VOLATILE OILS
 Volatile or essential oils are volatile in steam.
 They differ entirely in both chemical and physical
properties from fixed oils.
 They are secreted in:
oil cells e.g. Cinnamon
Oil glands e.g. Clove
Secretion ducts (vittae) e.g. Anise
Glandular hairs e. g. Chamomile
 They are frequently associated with other substances
such as gums ( oleo gum) and resins (oleoresin) or both
(oleo gum resin)
Production and Uses of Volatile Oils
There are about 100 commercially valuable volatile oils
directly derived from plants.
 Volatile oils are used:
1- For their therapeutic action: antiseptic e.g. thyme and
clove, carminative e.g. Mentha
2- Flavoring (e.g. oil of lemon),
3- in perfumery (e.g. oil of rose)
4- starting materials for the synthesis of other compounds
(e.g. oil of turpentine).
 For therapeutic purposes they are administered as
inhalations (e.g. eucalyptus oil), orally (e.g.
peppermint oil), as gargles and mouthwashes (e.g.
thymol) and transdermally (many essential oils
including those of lavender, rosemary and bergamot
are employed in the practice of aromatherapy).
 Those oils with a high phenol content, e.g. clove and
thyme have antiseptic properties, whereas others are
used as carminatives.
 Oils showing antispasmodic activity, and much used in
popular medicine. e.g. fennel, mentha, caraway,
chamomile, anise, rosemary.
Composition of Volatile Oils
 Volatile oils are generally mixtures of
hydrocarbons and oxygenated compounds
derived from these hydrocarbons.
 The odour and taste of volatile oils is mainly
determined by these oxygenated constituents,
which are to some extent soluble in water but
more soluble in alcohol.
 Practically all volatile oils consist of chemical mixtures
that are often quite complex; they vary widely in
chemical composition.
 Almost any type of organic compound may be found in
volatile oils (hydrocarbons, alcohols, ketones,
aldehydes, ethers, oxides, esters, and others).
 It is not uncommon for a volatile oil to contain over 200
components, and often the trace constituents are
essential to the odor and flavor. The absence of even
one component may change the aroma.
Determination of the structure of terpenes
Chemical constituents of volatile oils may be divided
into 2 broad classes based on their biosynthetic origin:
1- Aromatic compounds formed via shikimic acid. These contain C6
phenyl ring with an attached C3 propane side chain.
2- Terpene derivatives formed via acetate mevalonic pathway.
Classification of constituents of volatile oil:
1- Hydrocarbons
- Unsaturated acyclic hydrocarbon eg. myrcene
-Aromatic hydrocarbon eg. p-cymene
Monocyclic eg. limonene which occur in citrus fruit,
mint, thyme.
Bicyclic eg. α-pinene found in lemon, anise, eucalyptus,
thyme, fennel.
* Limonene and α-pinene are biosynthesised from terpene pathway.
- Sesquiterpene eg. Chamazulene
2- Alcohols:
-Eg. Linalool, Citronellol
Aromatic alcohol eg. benzyl alcohol
3- Ketones:
Camphor occurs in rosemary, lavender.
Uses: topical antipruritic, rubefacient, anti-infective.
Rosemary
Lavender
4- Esters:
-Methyl salicylate
* Methyl salicylate also this oil is known as wintergreen oil.
Uses: methyl salicylate has local irritant, antiseptic,
antirheumatic properties.
5- Phenols:
CH3
OH
H3C
CH3
Thymol
Eugenol, Thymol are the most important phenol present in volatile
oil.
Eugenol occur in clove oil and in cinnamon bark.
Uses: as dental analgesic, antiseptic,
counter irritant, carminative.
Eugenia caryophyllus
CH3
Thymol occurs in Thyme oil.
OH
Uses: antifungal, antibacterial agent.
H3C
CH3
Thymol
Phenolic ether volatile oil
Safrole from myristica or nutmeg
uses: flavoring agent and carminative.
Physical Properties
Although volatile oils differ greatly in their chemical constitution,
they have a number of physical properties in common:
1.
They possess characteristic odors.
2.
They are characterized by high refractive indices.
3.
Most of them are optically active.
4.
Their density is generally lower than that of water (the
essential oils of sassafras, clove, or cinnamon are the
exceptions).
5.
As a rule, volatile oils are immiscible with water, but they are
sufficiently soluble to impart their odor to water. The
aromatic waters are dependent on this slight solubility.
