you want to extract from the herb.

Most extractions are based on solubility of the chemicals of interest. The most common herbal extract is a tea (or tisane). This type of extract is based on water solubility. If you pour water over an herb and let it steep, the water soluble chemicals of that herb will be released or dissolve into the water. This process is speeded up with heat. Water is a polar substance and will extract other polar substances. Examples of polar substances include flavononids (pigments) and polyphenols, organic acids (formic acid, acetic acid, glycolic acid, lactic acid), sugars and glycosides. A water extract is the best way to isolate the antioxidant properties of flavonoids.

The other most common herb extract is based on solubility in oil rather than water. We know oil and water do not mix (think of salad dressing). This is because water is polar and oil is nonpolar. Herbs are often extracted into almond oil, olive oil or grapeseed oil. An extract in oil will release the oil soluble or nonpolar chemicals of the herb such as fatty acids, lipids, carotenoids (lutein, zeaxanthin), tocopherols (vitamin E) and other oil soluble vitamins, terpenes found in essential oils. If you want to extract carotenoids from an herb, an oil extract is the best way to go.

Other solvents such as ethanol, hexane or CO2 can extract some chemicals that are polar and some that are nonpolar. Hexane is an inexpensive method of extracting large quantities of nonpolar molecules and can form concentrated mixtures; more so than extracting in oil. Hexane will also dissolve some small polar molecules that are soluble in water. We won’t go into safety issues here.

One other method of extracting chemicals from plants is by distillation. Distillation has not much to do with solubility but rather vaporization points. It allows a volatile substance to be separated fro a non volatile substance. Distillation is probably most widely used for producing alcoholic beverages after fermentation of plant sugars by yeasts. Ethanol boils at 78ºC while water boils at 100ºC. Because of its lower boiling point, ethanol will begin to boil and evaporate (turn to gas) when heated before the water does. Using a proper apparatus to collect and condense the steam, ethanol will be separated from the water. This process is of course not complete because much of the water will evaporate at the same time. Below is a picture of a basic distillation unit.



Herbal components can be separated by distillation in the same manner. Water and herb are put together into a flask or pot and heated until the temperature reaches a point where steam is formed. The steam as well as anything with a boiling point near that of water will evaporate (turn into gas) to enter the column part of the still and then the condenser to return to a liquid form. Herbal compounds that enter the distillate portion include a complex mixture of essential oil, water, and organic plant acids. If enough volume is distilled, eventually the distillate will separate out into oil soluble and water soluble components with the essential oil floating on top of the water soluble components. The watery portion of the distillate is considered waste by many large manufacturers of essential oils. However, many smaller companies (Sagescript included) distill primarily to obtain the watery distillate. These herbal distillates are often called hydrolats, herbal waters or hydrosols. So the alchemist (or spagyric) and the chemist are none to different.
Part of this article was extracted from a presentation I gave at the International Herb Association, 2007.

3 comments:

Wild Rose said...

What a great article Cindy. Thanks for sharing your knowledge with us.

Marie

Herbal Extracts said...

Nice article.. Thanks for given information..

Beth said...

Very good article! I have long wondered which menstruum is best for any particular herb. This helped.

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