Plants & Human Affairs (BIOL106)  -  Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; ssaupe@csbsju.edu; http://www.employees.csbsju.edu/ssaupe

Stimulating the Senses - Essential Oils

I.  What is an essential oil? 

A.  Definition
     An aromatic liquid (oil).  They usually smell pleasant.  Since these oils have an odor or essence, they are called “essential oils." 

B.  Fixed vs. volatile oil
    Essential oils are volatile, or in other words, they evaporate readily.  In contrast, the fixed oils like corn, safflower and peanut, do not evaporate.   The Grease Spot Test is a test to determine whether an oil is volatile or fixed.  Simply spot a small sample of the oil on a sheet of paper.  If it leaves an oily mark, like after eating some potato chips, the oil is fixed.  If it disappears, it is an essential oil.

C.  Chemistry
    Essential oils are a diverse mixtures of molecules.  The kind and concentration of  molecules in the oil determines its odor.  The molecules typically have 20 carbon atoms or fewer and are hydrocarbons, terpenes, alcohols, phenols, esters, aldehydes and ketones.  Essential oils are soluble in organic solvents (i.e., ether).

D.  Odor Perception
    Why do essential oils have an odor?  The molecules bind to receptors on olfactory neurons that are part of the olfactory bulb in the brain.  The shape of the molecule is important - it determines which neurons are activated and send signal to brain.  The concentration is also important - too much can be repulsive.  Sense of smell adapts rapidly and becomes insensitive..  Sensitivity to odor varies with gender.  For example, females are able to identify more different odors than men and this ability seems to increase during pregnancy (Hypothesis - a way for females to avoid exposing fetus to rotting food, etc.?)

II.  Plants and essential oils

A.  Occurrence
    Essential oils occur in numerous different plants, but especially tropical and subtropical species.  They occur in more than 60 families and are especially common in the Mint, Citrus, Laurel, Myrtle, Geranium and Carrot families. Most of our commercially-important essence producing plants come from Asia, Africa and tropical America. 

B. Botany
    Essential oils are found in all parts of the plant, including flowers, roots and leaves.  Different organs usually yield different oils.  The actual oil that is produced is dependent on plant age, maturity and climate.  The oils are usually produced in glands or hairs or ducts in or on the plant. 

C. Why do plants produce essential oils?
    Among the reasons are:  (1) to attract pollinators; (2) deter herbivores; (3) used to combat other plants (allelopathy); and (4) antimicrobial activity.  There are likely other functions, too.  However, the oils are probably not waste products of normal metabolic activities as once suggested.
 

III. Human Uses of Essential Oils/Oil-Containing Plants

A.  Uses

1. give odor (and flavor) to spices

2. give odor to perfumes, soaps, toiletries, and cosmetics; 

3. act as antiseptics and medicines.  The main premise of aromatherapy is that essential oils can affect our mood, etc.  Although of the claimed benefits seem highly exaggerated (i.e., pseudoscience), there is research that clearly supports a role of essences in treating human disease.  For example, recent research suggests that odor and essences may be an important treatment for seasonal affective disorder (SAD).

4. insecticides; and

5. manufacture of many things including plastics, polish, ink and glue. 

B.  Why do humans put spices in food?

• H1 - "Liven" up foods (=taste better, for pleasure)

• H2 - Help to preserve foods (e.g., due to antimicrobial properties).  High frequency of spice use in tropical areas without refrigeration provides support for this hypothesis.

• H3 - Cover up the taste of food spoilage (disguise unpleasant tastes)

• H4 - Communicate with spiritual world via religious ceremonies (e.g., incense, embalming)

C.  Why do humans wear perfumes?

• H1 - For pleasure (simply to smell good)

• H2 - Medicinal value - reduce skin and other infections, etc. (e.g., aromatherapy; workers in perfume labs in France are said to have fewer lung and bronchial disorders)

• H3 - Cover up body odor (especially important when people were less conscious of hygiene)

• H4 - ability to detect correlated with immune system function.

• H5 - increase perspiration rate and help cool the body; important in the tropics

• H6 - to attract a mate (i.e., pheromones).   Pheromones - volatile hormones that are released by one individual that influences the behaviour of another individual.  Many examples from the animal kingdom: (a) sexual attractants (cockroaches, moths); (b) truffles - release odor that is sex hormone in testes of boar; (c) etc.  Perceived in specialized structures in nasal cavity (vomernasal organs) which are important in reproductive behavior. 

D.  Do humans have pheromones? 
    Humans are diurnal which means that smell has not been as well developed.  However evidence:  (a) we each have a unique odor.  If you wear a shirt, without any deodorant or other identifying scent, most can identify their shirt from those worn by other individuals; (b) female menstrual cycles tend to synchronize when living in close quarters; (c) Columbus reported that natives could identify footprints by smell; (d) male and female volunteers shown pictures of clothed women rated them more attractive when exposed to the sex hormone from the truffle; (e) small pits detected in nasal passage that may serve as VMO; (f) etc.

IV.  Extracting Essences from Plant Material
   The technique must be gentle because the oils are easily changed.  There are three major techniques:

A.  Distillation
   The plant material is placed in water, heated to a boil and the steam carrying the essential oil is condensed and collected in a receiver flask.

B.  Steam Distillation
   This is similar to regular distillation except the plant material is suspended above the water.  The plant material is extracted with steam. 

C.  Effleurages (Cold fat extraction)
   This technique is especially good for delicate and easily changed oils and for those plants (flowers) that continue to produce essential oils after they’ve been harvested.  In this method, lard (tallow) is spread on a glass plant and flower petals are laid on the surface.  When one layer is finished, the process is repeated essentially making a lard/glass plate sandwich.  The odor is absorbed by the lard.  The flowers are removed and then replaced by others until the lard is saturated with essence.  The lard is then extracted with alcohol to remove the essence but not the fat.

