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An aroma compound, also known as an odorant, aroma, fragrance or
flavor Flavor, or flavour, is the perceptual Perception (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area arou ...

flavor
, is a
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemical bonds. A homonuclear molecule, m ...
that has a smell or
odor An odor () or odour (; ) is caused by one or more volatilized s that are generally found in low concentrations that humans and animals can perceive by their of . An odor is also called a "smell" or a "scent", which can refer to either a plea ...
. For an individual chemical or class of chemical compounds to impart a smell or fragrance, it must be sufficiently volatile for transmission via the air to the
olfactory system The olfactory system, or sense of smell, is the sensory nervous system, sensory system used for smelling (olfaction). Olfaction is one of the special senses, that have directly associated specific organs. Most mammals and reptiles have a main ol ...

olfactory system
in the upper part of the nose. As examples, various fragrant fruits have diverse aroma compounds, particularly strawberries which are commercially cultivated to have appealing aromas, and contain several hundred aroma compounds. Generally, molecules meeting this specification have
molecular weight A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion I ...
s of less than 310. Flavors affect both the sense of
taste The gustatory system or sense of taste is the sensory system The sensory nervous system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory neurons (including the sensory re ...

taste
and smell, whereas fragrances affect only smell. Flavors tend to be naturally occurring, and the term ''fragrances'' may also apply to synthetic compounds, such as those used in
cosmetics Cosmetics are constituted mixtures of chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and take ...
. Aroma compounds can be found in various
food Food is any substance consumed to provide Nutrient, nutritional support for an organism. Food is usually of plant, animal or Fungus, fungal origin, and contains essential nutrients, such as carbohydrates, fats, protein (nutrient), proteins, vi ...

food
s, such as fruits and their peels,
wine Wine is an alcoholic drink typically made from Fermentation in winemaking, fermented grapes. Yeast in winemaking, Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different ...

wine
,
spices A spice is a seed A seed is an embryonic ''Embryonic'' is the twelfth studio album by experimental rock band the Flaming Lips released on October 13, 2009, on Warner Bros. Records, Warner Bros. The band's first double album, it was release ...

spices
,
floral scentFloral scent or flower scent is composed of all the Volatile organic compound, volatile organic compounds (VOCs), or aroma compounds, emitted by floral tissue (e.g. flower petals). Floral scent is also referred to as aroma, fragrance, floral odour or ...
,
perfume Perfume (, ; french: parfum) is a mixture of fragrance, fragrant essential oils or aroma compounds (fragrances), Fixative (perfumery), fixatives and solvents, usually in liquid form, used to give the human body, animals, food, objects, and livin ...

perfume
s,
fragrance oil Fragrance oils, also known as aroma oils, aromatic oils, and flavor oils, are blended syntheticA synthetic is an artificial material produced by organic chemistry, organic chemical synthesis. Synthetic may also refer to: In the sense of both " ...
s, and
essential oil An essential oil is a concentrated hydrophobic In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matte ...
s. For example, many form
biochemical Biochemistry or biological chemistry, is the study of chemical process In a scientific Science (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. L ...
ly during the
ripening Ripening is a process in fruit In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. T ...
of
fruit In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the ...

fruit
s and other crops. Wines have more than 100 aromas that form as byproducts of
fermentation Fermentation is a metabolism, metabolic process that produces chemical changes in organic Substrate (chemistry), substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in ...
. Also, many of the aroma compounds play a significant role in the production of compounds used in the food service industry to flavor, improve, and generally increase the appeal of their products. An
odorizer An odorizer is a device that adds an odorant to a gas. The most common type is one that adds a mercaptan liquid into natural gas distribution systems so that leaks can be readily detected. Other types have been used for carbon dioxide fire ex ...
may add a detectable odor to a dangerous odorless substance, like
propane Propane () is a three-carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's ...

propane
,
natural gas Natural gas (also called fossil gas; sometimes just gas) is a naturally occurring hydrocarbon gas mixture consisting of methane and commonly including varying amounts of other higher alkanes, and sometimes a small percentage of carbon dioxid ...

natural gas
, or
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...
, as a safety measure.


Aroma compounds classified by structure


Esters


Linear terpenes


Cyclic terpenes

Note: Carvone, depending on its chirality, offers two different smells.


Aromatic


Amines


Other aroma compounds


Alcohols

* (
strawberry The garden strawberry (or simply strawberry; ''Fragaria × ananassa'') is a widely grown hybrid species Hybrid speciation is a form of speciation Speciation is the evolution Evolution is change in the Heredity, heritable Phenotypi ...

strawberry
) * 1-Hexanol (
herbaceous Herbaceous plants are vascular plants that have no persistent wood, woody stems above ground, including many perennial plant, perennials, and nearly all Annual plant, annuals and Biennial plant, biennials. Definitions of "herb" and "herbaceous" ...
, woody) * ''cis''-3-Hexen-1-ol (fresh cut
grass Poaceae () or Gramineae () is a large and nearly ubiquitous family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain ...

grass
) *
Menthol Menthol is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, and s ...

Menthol
(
peppermint Peppermint (''Mentha'' × ''piperita'', also known as ''Mentha balsamea'' Wild) is a hybrid mint, a cross between watermint and spearmint. Indigenous to Europe and the Middle East, the plant is now widely spread and cultivated in many regions ...
)


Aldehydes

High concentrations of aldehydes tend to be very pungent and overwhelming, but low concentrations can evoke a wide range of aromas. *
Acetaldehyde Ethanal (common name acetaldehyde) is an organic chemical compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds ...
(ethereal) * (green, grassy) * ''cis''-3-Hexenal (green
tomato The tomato is the edible berry A berry is a small, pulpy, and often edible fruit In botany, a fruit is the seed-bearing structure in flowering plants (also known as angiosperms) formed from the ovary after flowering. Fruits are ...

tomato
es) *
Furfural Furfural is an organic compound with the formula C4H3OCHO. It is a colorless liquid, although commercial samples are often brown. It has an aldehyde group attached to the 2-position of furan. It is a product of the dehydration reaction, dehydrat ...