Preparation of volatile oils
1.
2.
3.
4.
5.
The principal methods used in the preparation of
volatile oils from plants depend on:
Distillation in water or steam.
Scarification and expression.
Extraction with solvents.
Enzymatic hydrolysis (for glycosidic volatile oils e.g.
mustard oil).
Enfleurage (extraction of oils used in perfumery).
I- Distillation Methods:
• There are two types of traps:
One for oils lighter than water and the other for oils heavier
than water.
• These two types differ only in the mechanism of the return
of the aqueous layer to the distillation flask, keeping the
volatile oil layer in its position.
Types of distillation used:
1-Water and steam distillation
2-Direct steam distillation
Clevenger apparatus for
volatile oil preparation
Points for consideration in the distillation method:
1- It is often necessary to subject the plant material to special
treatment prior to steam distillation e.g. cut or crushed.
Crushing or cutting facilitates penetration of water into
oil- containing structures in the plant.
eg. Oil cells, glandular hairs.
2- For removal of water or moisture which might be present in
the prepared volatile oil, anhydrous sodium sulfate is usually
used.
Some volatile oil can´t be distilled without
decomposition and are usually obtained by:
II- Expression method
Expression can be carried out by means of any of
the following three processes:
a) Sponge method:
- The citrus fruit (orange, lemon) is washed, cut into
halve and the juicy part removed.
- The rind is squeezed, when secretion glands rupture
and the oil collected by mean of the sponge, until the
sponge becomes saturated with water and oil.
- The sponge is then periodically squeezed in a vessel.
- The upper oily layer in the vessel is separated.
b) Scarification method:
- Citrus oil involve puncturing the oil glands by rolling the fruit over
a trough lined with sharp projection that are long enough to penetrate
the epidermis.
- By repeatedly rotating the instrument after placing lemons in the
bowel the oil glands are punctured (scarified) and discharge their
contents which collect in the handle.
- The liquid is poured off at interval into a large vessel, where it is
allowed to stand until the oil can be decanted and filtered.
c) Machine processes:
- These machine methods have now almost completely replaced the old
hand methods. A centrifuge may be used to separate the emulsion of
oil and water.
III- Extraction method
- This method is used for the preparation of those oils which
decompose by the action of steam or are present in extremely
small quantities in plant organs containing them.
- The minute quantities of oil actually distilling over, are lost
in the large volume of distillation water from which the oil
cannot be recovered.
- This is applied to flowers such as jasmine, gardenia, violet,
and few others.
- The method of extraction is carried out using:
a) Volatile solvents of low boiling point such as hexane.
b) Non-volatile solvents such as fat (lard).
a) Extraction with volatile solvents
- The material containing the volatile oil is extracted
with the volatile solvent with low boiling point by
percolation.
- The volatile oil solution obtained is evaporated
under reduced pressure, where the volatile solvent
will evaporate, leaving the volatile oil behind although
some of the volatile oil will be lost.
Advantage of extraction over distillation:
- Uniform temperatures (usually 50°C) can be maintained during most
of the process.
But the distillation method is a low-cost operation compared to the
extraction process.
a- Extraction with volatile solvents:
Floral concrete:
- In preparing volatile oil with volatile solvents e.g. hexane, pet.ether
the completely concentrated and purified products represent the so called
floral concretes.
- These floral concretes contain the odoriferous principles of the natural
flower perfume plus a considerable amount of plant waxes and color
pigments.
- The concretes are solid and only partly soluble in alcohol 95%.
Absolute:
- By ppt. and eliminating the insoluble waxes from the floral concretes
with strong alcohol and concentrating the filtered alcoholic solutions.
B- Extraction with non-volatile solvents:
This process is used for the preparation of:
* Natural flower oils, where the volatile oil content of the fresh
plant is so small, very expensive, for production of perfumes.
1- Enfleurage method
- A mixture of melted lard is thickly smeared on both surfaces of
each of the glass plates which are enclosed in a wooden frame.
- Each glass plate is sprinkled with flowers to cover its top.
- The plates are left for 24 hours.
- The flowers are then removed and replaced by a fresh supply.
- This is repeated until after some weeks, the fats becomes saturated
with essential oil of the flowers.
- The flowers are then removed and then fat is separated off and is
stirred with absolute alcohol which will take the volatile oil and
leave the fat being insoluble in alcohol.
