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Research Paper
Chemistry
E-ISSN No : 2454-9916 | Volume : 7 | Issue : 11 | Nov 2021
1 1 1,2 3 3
Sujata Sengupta | Shivani Singh | Sharda Mahilkar Sonkar | Anand Sonkar | Nandini Kapoor |
3 3 3
Garima Tomar | Shweta Gaur | Aditi Bajaj
1Department of Chemistry, Miranda House, University of Delhi, Delhi-110007, India.
2Department of Chemistry, Hindu College, University of Delhi, Delhi -110007, India.
3Department of Botany, Hans Raj College, University of Delhi, Delhi-110007, India
1International Education & Research Journal [IERJ]
INTRODUCTION:
The culture of fragrances can be traced back to the ancient past. The Egyptians,
Greeks, Chinese and Indians; all have voyaged deep into the art of aroma. Scents
including Jasmine, Rose and Sandalwood have been narrated in the Vedas, the
1
oldest manuscripts in Indian history. The word perfume originates from the
Latin word “per fumum” meaning “through smoke” and refers to substances that
2,3
emit and diffuse a pleasant and fragrant odour. Chemistry has always played a
th
major role in modern perfumery. Until the mid-19 century, the use of perfumes
was limited to wealthy. Most perfumes are an amalgam of natural ingredients,
mostly of plant origin, which together provides the unique scent. These odour
bearing substances were found in limited supply and techniques used for their iso-
lation were cumbersome, providing poor yields. However, with advances in mod-
ern synthetic organic chemistry, the industry at present has witnessed a real
boom. Today, perfumes are used everywhere- from cosmetics products, to soaps
and detergents and even in pharmaceutical formulations. Modern day perfum-
ery now depends on the use of mixtures of both natural essential oils along with
synthetic aromatic chemicals. A perfume consists of three basic components: the
solvent - primarily a mixture of ethanol and water; fixatives - natural or synthetic
substances used to stabilize the vapor pressure and enhance the overall odour;
4
and essential oils - a complex mixture of odour bearing compounds. The human
body processes the scent in two ways, either through the olfactory system (which
is directly connected to the brain) or/and by absorption of the essential oils
through the skin.
This review articles aims to provide a brief overview of the science of perfumery,
highlighting the role of essential oils as the major source of natural fragrances.
Development in methods of isolation and extraction (solvent extraction, distilla-
tion, enfleurage, use of supercritical CO ) of the odour bearing compounds is
2
briefly discussed, a key factor responsible for the growth and development of the
perfume industry.
PERFUMES:
Fragrances or perfumes play an ever-increasing role in the cosmetics industry.
The simple addition of a sweet and pleasant odor, significantly influences the
5
overall impact of the cosmetic product on the consumer. Perfumes are defined as
substances that emit and diffuse a pleasant fragrant odour. Typically, perfumes
are volatile liquids and is usually a mixture of the fragrance bearing compounds
(essential oils or the aroma containing compounds) mixed with fixatives and sol-
6,7
vents. Until the 19th century, perfumes were usually composed of natural aro-
matic oils (essential oils obtained from plants) but nowadays, are mostly mix-
tures of various synthetic “aroma” containing components, thanks to recent
advances in synthetic organic chemistry.
Essential oils are a complex and diverse group of volatile and aromatic com-
pounds produced by living organisms, primarily of plant origin. More than 4000
aromatic and medicinal plant species are known till date, providing oils which
are an important source of fragrance and flavouring chemicals used in perfum-
8
ery, food and pharmaceutical industries. Chemically, essential oils are mixtures
of several 'aromatic' or odour bearing compounds, including, terpenes,
terpenoids (allylic, mono-, bi-, or tricyclic mono- and sesquiterpenoids) and
other compounds such as phenylpropanoids, benzenoids, and low molecular
9
weight aliphatic hydrocarbons. Essential oils are readily soluble in organic sol-
vents such as alcohol and ether but insoluble in water. They are usually colourless
and volatile liquids at room temperature. Typically, essential oils are secondary
plant metabolites produced in specialized secretory tissues/glands of various
plants and certain animals. In addition to having a pleasant odour, essential oils
are known to play key roles in the plant's defence mechanism and various signal-
10 11
ling pathways. The oils may be isolated from varying parts of the plants. Lav-
ender, rose and chamomile essential oils are isolated from the flowers of the
respective plants, while lemongrass and peppermint oils are isolated from the
leaves. Sandalwood, one of the most expensive essential oil, is commonly iso-
lated from the bark of the sandalwood trees. A variety of methods exists for the
extraction of these essential oils, including chemical methods such as steam dis-
tillation and solvent extraction, or mechanical methods such as expression
(flower petals or fruit rinds/peels are physically crushed) and enfleurage (the
12
essential oil is trapped within fat layers). A few of the major essential oils most
commonly used in perfumes and cosmeceuticals are listed in Table1.
