Essential oils have rapidly gained popularity in recent years, and many people see a bottle of essential oil as a liquid version of that same plant’s herb. This misconception leads to the unsafe use of essential oils, such as neat application and ingestion. This paper seeks to demonstrate the very significant differences in the chemistry of an herb, and the chemistry of that same herb’s steam distilled essential oil using three examples: peppermint, ginger, and anise. Each come from a different plant family, utilize different parts of the plant, and have very differing characteristics. But the three will collectively prove the point that an essential oil is certainly not a liquid version of the herb from which it was distilled. In order to understand the details, a review of necessary basic concepts has been presented:
General Chemistry and use of Herbs
General Chemistry and use of Essential Oils
A look at Peppermint, Ginger and Coriander
Overview of Herbs, Essential Oils, and Solubility
First, it is important to understand what an herb and essential oil is, along with the chemistry, different ways herbs and essential oils are prepared, and variables affecting a preparation like solubility, drug extract ratio, and concentration of active constituents. This information is an important part of demonstrating the difference in constituent content and identifying the best preparation and usage guidelines of an herb versus an essential oil from the same plant. The second part of the paper will look at specific herb examples: peppermint, ginger, and coriander. Most significantly, typically only about 1% of a fresh herb is made up of lipids, representing essential oils and other fat soluble constituents. Further, the fat soluble constituents will usually have a much smaller therapeutic margin than that of the whole plant.
What is an Herb? An herb is a plant used in phytotherapy to prevent and treat disease. Herbal drugs can be gentle or very powerful based on their chemical components. They can be used to treat whole body wellness, or a specific symptom, and like drugs, they have a therapeutic margin, contraindications, drug interactions, and potentially undesirable side effects. According to Weiss and Fintelmann (2000), herbs with very potent active constituents also run the risk of having greater side effects, and its is important to stay within the guidelines of the maximum permissible dose (amount in one dose, number of doses per day, and for what duration of time) based on weight, age, and overall health.
What is an Essential Oil? An essential oil is a highly condensed form of plant matter extracted from special secretory glands within the plant that could be located in various parts such as the petals, fruits, leaves, wood, or roots. These secondary metabolites are produced by the plant for various reasons such as to detract insects and herbivores, to protect from disease, or to reduce the growth of other plants nearby. Not all plants produce essential oils, and some produce oils that can be very toxic, like sassafras, pennyroyal, and thuja. Essential oils are extracted typically by steam distillation, in which only the highly volatile constituents with a molecular weight under 250 are kept, leaving all heavier components and plant matter behind, and typically only representing about 1% of the plant (Clarke, 2002). Thus, an essential oil’s chemistry can be quite different than that of the overall herb.
What is Solubility? When assessing the chemistry of herbs and essential oils, and the best method of preparation, it is important to to consider if components are either water or fat soluble. Water soluble plant matter dissolves best in water and travels thru the body via the bloodstream. Fat soluble plant matter prefers to mix with oil and collects in the body’s fat tissue and liver. Compounds in an herb can act as a solvent to bring fat soluble constituents into water, but some of the fat soluble components will be lost in the process (Witchl, 2004). Further, plant matter can be soaked in alcohol, vinegar, or vegetable glycerin to retrieve both the fat and water soluble components. Essential oils are fat soluble constituents of a plant or herb, but there are many other parts of a plant that are water soluble. Preceding is a review of the types of components of an herb and its corresponding solubility.