- The alcoholic extract is carefully cooled and filtered to remove any
traces of fat which might remain in solution.
1- Clove (Caryophylli)
Origin: the dried flower buds of Syzygium
aromatica , Eugenia aromaticum or Eugenia
caryophyllus F. Myrtaceae
Morphology: reddish brown, 16-21 mm
long, the lower stalk like portion
(hypanthium which is an extension of the
receptacle) is about 10-13 mm long,
terminating in 4 triangular sepals and a
dome- shaped head of 4 unexpanded
petals enclosing other parts of the
flower.
Powder: dark brown, with strong
aromatic spicy agreeable odour
and warm spicy agreeable taste
followed by numbness sensation
in the mouth
1. Epidermal cells of sepals, petals
and hypanthium showing
anomocytic stomata.
2.
Oil glands.
Parenchyma with cluster crystals
of calcium oxalate.
4. Xylem vessels and fibres.
3.
5. Fibrous layer of anther and
elongated cells of the filament.
6. Pollen grains: triangular with
truncate apices.
Active constituents:
1. Volatile oil (15 -20%) contains eugenol (85%).
2. Pyrogallol tannin.
Uses:
1. Local anesthetic for toothache.
2. Antispasmodic and carminative.
3. Spice.
4. In manufacture of vanillin.
Chemical test: 1- Test for oil using Sudan III → red
colour.
2- FeCl3 → blue colour.
3- KOH: needle crystals of K eugenate.
Adulteration of clove:
1. Expanded flower
2. Mother clove (fruit): characterized by the presence of
starch.
3. Exhausted clove: lighter than water.
4. Clove stalk: presence of prisms of calcium oxalate and
pseudo crystal sheath.
2- German chamomile
Origin: the dried expanded flower
heads of Matricaria chamomilla F.
Compositae (Asteraceae).
Morphology: flower head
(capitulum) is hemispherical with
hollow receptacle carrying two
types of small sessile flowers called
florets:
Marginal or ray florets (white in
colour)
Central or disc florets (yellow in
colour)
Surrounded by an involucre.
Active constituents: 1- volatile oil contains
matricarin which converted to chamazulene by
heating.
2- flavonoid glycosides.
Uses: 1- carminative, antispasmodic.
2- tranquilizer.
3- local anti-inflammatory for sun burns and diaper
rashes.
Chemical test: sudan III : red colour
3- Anise Fruit
(Fructus Anisi, Aniseed)
Origin: the dried ripe fruits of
Pimpinella Anisum F.
Umbelliferae
Morphology: cremocarp, partly
separated into its mericarps,
often entire attached to a
slender pedicel, 2-12 mm long,
ovoid, enlarged at the base and
tapering at the apex, grayish or
greenish grey in colour rough to
touch due to the presence of
hairs, each mericarp with 5
raised ridges.
Powder: grey, greenish brown or
yellowish brown, having
strong aromatic agreeable
characteristic taste and sweet
strongly aromatic taste,
showing fragments of:
1. non-glandular, unicellular
warty hairs.
2. Branching vitta usually crossed
by the cells of the endocarp.
3. Aleurone grains.
4. Microrosette crystals of
calcium oxalate.
5. Few fibres and pitted
parenchyma.
Active constituents: 1- volatile oil containing anethol
2- fixed oil and protein.
Uses: stimulant, carminative and flavoring agent.
Chemical test: Sudan III
4- Cinnamon Bark
(Cortex Cinnamomi)
Origin: the dried bark of the
branches of the coppiced trees
of Cinnamomum zylanicum F.
Lauraceae. deprived of most of
its cork and cortex and known
as Ceylon Cinnamon.
Morphology: occurs in long,
slender sticks about 1 meter in
length, compound quills.
Powder: a reddish brown powder with
a characteristic pleasant and
aromatic odour and taste,
showing fragments of:
1.
Sclereids, isodiametric, thick
wall, lignified, the outer wall is
less thickened than the others.
2.
Fibres, thick walled lignified,
narrow lumen, slit-shaped pits
and pointed apices.
3.
Starch granules and needle
crystals of calcium oxalate.
4.
Oil cells.
5.
Cork cells are rare.
Active constituents: 0.5-1% volatile oil contains
cinnamaldehyde and eugenol
Mucilage and tannins.
Uses: 1- carminative and flavoring agents
2- Antiseptic and mild astringent.
3- Emmenagogue.