ABSTRACT
Human beings have always been fascinated with the chemistry of fragrances. Since the earliest of times, man has always been interested in imitating nature's pleasant
smells, to find methods to mask or augment their own body odour through the application of perfumes. Traditionally, perfumes comprise of a blend of natural
components which together affords the unique pleasant odour. Modern day perfumery is a fusion of art, science and technology, with chemistry as the central science.
Majority of the perfumes used today are based on the application of synthetic aroma bearing molecules made available by advances in synthetic organic chemistry.
However, with the recent revival in popularity of the use of natural ingredients in cosmeceuticals, this review aims to re-look the chemistry of essential oils and its role
as a natural source of fragrance. Development in methods of isolation and extraction of the natural odour bearing compounds are key factors responsible for the growth
and development of the perfume industry.
Copyright© 2021, IERJ. This open-access article is published under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License which permits Share (copy and redistribute the material in any
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THECHEMISTRYOFESSENTIALOILANDITSROLEAS
NATURALFRAGRANCESINPERFUMES
Table 1: List of major essential oils commonly used in perfumes and cosmeceuticals
S. No
Essential Oil
Major Method of Isolation
Plant Part Used for Isolation
Major Constituent
Uses
1.
Bitter Almond
Distillation
Kernels
Benzaldehyde
Flavouring
2.
Bay
Distillation
Leaves
Eugenol
3.
Cinnamon
Distillation
Bark
Cinnamaldehyde, Eugenol, Eugenol acetate
Used in Artificial flavouring
4.
Citronella
Distillation
Grass
Geraniol (60-90%), citronellal
Perfumery, Disinfectants
5.
Clove
Distillation
Bud
Eugenol (80-85%)
Dentistry, Flavouring
6.
Lemon
Expression
Peel
d-limonene (90%), citral (5%)
Flavouring
7.
Coriander
Distillation
Seeds
Linalool, pinene
Flavouring
8.
Sandalwood
Distillation
Wood
Santalols (90%)
Perfumery
9.
Rose
Distillation or solvent Extraction
Flower petals or buds
Geraniol, rose ketones,
Perfumery, flavouring
10.
Jasmine
Enfleurage
Flowers
Linalool, methylanthranilate
Perfumery
11.
Eucalyptus
Distillation
Leaves
cineale (70%) citronella, terpenes
Decongestant
12.
Lavender
flowers
Linalool
Perfumery
A vehicle, or the solvent, is needed to keep the odoriferous substance in solution.
A solution of the essential oil with the appropriate solvent is called a fragrance
2,3
extract. Generally, highly refined ethyl alcohol is the solvent of choice.
Depending on the final use of the product, solubility characteristics of the essen-
tial oil and cost considerations, a small amount of water may be added to the alco-
13
hol. Apart from its role as a solvent, the alcohol also contributes to the particular
4
'note' of the perfume- the various scent fractions of the fragrance. Fragrances,
particularly liquid based ones, can be objectively classified according to the vary-
14,15
ing ratio of the essential oil and the solvent (alcohol), highlighted in Table 2.
This classification essentially refers to the overall strength of the fragrance,
dependent upon how much alcohol and/or water has been added to the essential
oils. Parfum (generally the most concentrated form available) has nearly 15-30%
of the essential oil dissolved in alcohol. Any mixture with a lower proportion of
oil to alcohol is known as an Eau.
Table 2: Classification of fragrances based upon varying ratio of the
essential oil and the solvent(alcohol)
Fixative is term used for compounds that 'fix' and help the fragrance to last longer
on the skin. Chemically, fixatives are natural or synthetic substances used to
reduce the rate of evaporation of the overall perfume and improve the stability of
the essential oil and thereby increasingthe overall shelf life of the perfume and
2-4
help in the proper blending/integration of the aromas or scents. Common natu-
ral fixatives include gums and resinoids (benzoin, labdanum, myrrh, olibanum,
storax) and animal products (ambergris, musk and civet). Synthetic fixatives
include odorless solvents with low vapor pressures (benzyl benzoate, diethyl
phthalate, etc.) and substances of low volatility (benzyl salicylate, ambroxide,
16
etc.).