Components of an Herb
Fresh herbs researched were primarily composed of water, then carbohydrates (including fiber), about 10% proteins, and about 1% fat content. Dried herbs were lower in water content and thus higher in carb, protein and lipid content. (See Appendix 1 – Pie Chart of the Composition of Herbs). As it relates to the key therapeutic components of an herb, there are the following categories:
Methods of Preparing of Herbs, Including the Steam Distillation of Essential Oils
Teas, Infusions, and Decoctions: Water based infusions and teas extract glycosides, alkaloid salts, and that which is water soluble. Related to solubility it is important to understand that not all fat soluble components of an herb are recovered in a tea / water based preparation. Some compounds in an herb can act as a solvent to bring hydrophilic constituents into water, but some essential oil is lost in the process. Particle size of an herb preparation is important; smaller ground herb pieces increase surface area, which can increase the amount of components extracted. However, cut plant parts stored over time loose volatile oils, that can also become oxidized (Witchl, 2004). For example, making a tea from peppermint leaves recovers about 20 – 25% of the volatile oil after 10 minutes steeping (Witchl, 2004). Decoctions involve soaking woody and root material in water to extract mineral salts and bitters in water. Plant matter can also be soaked in a carrier oil such as sweet almond in an oil type infusion. In this method, oil based constituents will be extracted, but not all water soluble constituents will make it into the infusion.
Tinctures: A tincture is made by soaking herb material in alcohol, vinegar, or vegetable glycerin, which acts as the solvent to extract the healing constituents. This method typically is preferable over water (or oil) extraction because it can dissolve both water and oil soluble substances and can be stored for a much longer period of time. With this method, it is important to understand the drug to extract ratio based on the solvent. Plus, the type of solvent used will extract differing percentages of constituents; a low alcohol content vodka that has more water added may get more hydrophilic constituents, were as with a high alcohol content vodka, more lipophilic components will also be extracted. Concentration of the extraction solvent is also important and affects strength (amount of active constituents) of a tincture (Witchl, 2004). Further, a fluid extract, where alcohol has been evaporated out of a tincture, will be a more concentrated herb preparation than a tincture. An example of herb preparations having differing strengths is a ginger tincture has a 1:5 drug to extract ration in alcohol and a 7:3 drug to extract ration in water (Witchl, 2004).
Steam Distillation of an Essential Oil: Steam distillation is a method of extracting just the essential oils from a plant. Steam distillation only extracts compounds with a maximum molecular weight of 225 – 250 (Clarke, 2002). Thus, the essential oil from a plant will have a significantly different chemical composition than an herb preparation of a plant because only the volatile chemical constituents are extracted. Typically, this represents 2% or less of a plant’s total matter. In reviewing a percent yield guide from The Essential Oil Company (2016), the percent yield for basil is 0.5 – 1.5%, cedarwood is 4.5%, eucalyptus is 1.0 – 7.0%, and rose petals are 0.006%. According to Clarke (2002), it would take about 4000 pounds of rose petals to produce 1 pound of essential oil! Thus, essential oils only contain the light weight chemical constituents, including terpenes (monoterpenes, sesquiterpenes, and sometimes diterpenes) and oxygenated compounds: alcohols, aldehydes, ketones, acids, esters, phenols, ethers, lactones, and oxides.
Further, some chemistry can change with the distillation process, when constituents become hydrolyzed by the hot water. An example is the linalyl acetate ester in lavender breaking down into linalool and acetic acid (Clarke, 2002). Another example: during steam distillation, the matricin component in German chamomile decomposes to chamazulene (Clarke, 2002). Essential oils are made up of multiple chemical constituents, and the quantity of each constituent can vary based on the quality and chemotype of plant matter used, conditions associated with the distillation process, and possible dilution and adulterations made to an oil.
When using essential oils, there tends to be a much smaller therapeutic margin than when using the whole herb, and it is important to be aware of key constituents in each oil, thus knowing the therapeutic benefits and also possible toxicity and contraindications. In addition, when making recipes and using oils, realize that all essential oils are volatile, meaning they evaporate easily, and are hydrophobic, meaning they are fat soluble; so they dissolve easily into oil based ingredients, and not well in water based ingredients. Below is a list of the general safety concerns by chemistry functional group of essential oils (Bowles, 2003):
With the concentrated and potent nature of essential oils, it is important to heed expert recommendations on their safe use. The National Association for Holistic Aromatherapy (2017) indicates some of the following guidelines with the use of essential oils at the safety tab of their website:
Examples of Chemical Differences: Peppermint, Ginger, and Anise
The following is a closer look at the therapeutic use of peppermint, ginger, and anise. It will look at a comparison of the difference between using a fresh herb, a dried herb, or an essential oil; including chemical components, appropriate methods of preparation, safe use, and Appendixes for each herb/essential oil on researched therapeutic actions.
