Short Note on Essential Oil and its Extraction

 

Essential oil

An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the oil of the plant from which they were extracted, such as oil of clove. An essential oil is "essential" in the sense that it contains the "essence of" the plant's fragrance. Essential oils are generally extracted by distillation, often by using steam. Other processes include expression, solvent extraction, absolute oil extraction, resin tapping, wax embedding, and cold pressing. [1]

Characteristics of essential oil

Ø Highly concentrated

Ø Volatile

Ø Alcohol soluble

Ø Mostly colourless

Ø Less viscous than oil

Ø Watery texture

Ø The plants lending essential oils have distinctive fragrance [3]

Ø Essential oils are nearly always rotational and have a high refractory index

Ø They are sparingly soluble in water

Ø Usually less dense than water

Ø Liquid at room temperature,

Ø Essential oils are aromatic chemical compounds. [2] etc

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 Uses and benefits of essential oil

Ø Health benefits of essential oils

ü Headaches and migraines

ü Stress and anxiety 

ü Sleep and insomnia

ü Reducing inflammation

ü Antibiotic and antimicrobial

Ø Essential oils have many uses outside of aromatherapy.

Ø Many people use them to scent their homes or freshen up things like laundry.

Ø They are also used as a natural scent in homemade cosmetics and high-quality natural products.

Ø Essential oils could provide a safe and environmentally friendly alternative to man-made mosquito repellents, such as DEET. [4] etc 

Extraction of essential oil

There are a variety of methods employed in extracting essential oils from aromatic plants, however, the process of distillation is the main method for extracting the aromatic parts of plants.

1. STEAM DISTILLATION

Steam Distillation is the most popular method used to extract and isolate essential oils from plants for use in natural products. This happens when the steam vaporizes the plant material’s volatile compounds, which eventually go through a condensation and collection process.

Steam distillation process

1.     A large container called a Still, which is usually made of stainless steel, containing the plant material has steam added to it.

2.  Through an inlet, steam is injected through the plant material containing the desired oils, releasing the plant’s aromatic molecules and turning them into vapor.

3. The vaporized plant compounds travel to the condensation flask or the Condenser. Here, two separate pipes make it possible for hot water to exit and for cold water to enter the Condenser. This makes the vapor cool back into liquid form.

4.  The aromatic liquid by-product drops from the Condenser and collects inside a receptacle underneath it, which is called a Separator. Because water and oil do not mix, the essential oil floats on top of the water. From here, it is siphoned off. (Some essential oils are heavier than water, such as clove essential oil, so they are found at the bottom of the Separator.) [5]

Figure 1: Steam distillation process

Figure 1: Steam distillation process

1. 2. SOLVENT EXTRACTION

This method employs food grade solvents like hexane and ethanol to isolate essential oils from plant material. It is best suited for plant materials that yield low amounts of essential oil, that are largely resinous, or that are delicate aromatics unable to withstand the pressure and distress of steam distillation. This method also produces a finer fragrance than any type of distillation method.

Through this process, the non-volatile plant material such as waxes and pigments, are also extracted and sometimes removed through other processes.

Once the plant material has been treated with the solvent, it produces a waxy aromatic compound called a "concrete." When this concrete substance is mixed with alcohol, the oil particles are released. The aforementioned chemicals used in the process then remain in the oil and the oil is used in perfumes by the perfume industry or for aromatherapy purposes.

Figure 2: Solvent extraction process

Figure 2: Solvent extraction process

Solvent Extraction encompasses the following methods: Hypercritical CO2 (Carbon Dioxide), Maceration, Enfleurage. [5]

1.    3. Carbon-di-oxide EXTRACTION

Essential oils derived from the supercritical CO2 extraction of herbs are similar to the oils produced through distillation in that they can be used in aromatherapy and natural perfumery.

Oils derived from steam distillation vary in their qualities depending on the temperatures, pressures, and length of time applied for the process. The CO2 extraction process might thus produce higher quality oils that have not been altered by the application of high heat, unlike the steam distillation process. In  CO2 extraction, none of the constituents of the oil are damaged by heat.

Thus, the difference between traditional distillation and supercritical extraction is that instead of heated water or steam, CO2  is used as a solvent in the latter method. The supercritical extraction process operates at temperatures between 95 to 100 degrees F whereas steam distillation operates at temperatures between 140 to 212 degrees F.

In steam distillation, the molecular composition of both the plant matter and the essential oil are changed due to the temperature applied. On the other hand, a   CO2 extract is closer in chemical composition to the original plant from which it is derived, as it contains a wider range of the plant’s constituents.