Composition of Essential Oils:
Essential oils are concentrated hydrophobic liquid containing volatile odorifer-
ous compounds derived from the different parts of the plants. A particular essen-
tial oil can be composed of several components in varying composition, with two
or three major components being present at high individual concentrations
(20–70%), compared with the other components which may be present in trace
30
amounts. The overall fragrance of the essential oil relies on the specific odour of
the individual components, which is determined by its structure and volatility.
According to their chemical structure, these odour bearing compounds can be
divided into four major groups: terpenes, terpenoids (allylic, mono-, bi-, or
tricyclic mono- and sesquiterpenoids ), pheny lpropanoids, and "other s"
31
(benzenoids, low molecular weight aliphatic hydrocarbons, etc.). Furthermore,
these components consists of diverse functional groups, ranging from hydrocar-
bons (monoterpenes, sesquiterpenes, and aliphatic hydrocarbons), oxygenated
compounds (monoterpene and sesquiterpene alcohols, aldehydes, ketones,
esters, and other oxygenated compounds); and sulphur and/or nitrogen contain-
32
ing compounds (thioesters, sulphides, isothiocyanates, nitriles, etc.).
Terpenes constitute the largest group of natural fragrances. Chemically, terpenes
are a class of hydrocarbons occurring widely in plants and certain animals. Their
classification is based on the number of isoprene (C H ) units present in their
5 8
structure - hemiterpenes (C ), monoterpenes (C ), sesquiterpenes (C ) and
5 10 15
2-4
diterpenes (C ). Monoterpenes (C H ), diterpenes and sesquiterpenes (C H )
20 10 16 15 24
are most abundant in the essential oils from plants. Common examples include
monoterpenes myrcene and limonene and sesquiterpenes -himachalene. Oxy-
genated derivatives of terpenes are commonly known as terpenoids and are
another major component of essential oils. Linalool, citronellal, citral (geraniol
and neral) are some of the major terpenoids widely abundant in essential oils and
extensively used in the perfume industry (see Figure 1). Esters of anthranilic
acid, salicylic acid and benzyl alcohol are example of benzenoids found as major
components of certain essential oils. Methyl anthranilate, amyl salicylate,
methyl salicylate and benzyl cinnamate are common examples. Eugenol,
anethole, and myristicin are examples of phenylpropanoids, another class of com-
pounds found in certain essential oils. Phenylpropanoids, also a class of second-
ary plant metabolites, are a diverse group of compounds derived from the carbon
skeleton of phenylalanine that are involved in plant defense, structural support,
33,34
and overall survival of the plant.
Figure 1: Structures of common components of essential oils
Various Methods of Isolation of Essential Oils:
“Aroma Extraction or fragrance extraction” commonly refers to the extraction of
the odoriferous “aromatic” compounds from raw materials using common meth-
17
ods such as distillation, solvent extraction or expression. The ultimate essence
obtained has many different terms -essential oil, concrete, absolute, etc. In gen-
eral, the major methods routinely used for the isolation of volatile oils from
plants include: expression, distillation, extraction with volatile organic solvents
and absorption in purified fats (enfleurage). Each method has their own distinct
set of advantages and drawbacks. The methods, though popular, may also prove
to be damaging- where the odoriferous compounds get denatured during the
extraction process due to heat, exposure to oxygen or chemical reaction with the
solvent. This may produce an extract with an aroma distinct from the aroma of
the raw materials or render them completely odourless.
Extraction with Volatile Solvents:
Solvents such as hexane, purified petroleum ether and ethanol are generally used
1
for the extraction of essential oils from the plant material by solvent extraction. It
is one of the most common and economically important technique of extraction
in the modern perfume industry. The raw materials are submerged and agitated in
the suitable solvent to allow dissolution of the odoriferous components. Criteria
for the selection of a suitable solvents include: high selectivity (the solvent
should be capable of dissolving only the odoriferous component), a low boiling
point (easy and complete evaporation of the solvent without leaving any residue
behind once the extraction is complete), chemical inertness to the odoriferous
Terpenes
Research Paper
E-ISSN No : 2454-9916 | Volume : 7 | Issue : 11 | Nov 2021
2 International Education & Research Journal [IERJ]
Fragrance Type
% Essential Oil
% Alcohol
Perfume (Perfum)
15-30
90-95
Eau de Toilette
4-8
80-90
Eau de Parfum
8-15
80-90
Cologne Splas
1-3
80
Eau de Cologne
3-5
70
Alcohols
Aldehydes/Ketones
Benzenoids
Phenylpropanoids
Components from
animals
components, cheap and inflammable. A typical solvent extraction method first
involves treatment/agitation of the plant material with a suitable organic solvent.