Chemical test: Sudan III, Rhuthenium red, FeCl3 and
KOH for eugenol.
5- Cassia Bark
(Chinese Cinnamon)
Origin: the dried stem bark of
Cinnamomum cassia F.
Lauraceae
Morphology: channeled or
single quills, up to 40 cm
long, earthy brown colour
with patches of the thin
grayish cork.
Powder: differs than cinnamon
in:
1. Odour is less delicate, taste
as cinnamon but slightly
mucilaginous.
2.
Numerous fragments of
cork cells, polygonal with
slightly thick wall, contains
reddish brown content.
3.
Fibres are shorter and
thicker.
Active constituents: volatile oil contains cinnamaldehyde
and no eugenol.
Uses: substitute for cinnamon.
Chemical test: all as cinnamon but negative test for
eugenol
***6- Cardamom Seed
(Semen Cardamomi)‫ الهيل‬-‫ حب الهال‬-‫حبهان‬
Origin: the dried ripe or nearly ripe seeds
of Elettaria cardamomum F. Zingiberaceae,
recently separated from the fruit.
Morphology: cardamom has a strong
aromatic odour and agreeable aromatic
pungent taste. Fruit is ovoid or oblong
capsule, green to pale buff in colour
contains many seeds. Seed is oblong,
ovoid pale ornge to dark reddish brown
usually enveloped by a thin colourless
membranous arillus.
Active constituents: 1- volatile oil contains terpinyl acetate
and cineole.
2- starch, fixed oil and calcium oxalate
Uses: 1- flavoring agent in pharmaceutical industry.
2- spice
Chemical test: Sudan III
Adulterants:
1. Loose seeds: they yield less volatile oil than those which
stored in the pericarp until required for use.
2. Cardamom husk: characterized by the presence of fibres,
sclereids and large vessels which are absent in the seeds.
7- Mentha Herb (Peppermint)
(Herba Mentha Piperitae)
Origin: the dried leaves and
flowering tops of Mentha
piperita F. Labiatae
Powder: green to light olive green, with an
aromatic characteristic odour and an
aromatic taste followed by a sensation
of cold in the mouth. It is characterized
microscopically by the presence of
fragments of:
1.
Epidermal cells with wavy walls and
diacytic stomata.
2.
Non-glandular hairs.
3.
Glandular labiaceous hair, unicellular
stalk multicellular head consists of 8-16
cells radiating from a common center.
4.
Different types of xylem vessels, fibres
and wood parenchyma.
5.
Smooth spherical pollen grains.
6.
NO CALCIUM OXALATE.
Active constituents: 1- volatile oil contains menthol
2- tannin.
Uses:
1. carminative, flavoring agent and aromatic stimulant.
2. Menthol is used in pharmaceutical preparations as local
antipruritic, counter irritant and antiseptic.
3. Used in tooth paste, mouth wash and similar oral
preparations.
4. Recently the oil is used for treatment of colitis.
Chemical test: Sudan III
8- Ginger, Zingiber, Zanjabeel
(Rhizoma Zingiberis)
Origin: the dried rhizome of Zingiber
officinale F. Zingiberaceae,
deprived of the dark outer tissues
and known as unbleached Jamaica
ginger.
Morphology: ginger occurs in
horizontal laterally flattened
branching pieces, 4-16 cm
long,1.5-6.5 cm wide and up to 2
cm thick, pale buff or light brown,
longitudinally striated. It has an
agreeable aromatic odour and an
agreeable pungent aromatic taste.
Powder: powdered ginger is yellowish white
having an agreeable aromatic odour and
an agreeable aromatic pungent taste.
Microscopically, it is characterized by the
presence of:
1. thin walled parenchyma containing starch
granules.
2.
Starch granules: simple, flat, oval, oblong
with terminal protruberance in which
eccentric hilum is situated with
transverse striations.
3.
Thin walled septate fibres.
4.
Non-lignified xylem vessels.
5.
Yellowish brown oleo-resin masses, free
or in cells.
6.
Absence of scleried cells or calcium
oxalate.
Active constituents:
1. volatile oil contains monoterpenes (phellandrene,
camphene, cineole, citral and borneol) and
sesquiterpenes (zingiberene and bisabolene).
2. Resin, starch and mucilage.
Uses:
1. carminative and stimulant.
2. Antiemetic.
3. Antirheumatic.
4. Condiment.