Botanical Basics: Botanical Extracts: Not Single Chemical Ingredients(Extraction methods and information you need to know)
Understanding botanical extracts requires understanding solvents, extract ratios and extract semi-purification.
By Steven Dentali, PhD, American Herbal Products Association
In my last column (January/February issue) I discussed the chemical complexity of botanicals and what’s in a botanical name. In our industry, a single name can refer to the raw material, the ingredient or the finished product. For example, “coffee” can mean the live plant, the dried bean, the drink in a cup or even a “let’s do coffee” event.
My focus this time is on another term: “extract.” An extract is not the dried, ready-to-ship agricultural commodity known as the crude botanical. It’s also not a finished product. Instead, extracts are herbal-product ingredients, and they can be of many different types.
There is so much to say about extracts that it’s impossible to cover it all here. However, a few basics include the solvent used to make an extract, the herb-to-extract ratio and the degree of extract purification. This last consideration can be thought of as how closely an extract represents the source plant from which it was made. The use of the term “extract” here is not to be confused with the product of juice extractors. While apple juice and carrot juice are extracted from apples and carrots, respectively, that’s not what is meant here. Instead, for our purposes, an herbal extract is the result of a solvent acting on plant material and dissolving some of its components. That solution, once separated from the insoluble plant materials, is the extract that can be left in liquid form, or the liquid removed to produce a solid extract.
Another way to define an extract is to consider what it is not. For example, it is not the material thrown away after extraction, which is known as the marc. It is not the equivalent of coffee grounds or spent tea leaves. Just as a cup of tea is no longer just the water, the extracting solvent is transformed into something that contains materials extracted from the source botanical—the extract. As such, it has a new identity, just as water becomes coffee or tea after extracting phytochemicals from beans or leaves. And just like those beans and leaves, most dried herbal materials have a limited shelf life. However, extracts of herbal materials are often stable for much longer than the raw materials. Thus, relocating a plant’s constituents from the plant into an extract can make good economic sense that also allows for shelf stable medicines and supplements.
Fluidextracts, Tinctures & Solvents
Perhaps the simplest extracts are those historically made with ethanol and water, where only the form of the medicine was changed to create an extract with all the bioactive properties of the starting plant. The United States Pharmacopeia described fluidextracts as liquid preparations containing alcohol as a solvent or preservative, or both, that are made so that 1 ml of the liquid contains the therapeutic constituents of 1 gram of the standard material used to make it. That is equivalent to one part (by volume) of the liquid extract having the same bioactivity as one part (by weight) of the starting herb. It’s a 1:1 ratio, where only the form has been changed from an herb to a liquid extract—from tea leaves to tea, so to speak.
Extracts can be thought of as the result of freeing up or making available the active materials from herbs into a more convenient dosage form. Fluidextracts were recognized as medicines that were easy to make, use and transport. They could also be administered in drop-by-drop doses that are immediately absorbed into the body.
Tinctures, another form of liquid extract, are essentially dilute extracts. Historically, they were made with a ratio of 1:5 or 1:10, where one part by dried weight of the herb was represented in 5 or 10 parts by volume of tincture.
As should be obvious by now, solvents are used to make extracts. In its 2003 white paper on the standardization of botanical products, the American Herbal Products Association (AHPA) defined an extract as follows: “The complex, multicomponent mixture obtained after using a solvent to dissolve components of the botanical material.”
Solvents may be used to extract as wide a variety of constituents as possible, or they may be chosen for a more selective action. Hot water is better at extraction than cold water. Alcohol (ethanol) has different properties than water and can therefore extract different constituents than water. A mix of water and alcohol is generally better at extracting a wider variety of constituents than either one alone. The ratio between water and alcohol is varied to suit the particular plant being extracted. The choice of solvent helps to determine exactly what and how much of an herb gets extracted from the plant into the extract.
The herb-to-solvent ratio describes how much herb was used to make a specific amount of extract, which is the same as how much starting material is represented in the final extract. As already discussed, fluidextracts represent a 1:1 ratio of herb to extract with traditional tinctures typically found in ratios of 1:5 or 1:10. Liquid extract ratios are often a measure of dilution. Partial or complete removal of the solvent from a liquid extract concentrates the extract into a semi-solid or dry form where the extract ratio now represents a concentration with the herb to extract ratio exceeding 1:1.
For example, if the solvent in a liquid extract makes up 80% of the extract, its removal concentrates the extract by a factor of five and makes a final herb to extract ratio of 5:1. There is a practical limit to how much an extract can be concentrated because plant constituents take up space in solid form. Because of this, higher herb-to-extract ratios don’t necessarily mean a more concentrated extract. More likely, they indicate a semi-purified extract or an inefficient extraction.
Degree of Extract Purification
AHPA has defined full-spectrum extracts as “comprising the complete range of soluble constituents native to the plant.” Fluidextracts and tinctures are designed to carry, or dissolve into the solvent, the complete range of soluble constituents found in the plant. That’s the idea. As mentioned earlier, for practical purposes, it’s often better to store and use plant extracts instead of the crude plants. This “improvement” of plant material makes complete sense when you are after the activity of the whole plant and not an isolated constituent. Isolated constituents, and arguably narrow selected ranges of constituents, are sometimes best thought of as extracted from plants instead of extracts of them.