The desired aroma containing compounds dissolve, after which the solution of
the aromatic substances is evaporated to produce a “oleoresin or concrete" (a
waxy semi-solid residue containing the essential oil, waxes and resins). The con-
crete is often mixed with alcohols to remove the unwanted waxes and resins. The
alcohol is then removed by a second distillation, leaving behind the pure essen-
1,2
tial oil called the “absolute”. Extracts from plants such as jasmine and rose, are
called absolutes. The solvent used during the extraction process is usually con-
densed, rectified and reused for a second batch. Though the method is used to
extract essential oils from plants, it is best suited for those oils isolated from ani-
mal secretory glands, such as civet and ambergris. It produces a finer fragrance as
18
compared to any type of distillation method.
Expression:
Expression is one of the most traditional yet common method for the extraction
of essential oils. Expression, also termed as "expeller-pressed" or “sponge pro-
cess” involves the pressing, squeezing or compression of the raw plant materials
1,2
to extract the essential oil. Since no heat is required during the extraction pro-
cess, it's also known as “cold-pressed” method. Today, the method is most com-
monly used for the extraction of essential oils obtained from peels of fruits of the
18
citrus family. Traditionally, the citrus fruit peels were soaked in water after
which the peels would be pressed against a sponge. Once the sponge is saturated
with the oil, it is hand squeezed to release the essential oil. Modern expression
now involves mechanical or cold pressed techniques. The pelatrice and
sfumatrice processes are most popular mechanical processes for citrus oil isola-
19
tion in Italy. In the simplest mechanical method, the entire fruit is placed in an
expression machinery where it first pricks the surface of the peel. As this process
occurs, small sacs containing the essential oil break open and releases the oil.
Water is then sprayed over the fruit to collect the essential oil. At this stage how-
ever, the essential oil may be mixed along with some additional watery materials
from the fruit's flesh. To isolate the essential oil, the mixture is either filtered and
centrifuged to separate out the pure essential oil product or the oil is forced out
from the material under high mechanical pressure. Expression usually provides a
high quality of the final product with characteristic fragrances identical to the
starting raw materials. This method is especially beneficial for extraction of
those essential oils that lose their fragrance when exposed to high temperatures in
methods like steam distillation.
Distillation:
Distillation is the most popular method used to extract essential oils from plant
materials. The process is particularly used for obtaining essential oils present in
1,2
cumin, anise, lavender, rose, fennel, mace, and nut meg. This method involves
heating the volatile essential oils to their vapor state followed by condensation
into the liquid state. There are various distillation techniques employed to obtain
essential oils: water or hydro-distillation, steam distillation and hydro-diffusion,
of which steam distillation is most widely accepted method on a commercial
18
scale. In this method, the plant materials are charged into large distillation con-
tainers called “stills” (nearly 600-gallon capacity tanks made of tin with a copper
lining). Steam is injected through an inlet and distillation is carried out. The
steam releases the essential oil from the plant feed, after which, it passes through
a cooling system with a condenser, where the vapor mixture is cooled and col-
lected in a 'separator'. The essential oil separates from the distillate and may be
collected. Since the temperature never goes above 100 °C during the distillation
process, heat and temperature sensitive essential oils may be easily extracted by
20,21
steam distillation. In the hydro-distillation technique, the plant material is
completely submerged in sufficient quantity of water, and brought to a boil by
applying direct heat. The essential oil distils out, along with water and then is sep-
arated after condensation. Water distillation is the most common method of dis-
tillation primarily due to the low costs involved. However, steam distillation
boasts of a higher efficiency and a higher quality of essential oil extraction com-
pared to water distillation, since the water and the plant feed are not directly in
contact with each other.
Enfleurage:
Enfleurage is one of the oldest methods of extraction of essential oil from flowers
1,2
with the use of fats. However, with modern methods of extraction such as distil-
lation and solvent extraction, it has lost its popularity. The fats used in this
method are odorless and solid at room temperature. Once the fat is infused with
the fragrance, it is referred to as "enfleurage pomade". Depending on whether
heat is applied during the extraction process, enfleurage is of two kinds: hot or
18
cold.