Peppermint (mentha piperita) is an herb of the Lamiaceae family, known for its minty aroma and taste via its menthol essential oil constituent. The USDA (2016) report on fresh peppermint indicated it was 79% water, 15% carbohydrates ( including 8% fiber), 4% protein, and 1% fat. The dried herb showed a differing composition with less water: the USDA (2016) report for dried spearmint (dried peppermint was not available) indicated it was 52% carbohydrates, 20% protein, 11% water, and 6% fat. As it relates to the FDA (2015), based on the percent daily value for a 2000 calorie diet, a serving size of 2 Tablespoons of fresh leaves contains 2 calories, 1% of needed potassium for the day, 1% of dietary fiber, 1% of calcium, 2% of Vitamin C, 1% of iron, and 1% of magnesium.
Peppermint essential oil is obtained from steam distillation of the leaves. Percentage yield of distilled essential oil 1.0 – 2.5% (The Essential Oil Company, 2016). Chemical make up, according to Lis-Balchin (2006) is as follows: up to 50% menthol, up to 32% menthone, up to 10% isomentione, up to 14% 1,8-cineole, and up to 3% limonene. ACHS course material (2015) suggests an adult dose of 2 drops up to three times a day. Doses of the menthol constituent over 1 g per kg of body weight could be lethal (Ulbricht, 2010). Enteric coated capsules with peppermint oil could cause irritation with diarrhea or achlorhydria (WebMD, n.d.). Peppermint oil is also a potential mucous membrane irritant (NAHA.org, n.d.). Further, it is suggested to avoid with pregnancy, heart disease, epilepsy, and to use topically in a 2% dilution and avoid with damaged or sensitive skin (ACHS, 2015).
Menthol and menthone are the active constituents in peppermint oil and the peppermint herb (Natural Standard, 2016). These two constituents make up the majority of the essential oil, but can also be utilized from various herb preparations. Making a peppermint leaf tea recovers about 20 – 25% of the volatile oil after 10 minutes steeping (Witchl, 2004). Since some of the essentials can be extracted in a tea, it seems advisable that the lay person use fresh or dried peppermint for internal use, and the essential oil can be taken internally with the instructions of a Doctor or expert. For external use, the essential oil can be diluted at 2% in a carrier oil, with a skin patch test advised prior to application. Tinctures, poultices, and other methods can be made to also use the herb externally. In a diffuser, peppermint essential oil would also have many benefits. Appendix 2 lists much of the research about the healing potential of peppermint, with many studies referring to its constituents of menthol and menthone.
Ginger (Zingiber officinale) of the Zingiberaceae family is known for the healing benefits of its rhizomes. The USDA (2016) report on fresh raw ginger root indicated it was 79% water, 18% carbohydrates ( including 2% fiber), 2% protein, and 0.75% fat; the report on dried ground ginger root indicated it was 72% carbohydrates, 9% protein, 10% water, and 4% fat. The FDA (2015) indicates, based on a percent daily value for a 2000 calorie diet, for a serving size of 11 grams of fresh ginger root, it will contain 9 calories, 1% of needed potassium for the day, 1% of dietary fiber, 1% of Vitamin C, 1% of iron, and 1% of magnesium. As for dried and ground ginger, a serving of 5.2 grams contains 17 calories, 2% of the needed potassium, 3% of the dietary fiber, 1% of the protein, 1% of the calcium, 6% of the iron, and 3% of the magnesium. The maximum daily dose of ginger powder, tablets, capsules or fresh ginger is up to 5 g a day by mouth and divided into smaller doses (Ulbricht, 2010). Natural Standard (2016) indicates oral doses above 5 grams per day increase potential side effects. Ginger can be a skin irritant topically (Natural Standard, 2016).
