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WHAT
MAKES AN ESSENTIAL OIL SMELL THE WAY IT DOES
Citrus oils are obtained from various Citrus
species found within the family of Rutaceae and the subfamily
Aurantioideae. Citrus oils are located as glands within the peel and the
cuticles of the fruits. Some
citrus oils are also found within the leaves (Petitgrain) and flower parts
(Neroli). Peel and cuticle
oils are removed mechanically by cold pressing and since cold pressing
yields a watery emulsion, this emulsion is then subjected to the
centrifuge to separate out the essential oil.
The resultant product will then always have bits of the wax and
other organic matter left in it which is why this essential is subject to
age and when chilled will become murky. Cold-pressing is the favored
method of extraction because steam distillation yields an oil of inferior
quality (with the exception of West Indian Lime peel oil).
Depending on the
variety of the fruit, peel oils yield an essential oil content of
0.5-5.0%.
Main producing areas are the Mediterranean countries of
No single compound is responsible for the characteristic odor of
any citrus oil. Odor is due to
the fact that citrus odor is a complex mixture of related metabolites of
terpenes and secondary metabolites of unsaturated fatty acids.
The individual odors of the different citrus fruits and their
various cultivars are not due to various different chemicals but
rather to the proportions of the various chemical components.
To identify the odor of any one citrus over another, it is as
important to know the odor by your senses (strength, quality and
perception), as it is to have a good chemical analysis.
Two components are necessary for a citrus odor, that is, limonene
and citral. The major
component of most citrus odor is (+)-limonene which can be up to 97% of
the oil. It is responsible for
the base sensory character of the citrus oils.
(-)-limonene is another terpene that possesses a different odor
such as that found in the pines, peppermint and eucalyptus oils.
Fatty aldehydes also contribute to the aroma odor of citrus,
especially octanal and decanal. Citral,
an aldehyde that is also part of the chemistry of citrus oils, always
occurs as a mixture of its stereoisomers geranial
and neral. (A stereo or optical isomer is identical mirror-image forms of
a component, one occurring in d or dextro=right or clockwise form and the
other l or laevo=left in counter-clockwise form. Think of looking at your
hand and then in the mirror.) `
The sesquiterpene ketone (+)-nootkatone possesses a citrus-like
aroma and a bitter taste and occurs in all citrus peel oils.
It contributes a lot to the overall aroma character of any oil in
which it is found. Its other
(-)-nootkatone-ent lacks the citrus aroma.
The stereoisomeric farnesenes occur in all citrus oils.
They are very important for apple flavor.
The
isomeric sinensals are aldehydes of the corresponding farnesenes and are
found in all citrus oils. Even
trace amounts of these aldehyde components have high aroma value because
of their strength of odor.
Cold-pressed oils also contain up to 4% of low volatile
constituents, such as flavonoids or triterpenes that are the bitter
principle. 8.1.1
Orange peel oil
Sweet Orange peel oil [(Citrus
sinensis (L.) Osbeck]. is the most important of the citrus oils.
It yields up to 0.5% by cold-pressing. It is mainly produced in the
south of Italy, Spain, Portugal, Florida and Brazil.
(+)-limonene is the main constituent of this oil.
The aldehyde content of Sweet Orange oil is the measure of the oil.
The preferred Valencia oil possesses up to 3% aldehydes. One of
which is decadienal with an extremely high aroma value.
Other constituents that contribute to the character and quality of
Orange oil are the sinensals. x-sinensal has a high orange aroma scent and low odor threshold
while b-sinensal has a
metallic-fishy note that can be very objectionable.
The difference between Orange and Grapefruit oil can be as simple
as the amount of (+)-valencene. When the amount of a-terpineol
exceeds normal level, off-notes occur.
This terpineol forms during the aging or oxidation of orange juice.
(Some essential oil of Orange is indeed produced from Orange
Juice). The acetates contribute to the floral notes of Orange oil.
The bitter Orange tree (Citrus
aurantium L.) is used to produce the expensive Neroli flower oil while
Petitgrain of Bigarade is produced from the leaves and small branches.