In cold enfleurage method, a large framed plate of glass, the 'chassis' is smeared
with a layer of the highly purified fat (usually animal fat such as lard) and allowed
to set. Fresh plant raw material (flowers or petals) is placed on top of the layer of
fat and are allowed to set for few days, to allow the scent to diffuse into the fat.
The process is repeated with fresh plant feed till the fat reaches the desired satura-
tion. The final product (the fat saturated with the fragrant oil) may either be used
as is or the oils are captured by dissolving the fat in an alcoholic solvent. The alco-
hol evaporates from this mixture to leave behind the pure "absolute" essential oil.
In hot enfleurage, a similar protocol is followed but the only difference being that
1
the ingredients are stirred in hot animal fat until desired oil is obtained.
Enfleurage has certain drawbacks: the concentration of the odiferous oil is usu-
ally low, the fats are not a pleasant material to handle and often turns rancid after
repeated use.
Innovative Techniques for Green Extraction:
Supercritical Fluid Extraction:
With increased interest in cleaner and greener methods of separation techniques,
supercritical fluid extraction has gained much popularity in the food and flavour-
22
ing industry, especially for the decaffeination of coffee and tea. Supercritical flu-
ids, above their critical points, exhibit properties characteristic of both liquids
(high solvating power) and gases (high diffusivity and low viscosity). Solvents
like CO , butane and ethylene are now commonly used in their supercritical
2
states for various industrial applications. CO , in particular, is the supercritical
2
solvent of choice, since it is an odourless, colourless, non-toxic, non-flammable
and recyclable gas, whose supercritical state is reached at relatively low pres-
sures and near room temperature (T = 31.2 ᵒC and T = 7.3MPa). Not only does it
c p
behave as a lipophilic solvent, its solvating power may be tweaked as par require-
23
ment. SFE, has also been explored for the extraction of fragrances from plant
materials. Conventional extraction techniques, such a solvent extraction and dis-
tillation, though extensively used, have several drawbacks: low selectivity, high
energy requirements and a possible loss of the volatile essential components.
Extraction of essential oils with supercritical CO , therefore, provides an attrac-
2
tive and green approach for the isolation of fragrances, especially for eucalyptus
24,25
and lavender oil.
1,18,26
SFE with CO typically involves a semi-continuous batch process. The
2
extraction vessel is charged with the dried and finely powdered plant feed, after
which, the supercritical solvent is continuously loaded from the bottom of the ves-
sel. The supercritical fluid along with the extracted plant extracts then exit the ves-
sel through a depressurization valve into a separator. Due to low pressure, the
extracted essential oils separate from the gaseous CO solvent and are collected.
2
The gaseous solvent is usually recycled back into the system. Lavender essential
oil, may be extracted from Lavandin (L. hybrida) flowers with SFE using the fol-
lowing conditions: temperature at 90.6 °C, pressure at 6.3 MPa and solvent flow
−1
rate of 0.2 mL min to provide separation of the odoriferous constituents of 1,8-
creole, linalool, linalyl acetate and camphor, which is commonly used by the
27
food and fragrance industries.
Microwave-Assisted Extraction (MAE):
Conventional extraction processes usually require the use of massive energy. In
order to reduce this energy consumption, one can assist existing processes with
intensification technologies to produce high-quality innovative fragrance
extracts. Activation technologies, particularly microwaves, enable the develop-
ment of solvent-free industrial processes, an even more advantageous and
28
greener alternative.
Microwave-assisted extraction (MAE) is a relatively new extraction technique,
combining the power and principles of microwaves with traditional solvent
extraction. The solvents along with plant tissues, containing the natural prod-
ucts, are heated during the extraction with microwaves. MAE has several advan-
tages over traditional extraction techniques: higher extraction rates, shorter
extraction time, use of less amounts of solvents, and lower costs. The use of MAE
for the isolation/extraction of essential oils has gained much popularity in recent
times pres-
29
. Several modified versions of MAE methodologies exist, including
surized microwave-assisted extraction (PMAE) and solvent-free microwave-
assisted extraction (SFMAE). In SFMAE, the plant feed is placed in the micro-
18
wave reactor without the addition of any solvent (water or organic solvents).