D.  Solvent extraction
   The plant material is directly mixed with solvent.  This is a popular method because it is simple and inexpensive.  It is good for plant material that doesn’t continue to produce odors.

E.  Expression
   Mostly used with citrus oils.  The rind is scored and the oil is collected under pressure.


V.  A Survey of Some Essential Oils

A.  Allspice
    Derived from the berry of Pimenta dioica, a tree native to the West Indies.  Much of world crop is grown in Jamaica.    The berry is steam-distilled to yield an oil with a general spice note.

B.  Ambergris - secretion of sperm whales.  
    Since whales eat lots of cuttlefish, which are like squid and have a hard “bone” (used for parakeets), the whales secrete ambergris to protect the lining of the gut.  Ambergris is now obtained synthetically, to protect sperm whales which are endangered. 

C.  Citronella
    Derived from the leaves of the grass, Cymbopogon nardus, which is native to India and Sri Lanka.  Used in soap making, i.e., Ivory Soap,  because of its germicidal action.  Citronella also repels insects.

D.  Cloves
    Derived from the undeveloped flower buds of Syzgium aromaticum,  which is probably native to the Moluccas in Indonesian.  The hand-picked buds are distilled to produce a spicy-sweet odor.  The leaves also produce an oil. One of the main ingredients, eugenol, is used as an anesthetic in dentist offices.

E.  Coriander
    Derived from the seeds of coriander (Coriandrum sativum) which is native to southern Europe and Near East.  Pleasant odor, spicy, sweet and somewhat woody.  Used more for flavor than fragrance.  Russia is the major producer.

F.  Fennel
    Obtained from the seeds of fennel (Foeniculum vulgare), which is a member of the carrot family native to the Mediterranean.

G.  Lavender
    Derived from the flowers of Lavandula angustifolia and relatives (Lavandula hybrida, which is a hybrid).  France is a major producer, but it is also grown in Spain, Italy, s. Russia and Tasmania.  The flowering tops and stalks are steam distilled.  Refreshing floral-herbal odor with balsamic undertones. 

H.  Lemon
    Expressed from the peel of lemon, Citrus limonia, a small tree native to China.   Many areas produce lemon oil including California, Sicily, Brazil and Israel.  Lemon grass oil is derived from Cympopogon citralis. 

I.  Myrrh
    Sweet smelling resin from trees in the genus Commiphora, which are native to Africa and southwest Asia. 

J.  Oil of bay
    Odor is strong and spicy.  The oil is derived from the leaves of Laurus nobilis, the laurel.   The leaves were also used as crown of victors in Rome.  Native of the Mediterranean.

K.  Orange
    The peel of the sweet orange, Citrus sinensis, is expressed from the oil.   Especially produced in Sicily, Israel, Spain Florida, California and Brazil. 

L.   Patchouli
    Derived from the leaves of Pogostemon cablin, a plant in the mint family native to the Philippines.  China, India, Indonesia, and Philippines are major producers.  The leaves and stems are cut and steam distilled.  The resultant oil is allowed to age.   The leaves yield about 3-5% oil by dry weight.  This oil was especially popular during the 1960’s.

M  Sassafras
    Derived from the roots of Sassafras albidum, an understory tree native to the eastern US.  The active ingredient is safrole, which has a root-beer like odor.  Many people make tea from sassafras roots, but safrole is a suspected carcinogen.

N.  Sweet birch
    This oil with a wintergreen-odor is derived from the sap of the sweet birch tree, Betula lenta.  This tree is native to the eastern US. 

O.  Ylang ylang
    Derived from flowers of Cananga odorata, a tree in the Magnolia family that is native to Indonesian and the Philippines.


V.  Perfumes

A.  A brief history of perfumes
   Perfume comes from the Latin words, "per" - meaning through and "fumus" - for air or smoke.  Thus, perfume literally translates into “through the air”, which is how the odors reach our nose.  Perfumes have had a long and influential role in world history since the beginning of recorded history.  They were particularly important in India, China, Babylon, Egypt, Rome and Greece.  This is particularly interesting since they are not necessary (essential) for survival and are mostly products of vanity.  Today perfumes are a multimillion-dollar industry.  Perfumes were first used in religious ceremonies.  They stimulated European exploration and global colonization.  Many were prized as highly as gold. 

B. Perfume Making
    The perfume master works like a composer mixing different fragrances, called notes, to produce a perfume.  The perfumes are classified by the dominant "note" into groups or families.  These are (including an example):  (1) chypre - patchouli; (2) citrus - lemon, orange; (3) floral - lily of the valley, frangipani, Magnolia; (4) Fougere - lavender; (5) green - spearmint, thyme;  (6) Oriental - ylang ylang, clove; (7) Woodsy - cedar, balsam.  The largest amount of money spent on the development of a new perfume is in marketing. 

C.  Ingredients
    Few perfumes are pure essential oils, most are mixtures of:   

1. Odorants - the basic ingredients that give the perfume its odor.  The odorants can be: (a) concretes - immerse the plant in solvent to extract the oil and then evaporate the solvent; or (b) absolutes - extract the concretes with alcohol; or (c) distilled oils; or (d) expressed oils.  Most perfumes are mixtures of absolutes.  Synthetics are rapidly replacing natural plant odorants; 

2. Fixatives - mostly animal products, like musk, civet and ambergris, that serve to retard evaporation of the oil and to equalize the volatility of the ingredients in the essential oils; and

3. Alcohol - the amount varies but is usually in a ratio of 8 parts alcohol to 2 parts essential oil.