If particular chemicals or constituents in a botanical are the only items of interest, then the botanical source might be immaterial. If all you want is the alkaloid caffeine, for example, it can be extracted from coffee, tea, yerba mate, guaraná, or even synthesized. Once purified, caffeine is pharmacologically equivalent regardless of where it came from. Plants and their full-spectrum extracts are not single constituents. They are complex mixtures that cannot be adequately defined by a single compound. Their makeup is a direct result of the starting material, the extraction solvent and the extraction conditions used to make them.
There is middle ground for extracts that falls between a full-spectrum extract and a single, purified constituent. The extracts that occupy this space defy simple categorization because they represent a continuum based on their chemical complexity. A broad or wide-spectrum extract contains a large array of extracted constituents, while narrow-spectrum extracts have a much simpler chemical makeup. A narrow-chemical-spectrum extract can be either a semi-purified one that originally had a wider variety of constituents or one made with a solvent that is relatively selective in what it extracts from the starting material.
The Middle Ground
When the bioactive materials in an herb (what’s in them that make them “work”) are unknown, it makes the best sense to extract as much of the herb as possible. This is most often the case for herbs, as it is for food. Dietary supplements made of vitamins and minerals are intended to supplement the diet; they are not food replacements, because foods are more than their constituent vitamins and minerals. In the same way, herbs are more than the relatively few constituents that can be identified in them; so in most cases, a wide-spectrum extract is the way to go.
Sometimes though, we do have an idea of which constituents are responsible, in whole or in part, for the bioactivity of a plant. In these cases, it may make sense to narrow the range of materials in an extract that originate in a plant. For example, it is known that the anthocyanin fraction of bilberry fruit is biologically active. The same is true for the silymarin complex from milk thistle seeds. Commercial extracts optimized for anthocyanin and silymarin complex content, respectively, do not represent the full complement of materials that can be extracted from the source botanical. However, they are not single isolated constituents either; they are somewhere in the middle. This fact will affect the herb-to-extract ratio and can drive it much higher than 5:1.
Are Higher Extract Ratios Better?
A kilogram of all the extractable material from bilberry fruit would include sugars and many other constituents along with anthocyanins. Thus, it takes much more fruit to produce a kilo of just the anthocyanin fraction of bilberry, so the ratio of fruit to extract goes up when an extract is semi-purified to focus on that single constituent class. A 50:1 extract doesn’t mean that all the extractable material from 50 kilos of starting material winds up in a single kilo of finished extract. It can’t. There isn’t enough room. The result of a 50:1 extract ratio is that some constituents are left behind in the process of semi-purification or aren’t extracted in the first place.
If five kilos of dried herb produce one kilo of dried extract, then the herb-to-extract ratio is 5:1. Ten kilos of that same dried herb should produce two kilos of extract. If only one kilo is obtained, then something went wrong with the process. A higher herb-to-extract ratio does not necessarily mean a stronger extract. To get a higher ratio than is normal from an exhaustive extraction means that either the extraction process wasn’t complete or that some of the extract was discarded in a process of semipurification. A semi-purified extract takes more starting material to get the same amount of finished extract than a full-spectrum one.
AHPA’s Standardization of Botanical Products: White Paper, published in 2003, provides the example of the silymarin complex from milk thistle seed as a semi-purified extract. The concentration of silymarin complex in the seed is about 1%, but through semi-purification, where other constituents are discarded, this concentration can be raised to about 80% in the finished extract. This process requires about 100 kilos of starting seed material to make one kilo of silymarin complex. That results in an herb-to-native-extract ratio of about 100:1. It should be recognized that the addition of excipients and other materials to an extract can lower the herb-to-finished-extract ratio considerably.
For additional information on extracts and to gain a richer understanding of the practical industrial aspects of what they are and how they are made, see AHPA’s 2001 Guidance for Manufacture and Sale of Bulk Botanical Extracts. Anyone that needs to be knowledgeable about extract quality should be familiar with the content of that guidance.
My next column will go a bit deeper into extracts by exploring the connection between strength, potency and standardization with the goal of better understanding the relevance of constituent percentages in the marketing of extracts to manufacturers.
Steven Dentali, PhD, chief science officer of the American Herbal Products Association (AHPA), Silver Spring, MD, studied herbal medicine in the Pacific Northwest, finding a disconnect between the herbal and academic communities. He subsequently earned his doctorate in Pharmaceutical Sciences with a specialization in Natural Products Chemistry from the University of Arizona, Tucson. An American Foundation for Pharmaceutical Education Fellow, Dr. Dentali is recognized as a foremost expert in the natural products industry. He is a member of the United States Pharmacopoeia 2010-2015 Convention, Editorial Board Chair of AOAC International, and is an advisory board member of the American Botanical Council and the American Herbal Pharmacopeia. A frequent lecturer, he also serves as a reviewer for the National Center for Complementary and Alternative Medicine at NIH. He can be reached at firstname.lastname@example.org; Website: www.ahpa.org.