For example, CO2  Extraction of German Chamomile flowers yields a green extract, because the absence of heat means it was not altered from its natural state or “denatured.” The resulting extract is thus more similar in composition to the original flower than the distilled essential oils is.

CO2 extracts are usually thicker than their essential oil counterparts and often give off more of the aroma of the natural herb, spice, or plant than a distilled essential oil. CO2 extracts have been said to contain more plant constituents than the amount extracted from the same plant using steam distillation.

The CO2 extraction process

  • Pressurized carbon dioxide becomes liquid while remaining in a gaseous state, which means it is now "supercritical." In this state, it is pumped into a chamber filled with plant matter.
  • Because of the liquid properties of the gas, the  CO2  functions as a solvent on the natural plant matter, pulling the oils and other substances such as pigment and resin from the plant matter. The essential oil content then dissolves into the liquid O2 .
  • The CO2 is brought back to natural pressure and evaporates back into its gaseous state, while what is left is the resulting oil.
CO2 extraction process

Figure 3: CO2 extraction process

CO2 is colorless, odorless, and can be easily and completely removed by releasing the pressure in the extraction chamber. It is what we exhale and is needed by plants in order for them to thrive, which illustrates its harmlessness when employed in the extraction process. This absence of potentially harmful solvents CO2 extraction means neither the human body nor the environment is polluted. [5]

1.    4. MACERATION

Macerated oils are also referred to as infused oils. They are created when carrier oils are used as solvents to extract therapeutic properties from plant material. The benefit of a macerated oil above a distilled oil is that more of a plant’s essence is captured in the oil, because it captures heavier, larger plant molecules than the ones captured in the distillation process. This keeps the product closer to retaining more of the plant’s valuable offerings.

The ideal plant material to be infused will be harvested so that it is as dry as possible, as any plant moisture will cause the oil to become rancid and will encourage microbial growth. Adding 5% of Vitamin E oil or Wheatgerm oil (which is high in Vitamin E) will prevent rancidity.

Maceration process

1.     Plant material is finely cut, crushed, or ground into moderately coarse powder.

2.     Plant material is placed in a closed vessel.

3.     Solvent (Menstruum) is added.

4.     The mixture is allowed to stand for 1 week and is shaken occasionally.

5.     The liquid is strained.

6.     Solid residue (Marc) is pressed to recover any remaining liquid.

7.     Strained and expressed liquids are mixed.

8.     Liquids are clarified through filtration or subsidence.


Figure 4: Maceration process

Figure 4: Maceration process

When the maceration process is complete, the base oil will likely have changed color. The final maceration should be filtered of its plant material and poured into an airtight container to be stored in a cool, dry place for up to 12 months. A macerated oil will go cloudy or will smell bad when rancid.

5-10% of a macerated oil can be used as an ‘active botanical’ in a cosmetic formula. Used in a larger quantity, it can also replace a plain base oil. [5]

1.    5. ENFLEURAGE

Enfleurage is not commonly used today, but it is one of the oldest methods of essential oil extraction that implements the use of fat. By the end of this process, either vegetable fat or animal fat becomes infused with the flower’s fragrance compounds. The fats that are used are odorless and solid at room temperature. The enfleurage process can be done either “hot” or “cold.” In both instances, the fat that is saturated with fragrance is called "enfleurage pomade."

Cold enfleurage

1.     Highly purified and odorless vegetable or animal fat, usually lard or tallow, is spread out over glass plates in a frame called a chassis and is allowed to set.

2.     Fresh flower petals or fresh whole flowers are then placed on top of the layer of fat and pressed in. They are allowed to set for 1-3 days or for a couple of weeks depending on the flowers that are used. During this time, their scent seeps into the fat.

3.     The depleted petals are replaced and the process is repeated until the fat reaches the desired saturation.

4.     The final product is the enfleurage pomade: the fat and the fragrant oil. This is washed with alcohol to separate the botanical extract from the remaining fat, which is used to make soap. When the alcohol evaporates from this mixture, the “absolute” is what is left over. [5]

Hot enfleurage

1.    The only difference in this process is that the fats are heated.

Figure 5: Enfleurage

Figure 5: Enfleurage

 6. COLD-PRESS EXTRACTION

This method is also called Expression or Scarification and is used for citrus peels in particular.

1.  The whole fruit is placed in a device that mechanically pierces it to rupture the essential oil sacs, which are located on the underside of the rind. The essential oil and pigments run down into the device’s collection area.