The microwave expositions result in the heating of the internal water of the plant
matrix, rupturing the glands and releasing the volatile essential oils, which get
evaporated. The vapours are then cooled and condensed in a cooling system
located outside the microwave and collected in special glassware. The excess
water may be refluxed and recycled back to the extraction vessel. Furthermore,
the extracts are obtained in high yields and are free from any contaminants.
Because of the shortened extraction times, this method is environmentally
friendly. However, essential oils containing odoriferous components composed
of low boiling point hydrocarbons do tend to undergo decomposition.
Major Essential Oils in India:
India is currently one of the world's largest producer and exporter of essential oils
35
and their value-added products. Boasting of a rich biodiversity, large scientific
manpower and modern industrial set up, the essential oil cultivation and process-
ing has seen tremendous growth over the years. Many aromatic plants have been
introduced and successfully cultivated in India (menthol, lemongrass, citronella
etc.).A few of the major essential oils produced in India are highlighted below.
Rose Oil:
Rose oil, also known as rose otto or attar of rose or rose absolute, is the most
widely used essential oil in perfumery and cosmetics. Two major species of roses
are cultivated for the production of rose oil- Rosa damascena (or damask rose,
found in India, Turkey, Bulgaria, etc.) and Rosa centifolia (found mostly in Egypt
and France). The production of rose oil is a labour-intensive process, especially
due to the low content of the oil in rose blooms (0.03-0.04%). The oil is extracted
from the rose bud and petals, where nearly 3.5 tons of rose petals produce only 1
36
kg of rose otto.
3International Education & Research Journal [IERJ]
Research Paper
E-ISSN No : 2454-9916 | Volume : 7 | Issue : 11 | Nov 2021
Components:
The chemical composition of rose oil is quite complex and consists of more than
300 known compounds. The most common chemical components present in the
rose oil are - citronellol, phenyl ethyl alcohol, geraniol, neral, nonadecane and far-
nesol along with traces of linalool, nonanal, phenyl acetaldehyde, citral, carvone,
eugenol and rose oxides.The major components of rose water volatiles obtained
from the bud and full bloom stages of Rosa damascena Mill. from cultivar
'Ranisahiba' in Uttarakhand, India was phenyl ethyl alcohol (66.2–79.0%),
37,38
geraniol (3.3–6.6%) and citronellol (1.8–5.5%).
Method of Extraction:
The main industrial products are rose oil, rose water, rose concrete and rose abso-
lute, all of which are produced by hydro-distillation and solvent extraction pro-
cesses. Rose otto essential oil (or Attar of Rose) is a product isolated during steam
distillation and is a light-yellow aromatic liquid (crystallizes at low tempera-
tures) and is used widely in the fragrance and food flavouring industry. In the dis-
tillation method, fresh rose blooms (picked before sunrise) are agitated along
with water in large stills or vats and steam-heated. The vapours containing the
rose oil then enters the condensing chamber, are condensed and separated to col-
lect the concentrated rose oil, also known as “direct oil”. The water-soluble por-
tions are repeatedly distilled to obtain the “indirect oil”. The direct and indirect
rose oils are combined and afford the final rose oil (Rose Otto or Attar). The
hydrosol portion of the distillate, commonly known as rose water, is an inexpen-
sive by-product widely used in food flavouring and skin care products. Rose Otto
has a more delicate aroma and expensive as yields are generally low.
Rose Absolute is the aromatic oil obtained from the fresh petals of the Damask
Rose (Rosa damascena) by solvent extraction. Highly popular in the perfume
industry, rose absolute is a viscous, golden amber coloured concentrated oil with
a strong and intense rose odour. In the solvent extraction method, the fresh rose
blooms are agitated in large vats with an organic solvent, usually hexane, which
draws out the aromatic compounds along with other soluble substances such as
waxes and pigments, as well. The extract is then subjected to a vacuum procedure
that removes the solvent for re-use. The waxy mass which remains is termed con-
crete. The rose concrete is agitated with alcohol at low temperatures (-15 °C to -
20 °C) due to which the aroma containing components dissolve, leaving behind
the wax impurities. The alcohol is evaporated under low-pressure conditions and
rose absolute is obtained as the final product. Rose Absolute is extremely con-
centrated and reflects more of the true 'Rose' odour compared to rose otto.
Uses:
Rose oil is a common component in a variety of cosmetic products, such as soaps,
powders, creams, etc. Rose oil has various anti-inflammatory and nourishing
properties as well. It helps in healing and protecting the surface of the skin, thus
providing a youthful complexion. It's known to possess antidepressant and there-
fore is commonly used in aromatherapy to help soothe the mind. Rose oil is also
known to possess antiseptic and antiviral properties.