Steam distilled from the dried rhizome, ginger yields .5 – 4% essential oil (Wichtl, 2004). Major compounds of the oil include 29% alpha zingiberene, 14% beta bisabolene and alpha farnesene, 10% beta sesquiphellandrene,10% beta phellandrene, and 8% camphene (Lis-Balchin, 2006). Also included in much smaller amounts are: alpha pinene, neral, geranyl acetate, linalool, and borneol (Lis-Balchin, 2006). Constituents vary based on geography (Peterson, 2015). The Australian variety is higher in monoterpenes and alcohols, Vietnamese and Indian varieties are higher in geraniol, and Jamaican is another unique chemotype (Peterson, 2015). Further, fresh ginger has more curcumene (Peterson, 2015). The suggested adult internal dose of ginger essential oil is one drop up to three times a day (ACHS, 2015). Dilute with topical use. Below are some listed concerns with the use of ginger essential oil:
Fresh and dried ginger, as well as ginger essential oil have their benefits of use. An overall recommendation is that the prefered internal use is fresh or dried, not to exceed max dosage (5 g a day for fresh), unless guided by a Doctor or expert. Dilute the herb and essential oil with topical use to avoid irritation, utilizing a skin patch test before application. Appendix 3 discusses research on the healing benefits of ginger.
Aniseed, coming from Pimpinella anisum of the Apiaceae family, smells like licorice, attributed to the anethole constituent. The herb comes from the ripe seeds of the anise plant. The USDA (2016) report for anise seed (dried) indicated it was 50% carbohydrates, 18% protein, 10% water, and 16% fat. The FDA (2015), indicated based on a percent daily value for a 2000 calorie diet, for a serving size of 1 teaspoon or 2.1 grams of dried anise seed, it contains 7 calories, 1% of dietary fiber, 1% of protein, 1% of calcium, 1% of Vitamin C, and 4% of iron. While aniseed has been used as a folk remedy for centuries, Natural Standard (2016) indicates there is not scientific evidence to suggest the proper herbal dose of the herb.
Essential oil is steam distilled from the seed with a percentage yield of 1.5 – 4.0 % (The Essential Oil Company, 2016). Constituent make up is up to 95% trans-anethole with small amounts of estragole and anisaldehyde, and it is often adulterated with star anise (Lis-Balchin, 2006). Star anise oil comes from the dry ripe fruit of Illicium verum, and has a slightly different chemical make up. ACHS recommends an adult dose internally of one drop up to three times a day for a maximum of two weeks (2015). Appendix 4 discusses therapeutic activity of anise seed and below are some safety concerns to heed when using the essential oil:
In recent years, essential oil use has increased rapidly and home based healing remedies are often given without the knowledge of the chemical strength within the bottle. Many people have the misconception that: “if it comes from a plant it cannot hurt you.” Based on scientific research demonstrating adverse reactions, NAHA advises not to use essential oils internally without being properly trained. Further, neat topical use is not suggested. In addition, the idea of adding essential oil to water generally does not work related to the concept of solubility. Herbs can be safer for general use, but there have also been many documented reports of overuse to cause harm. With each herb or essential oil, there are guidelines for the best method of preparation, dosage, and safe use that need to be heeded. It is important that people educate themselves on the research based benefits and potential side effects of an herb or essential oil before using it in and on their bodies via home based recipes.
Herbs and essential oils offer significant healing both to the whole body and to treat specific symptoms. But just like medicine, they have chemical components that have therapeutic action, therapeutic margin, drug interactions, and potential side effects. Preparation method of plant matter affects the concentration and strength of these constituents, with essential oils being composed of highly condensed chemicals that can be unsafe if used improperly. Teas, infusions, tinctures, fluid extracts, and steam distilled oils all have very differing constituents, concentration, effectiveness, and safe use guidelines, and it is important to be educated on these concepts and review scientific research of specific herbs or essential oils being used, instead of just trusting the anecdotal claims from friends and the internet.
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