The bitter peel oil differs from Sweet Orange oil less by its
volatile composition then by its bitter taste that is caused by
non-volatile constituents. 8.1.2
Mandarin Oil
Mandarin
(Citrus reticulata Blanco) and the cold-pressed oils of Tangerine and
Clementine contain considerable amounts of methyl N-methyl anthranilate.
According to some, if you mix this component with thymol in correct
proportions you can duplicate a scent that is reminiscent of Mandarin. Add
the terpenes of y-terpinene and --b-pinene
and you can get an even more natural
scent. a-sinensal is
abundant in Mandarin oil up to 0.2%. 8.1.3
Lemon Oil
Lemon oil (Citrus limon (L.) Burm. f.), mostly of Sicilian or South American
origin, is very much used in flavors and fragrances.
It seems to have originated in southeastern China. Others consider
the Lemon to be a native of India. The ancient Roman despite the vast
extent of their empire did not know the Lemon.
Lemon juice oil
contains up to 300 compounds. It is mainly (+)-limonene and also (-)-b-pinene
and with terpinene-4-ol is responsible for the green, peely odor that one
associates with Lemon oil. Other
components are citral that is an aldehyde that is very important as far as
odor and flavor are concerned. The difference between some types of Lemon
oil can be the ratio between citronellal and citral. 8.1.4
Grapefruit Oil
The
peel of (Citrus paradisi
Macfaden) or Grapefruit oil is cold pressed.
The fresh, fruity top-note is due to p-menth-1-en-8-thiol.
This component is present only in very low amounts.
Grapefruit oil is sesquiterpene rich, which is unusual in citrus
oils. Nootkatone is mainly
responsible for the odor of the Grapefruit and contributes to the bitter
flavor of the juice. Linaloöl
oxides, which are found in many essential oils, constitute the second most
important class of compounds. Also
found in the essential oil is epoxycaryophyllene, first found in Verbena
oil, possesses a pleasant woody, balsamic odor. 8.1.5
Bergamot Oil
The unripe peel of (Citrus
bergamia Risso & Poit.) is cold-pressed.
The fruit is bitter and inedible, however, it is available candied
and eaten with bitter Coffee as a sweetmeat in Greece. The fruit yields
about 0.5% essential oil. The
tree is kept at about 15 feet in height and grown in Calabria, an Italian
province. Bergamot oil is the
only Citrus oil in which limonene is not the dominant component.
It is however, rich in linaloöl and linalyl acetate up to 50%.
Oxygenated derivatives of the hydrocarbons of caryophyllene,
germacrene D, farnesene and bisabolene contribute to the typical odor of
Bergamot. The strong woody odor of the aldehyde bergamotenal has been also
known in Costus root oil. 8.1.6
Lime Oil
The
so-called distilled lime is prepared by steam distillation of whole fruits
of (Citrus aurantifolia (Christm.
& Panz.) Swingle). This
steam-distilled oil is more important in the fragrance and perfumery
industry than the cold-pressed oil. The
more expensive cold-pressed oil is more like Lemon oil than what we
associate organoleptically to Lime peel oil. Germacrene B has a
woody-spicy odor that contributes to the fresh odor of Lime Peel oil.
Lime, ummm!
Originally, Petitgrain, which means “small seed” was actually
distilled from the immature and small, round green fruits of the Citrus
trees. Of course, if you
distill the fruits then there will be no mature fruit to eat or preserve.
So eventually, the distillation was limited to the leaves and small
branchlets but the oil is still called Petitgrain.
Petitgrain
is produced by steam distilling the leaves and small branches of certain
citrus trees. The yields is
0.25-0.5%. The most important
of the Petitgrain oils comes from the Bitter Orange tree. Paraguay is a
big producer of low end Petitgrain. Higher
quality Petitgrain comes from France and Italy.
Petitgrain has a strong, bittersweet, floral and somewhat woody
odor, sometimes vegetative (bad), dry and a bit leathery. 80% of the yield
is made up of linalyl acetate and linaloöl in a proportion of 2:1.
The woody smell is from the sesquiterpene alcohol, spathulenol.
Aldehydes contribute to the odorous principle, even though they are
in small amounts. Another
important constituent is the pyrazines with their Galbanum-like green
notes.