Sandalwood Oil:
Sandalwood oil is the essential oil obtained by steam distillation of the chips of
the heartwood of various species of the sandalwood trees of the Santalum spe-
cies, Santalum album (Indian Sandalwood) and Santalum spicatum (Australian
sandalwood).
Components:
Sandalwood oil comprises of more than 90% sesquiterpene alcohols, α-santalol
(50-60%) and β-santalol (20-25%), responsible for the pleasant and characteris-
39,40
tic aroma of the oil. S. album heartwood is known to contain the highest con-
centration of the oil and the highest proportion of the santalols. The composition
and oil content depends on the species, region grown, age of tree, the season of
41
harvest and the extraction process used.
Method of Extraction:
Hydro-distillation is the conventional method of extracting sandalwood essen-
tial oil. The powdered wood is soaked in water and boiled over an open fire. The
oil floats to the surface, above the hydrosol, and collected. However, the process
is time consuming and requires heating a huge quantity of water, raising the cost.
Furthermore, the heat often "burns" the oil, making its quality poor. Modern
methods of sandalwood oil extraction involve steam distillation and supercritical
CO extraction. In steam distillation, super-heated steam is passed through the
2
powdered heartwood after which the steam rich in sandalwood oil is cooled to
obtain the sandalwood hydrosol and sandalwood essential oil. Typically steam
distillation yields 3.6% of oil after 24 h of distillation. Recently, sandalwood has
been extracted with subcritical CO (at 200 bars and 28 °C), proving to be more
2
efficient than steam distillation, providing a yield of 4.11% of the oil in the first
42
hour.
Uses:
Sandalwood oil is an excellent, mild and long-lasting sweet fragrance used
widely in perfumes and cosmetic products. It also serves as an excellent base and
fixative for other high-grade perfumes. In addition, sandalwood has antipyretic,
antiseptic and diuretic properties and has been used in Ayurvedic medicine for
43
the treatment of headaches, stomachache, and urinary tract infections.
Peppermint Oil:
Peppermint (Mentha piperita L.) is a perennial aromatic herb belonging to the
Lamiacae family, native to the Mediterranean regions, but now cultivated all
over the world. Peppermint is one of the most useful medicinal and aromatic
plants. Members of this mint family are characterized by their volatile oils, pep-
permint essential oil, used widely by the flavoring, perfume and pharmaceutical
44
industries.
Components:
The most abundant odoriferous chemical compounds isolated from peppermint
essential oils are oxygenated monoterpenes (72.34–86.41%), particularly, men-
thol (30-50%), a monoterpene alcohol, primarily responsible for the strong
45
minty, cooling odour and taste characteristic to the oil. Other major constituents
of the oil include menthone, 1,8-cineole, neo-menthol and the carboxyl esters,
menthyl acetate in particular. Peppermint oil also contains traces of terpenes such
as limonene, pulegone, caryophyllene and pinene. The chemical composition of
peppermint leaves may vary with plant maturity, geographical region, and pro-
46
cessing conditions.
Extraction:
Peppermint oil is extracted by three methods: solvent extraction, Soxhlet and
47
steam distillation. The isolation of peppermint oil by solvent extraction
involves mixing the fresh and dry peppermint leaves with an organic solvent,
ethyl alcohol, for several hours at slightly elevated temperatures. The solvent is
then evaporated off to recover the oil. Steam distillation uses heat from steam or
water to break the oil glands in peppermint leaves and vaporizes the oil, which is
then condensed and separated from water. In the Soxhlet extraction, fresh and
dry peppermint leaves are placed in the thimble of the Soxhlet apparatus, which
is placed in a distillation flask, usually containing the solvent, hexane. After
repeated extraction cycles, the desired peppermint oil concentrates in the distilla-
tion flask. After which, with the help of a rotary evaporator, the solvent is
48
removed to yield the extracted oil.
Uses:
Peppermint oil is extensively used in the food flavouring, perfumery and phar-
maceutical industry. The oil adds a fresh, pleasing fragrance to soaps and other
cosmetic products. It is also used as a flavouring agent in foods and in products
such as mouthwashes. It is helpful in the treatment of irritable bowel syndrome
(IBS), nausea, various digestive issues, as well as the common cold and head-
49
aches.