2.    The whole fruit is pressed to squeeze out the juice and the oil.

3.   The oil and juice that are produced still contain solids from the fruits, such as the peel, and must be centrifuged to filter the solids from the liquids.

4.   The oil separates from the juice layer and is siphoned off into another receptacle. [5]

Figure 6: Cold press extraction process

Figure 6: Cold press extraction process

7. WATER DISTILLATION

Delicate flowers such as roses and orange blossoms would clump together when introduced to steam in the distillation process, so the most effective method of extraction in this situation is to submerge fragile plant material in pure boiling water instead. The water protects the extracted oil from overheating. The condensed liquids cool down and separate from each other. The remaining water, which can sometimes be fragrant, is referred to by several names including hydrolate, hydrosol, herbal water, essential water, floral water, or herbal distillate. [5] 

Figure 7: Water distillation process

Figure 7: Water distillation process

 8. WATER AND STEAM DISTILLATION

In this method that can be employed with herb and leaf material, the plant material is immersed in water in a Still to which heat is applied. Steam is fed into the main Still from outside. [5] 

Citronellal

Citronellal or rhodinal (C10H18O) is a monoterpenoid aldehyde, the main component in the mixture of terpenoid chemical compounds that give citronella essential oil its distinctive lemon scent.

Citronellal is a main isolate in distilled oils from the plants Cymbopogon, lemon-scented gum, and lemon-scented teatree. The (S)-(−)-enantiomer of citronellal makes up to 80% of the oil from kaffir lime leaves and is the compound responsible for its characteristic aroma. [6]

Figure 8: Structure of citronellal

Figure 8: Structure of citronellal

Use and benefits of citronellal

Citronella essential oil has been used for a variety of purposes, including:

Ø as an insect repellent

Ø as an antifungal agent

Ø to treat parasitic infections

Ø to promote wound healing

Ø to lift mood or fight fatigue

Ø Physiological effects of inhalation

Ø Weight loss

Ø in perfumes or as a flavor additive in food [7]

Ø Citronellal used in veterinary medicine mainly in dogs and cats against some external parasites (lice, fleas, flies, etc).

Ø It is also used against agricultural and household pests.

Geranial

The monoterpene aldehyde, geranial and neral, isolated from ethyl acetate extracts of D. kotschyi and D. subcapitatum as well as Trypanocidal activities. the presence of geranial and neral, as a well-known mixture named citral, could be responsible for activity of the essential oil of Nepeta cataria against T. cruzi. [8] Geranial is a pale yellow, water-insoluble, liquid aldehyde, C10H16O, having a strong lemon like odor.

Figure 9: Structure of geranial

Figure 9: Structure of geranial

Use and benefits of geranial

Ø Anti-flammatory

Ø Antifungul

Ø Immune system stimulation

Ø Used in chemotherapy

Ø Migraine [9] etc

 Nerol

Nerol is a monoterpenoid alcohol found in many essential oils such as lemongrass and hops. It was originally isolated from neroli oil, hence its name. Like geraniol, nerol has a sweet rose odor but it is considered to be fresher.

Nerol can be synthesized by pyrolysis of beta-pinene, which affords myrcene. Hydrochlorination of myrcene gives a series of isomeric chlorides, one of which converts to neryl acetate. [10] 

Figure 10: Structure of nerol

Figure 10: Structure of nerol

Use and benefits of nerol

From nerol we can have neroli essential oil which can be used as

Ø Fragrance in perfumes and scented products

Ø An ingredient in body lotions and cosmetics.

Ø It can also be used in aromatherapy. [11]

Neroli oil has benefits for conditions like - 

ü depression

ü anxiety

ü high blood pressure

ü seizures

ü menopausal symptoms [11]

References

2.  Essential Oils and Their Characteristics; M.C.T. Duarte, R.M.T. Duart, R.A.F. Rodrigues and M.V.N. Rodrigues

3.  Development of Biomass Based Hydrothermal Liquefaction System for Essential Oil Extraction; Imlisongla Aier; N.L. Panwar

5. UNTAPPING THE POWER OF NATURE: ESSENTIAL OIL EXTRACTION METHODS

8.     Studies in Natural Products Chemistry; Soodabeh Saeidnia, Ahmad Reza Gohari, in Studies in Natural Products Chemistry, 2012

9. Essential Oil Compounds, Esessential oils, geranial, medical benefits, January 4, 2019

11. https://www.healthline.com/health/neroli-oil#benefits

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