It is important to mention that the trace components in Petitgrain
leads to a good scent and especially in perfumery where they are important
when the scent needs to be reconstituted.
Blossoms of the true
bitter (sour) orange tree, Citrus aurantium Linnaeus, subsp. amara L., on being distilled yield
Neroli bigarade oil. If, on the other hand, the leaves and petioles (leaf
stalk) are distilled, oil and hydrosol of Petitgrain Bigarade is obtained.
The word Petitgrain comes
from a French word, meaning the 'little' and 'seed, fruit or berry'. Oil
of Petitgrain is also distilled in Paraguay.
However, in Paraguay, the plant that is distilled is a hybrid of
the sweet and the bitter Orange that has gone wild and thus the oil and
hydrosol is of lower quality.
True Petitgrain oil and hydrosol should originate exclusively from
the true bitter Orange tree. These distillations show that the oil will
have a relatively high laevorotation and the presence of leaves from sweet
Orange trees will result in oils of lower laevorotation, or even
dextrorotation.
The quality of Petitgrain depends on various factors: 1.
The leaf material should originate exclusively from the bitter or sour
Orange tree. 2.
The leaf material should not contain any wooden branches, nor any small
unripe fruit (in spite of the name). 3.
The leaf material should be distilled rapidly and with direct steam that
is generated in a separate boiler. The leaves must not be immersed in
water, as this will cause hydrolysis of the linalyl acetate, which is the
most important constituent. Properly distilled the oil and hydrosol will
have high ester content. 4. The plants of Southern France bloom in May and June and this cutting is used for Neroli production. The leaves and petioles are harvested from the pruning after the Neroli harvest, which is from late June to October.
Petitgrain oil and hydrosol is thus produced from the Bitter Orange
tree after the harvest of the flowers (for Neroli); leaves and stalks are
freshly picked in July-October and freshly and immediately distilled for
the best product.
The quality if Petitgrain oil can be evaluated by its
physicochemical properties. Here are the properties of genuine Petitgrain
distilled in Southern France as outlined in Guenther's work.
It
should be emphasized that American producers wishing to produce Petitgrain
oil and hydrosol be very careful as to the citrus variety they use, time
of harvesting and the type of distillation. 8.3
Neroli Oil
850
kg of carefully picked Orange flowers yields 1 kg of Neroli oil after
steam distillation. Annually
2-3 tons is produced, mainly in North Africa.
The oil possesses a strong. Floral, powdery aldehydic odor, very
fresh with a warm base note that resembles freshly dried hay.
It does resemble Petitgrain in its odor and often Petitgrain is
used to adulterate Neroli oil. Ocimenes
are higher in Neroli than Petitgrain. Also limonene, linaloöl and linalyl
acetate occur in larger amounts than Petitgrain.
Indole which possesses a powerful exotic floral note at high
dilution and a somewhat fresh breast-fed baby shit odor when not diluted
separates and differentiates Neroli from Petitgrain.
This indole odor is sometimes very prevalent in the Neroli
hydrosol. Methoxypyrazine contributes to a green character, which also is
the interesting green note in Galbanum and Green Peppers.
Nootkatone is not present in either Petitgrain or in Neroli. OTHER
INTERESTING CITRUS:
Yuzu, a Grapefruit type; Blood Orange with blackish flesh, dark
essential oil and raspberry flavored juice; Fingered Citron whose rind is
candied and eaten, essential oil is not known; Brain fruit whose leaves
are called Keffir Lime leaves, not known what juice, if any, is used for,
essential oil; and Limequats ?
-The
end- Bibliography: Citrus Notes: Citrus oils are used in the perfumery business to impart a fresh, sparkling note to any blend. They are usually not overpowering. They can be used in up to 25% as the base for classic type of eau de cologne. Citrus oils harmonize with a large number of other essential oils and they are used in different concentrations in almost all scent blends and modern perfumes. In combination with Lavender oil, citrus oils are the basis for English Lavender, which is an 1826 creation. High concentrations of citrus oils are in Chanel No. 5(1921). Also of importance are the citrus oils in pop drinks like Coca-Cola and others. ©All
Rights Reserved 2003, 2004. No part of this article may be used |
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Plant Project · 219 Carl Street · San Francisco, CA 94117
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