Lemongrass Oil:
Lemon grass (Cymbopogon citratus), belonging to the Poaceae family, is a
perennial grass with thin, long leaves and cultivated in tropical countries, espe-
50
cially in Southeast Asia. This plant species is one of the main sources of
lemongrass essential oil, generating nearly 1000 tons of the oil annually. The
Lemongrass essential oil is extracted from the leaves of the plant and is widely
used in the pharmaceutical, flavoring, perfumery/cosmetics, and agriculture
51
industries. The oil possesses a refreshing and calming aroma, leading to a plea-
52
surable sensation. Recent scientific studies have indicated lemongrass essential
oil possess antioxidant, antimicrobial, antifungal, anti-inflammatory and
anticancer activities.
Components:
The major odoriferous components present in lemongrass essential oil are
terpenes limonene, β-myrcene, citral, geraniol, citronellol, neral and geranyl ace-
tate. Limonene and β-myrcene are mostly responsible for the distinct odor char-
acteristic to lemongrass. However, citral, is the predominant component of
lemongrass essential oil. Citral is a mixture of two isomeric terpenoids
(monoterpene aldehydes), neral, the cis isomer (25% to 38%) and geranial, the
predominant trans isomer (40-62%) In general, the chemical composition of
lemongrass oil varies, depending upon the habitat, growth conditions, the time of
53
year the plant is harvested and extraction techniques used. Furthermore, the
quantity of citral present in lemongrass oil determines its quality, the higher the
54
content of citral, higher the purity of the essential oil.
Method of Extraction:
Lemongrass essential oil may be extracted by several different methods such as
solvent extraction, steam or hydro distillation, and supercritical fluid extraction
55-57
(SFE) using CO . Isolation by solvent extraction involves mixing the plant
2
material with an organic hydrocarbon, usually n-hexane, to dissolve the essential
oil. Filtration followed by concentration by distillation to remove the solvent,
leaves behind the essential oil. The method is efficient and simple; however,
large volumes of the organic solvent is required and contamination of the essen-
tial oil with the solvent is common. The Soxhlet apparatus is also commonly used
58
for solvent extraction of lemongrass essential oil. The most popular method for
the isolation of lemongrass oil is by steam and hydro distillation. In steam distil-
lation, the steam passes through fresh or wilted lemongrass leaves, softening the
cells to allow the essential oil to escape and vaporize. Subsequently, the steam
and vapors of the oil are cooled in a condenser, separated and collected. Yields of
lemongrass oil obtained by steam distillation ranges from 0.24% to 0.71%.
Hydro-distillation of lemongrass is usually performed using a Clevenger-type
apparatus where the lemongrass leaves are completely immersed in water and dis-
59
tilled upon heating. The method is simple, cost effective and yields of the oil are
4 International Education & Research Journal [IERJ]
Research Paper
E-ISSN No : 2454-9916 | Volume : 7 | Issue : 11 | Nov 2021
better (up to 1.80%). Modern methods of extraction involving microwave-
assisted hydro-distillation and subcritical carbon dioxide extraction, are reported
and promising, though the methods are expensive and yields are not significantly
57
any better.
CONCLUSION:
The chemistry of essential oils and its role in perfumes has always fascinated
mankind. Modern day perfumery is mostly based on the application of synthetic
aroma bearing molecules, made available by advances in synthetic organic chem-
istry. However, the use of essential oils from natural sources has seen a recent
revival in its popularity. Its ability to impart a wide range of aroma along with
medicinal properties has made them highly valued ingredients in perfumes and
cosmeceuticals. Hydro- and steam distillation and solvent extraction are the pre-
ferred methods of extraction of essential oils for a very long time. Recent
advances and innovation in cleaner, greener and more energy efficient extraction
technologies, such as SFE and MAE, now provides a sustainable approach to the
extraction of the natural ingredients. However, there is still a long way to go to
before these techniques can become feasible alternatives to conventional meth-
ods.
Declarations:
Author contribution statement:
All authors listed have significantly contributed to the development and the writ-
ing of this review article.
Acknowledgement:
The present work has been carried out as part of an online summer research
internship programme titled “Flavours of Research”, part of the D S Kothari Cen-
tre for Research and Innovation in Science Education, Miranda House, Univer-
sity of Delhi, funded by the Department of Science and Technology, Government
of India. We are thankful to the Principal, Miranda House, for the permission and
encouragement, to pursue the present study.
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