Furfural
(burnt
oat The oat (''Avena sativa''), sometimes called the common oat, is a of grown for its seed, which is known by the same name (usually in the plural, unlike other cereals and ). While oats are suitable for human consumption as and , one of the m ...
s) * *
Isovaleraldehyde Isovaleraldehyde organic compound, also known as 3-methylbutanal, with the formula (CH3)2CHCH2CHO. It is an aldehyde, a colorless liquid at Standard temperature and pressure, STP,Lewis, R.J. Sr.; Hawley's Condensed Chemical Dictionary 15th Edition. ...
– nutty, fruity, cocoa-like * Anisic aldehyde – floral, sweet, hawthorn. It is a crucial component of chocolate, vanilla, strawberry, raspberry, apricot, and others. * (4-propan-2-ylbenzaldehyde) – Spicy, cumin-like, green


Esters

* Fructone (fruity, apple-like) * Ethyl methylphenylglycidate (
Strawberry The garden strawberry (or simply strawberry; ''Fragaria × ananassa'') is a widely grown hybrid species Hybrid speciation is a form of speciation Speciation is the evolution Evolution is change in the Heredity, heritable Phenotypi ...

Strawberry
) * alpha-Methylbenzyl acetate (
Gardenia ''Gardenia'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. ...

Gardenia
)


Ketones

* Cyclopentadecanone (musk-ketone) * (fruity woody floral) * (blood, metallic, mushroom-like) * (fresh bread, jasmine rice) * (fresh bread, tortillas, popcorn)


Lactones

* intense peach flavor * gamma-Nonalactone coconut odor, popular in suntan lotions * delta-Octalactone creamy note * powerful fatty-fruity peach and apricot * Massoia lactone powerful creamy coconut * sweet coconut odor * (
maple syrup Maple syrup is a syrup usually made from the xylem sap of sugar maple, red maple, or black maple trees, although it can also be made from other maple species. In cold climates, these trees store starch in their trunks and roots before winter; t ...

maple syrup
,
curry Curry is a variety of dishes originating in the Indian subcontinent. It uses a combination of spices or herbs, usually including ground turmeric Turmeric (pronounced , also or ) is a flowering plant The flowering plants, also known a ...

curry
,
fenugreek Fenugreek (; ''Trigonella foenum-graecum'') is an annual plant in the family Fabaceae The Fabaceae or Leguminosae,
)


Thiols

*
(2-propanethione) A lightly studied organosulfur. Its smell is so potent it can be detected several hundred meters downwind mere seconds after a container is opened. *
Allyl thiol Allyl mercaptan (AM) is a small molecule allyl derivative and an organosulfur compound derived from garlic and a few other genus ''Allium'' plants. Its formula is C3H6S. It has been shown to be the most effective HDAC inhibitor of known garlic-d ...
(2-propenethiol; allyl mercaptan; CH2=CHCH2SH) (
garlic Garlic (''Allium sativum'') is a species of bulbous flowering plant in the genus ''Allium''. Its close relatives include the onion, shallot, leek, chive, Allium fistulosum, Welsh onion and Allium chinense, Chinese onion. It is native to Central ...

garlic
volatiles and
garlic breath Garlic breath is halitosis Bad breath, also known as halitosis, is a medical symptom, symptom in which a noticeably unpleasant breath odour is present. It can result in anxiety among those affected. It is also associated with Mood disorder, depr ...
) * (Methylthio)methanethiol (CH3SCH2SH), the "mouse thiol", found in mouse urine and functions as a
semiochemical A semiochemical, from the Greek wiktionary:σημεῖον, σημεῖον (''semeion''), meaning "signal", is a chemical substance or mixture released by an organism that affects the behaviors of other individuals. Semiochemical communication c ...
for female mice *
Ethanethiol Ethanethiol, commonly known as ethyl mercaptan and stench, is a clear liquid with a distinct odor. It is an organosulfur compound Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but man ...

Ethanethiol
, commonly called ethyl mercaptan (added to
propane Propane () is a three-carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's ...

propane
or other liquefied-petroleum gases used as fuel gases) * , commonly called ''tert''-butyl mercaptan, is added as a blend of other components to natural gas used as fuel gas. * , commonly called butyl mercaptan, is a chemical intermediate. * Grapefruit mercaptan (grapefruit) *
Methanethiol Methanethiol (also known as methyl mercaptan A thiol () or thiol derivative is any organosulfur compound Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compoun ...

Methanethiol
, commonly called methyl mercaptan (after eating
Asparagus Asparagus, or garden asparagus, folk name sparrow grass, scientific name ''Asparagus officinalis'', is a perennial A perennial plant or simply perennial is a plant Plants are predominantly photosynthetic eukaryotes of the Kingdom ...

Asparagus
) * , also called furfuryl mercaptan (roasted
coffee Coffee is a drink prepared from roasted s, the seeds of from certain s in the ' genus. From the coffee fruit, the seeds are separated to produce a stable, raw product: unroasted ''green coffee''. The seeds are then , a process which transfo ...

coffee
) *
Benzyl mercaptan Benzyl mercaptan is an organosulfur compound with the formula C6H5CH2SH. It is a common laboratory thiol, alkylthiol that occurs in trace amounts naturally. It is a colorless, malodorous liquid. Preparation and occurrence Benzyl mercaptan can be pr ...
(leek or garlic-like)


Miscellaneous compounds

* Methylphosphine and dimethylphosphine (garlic-metallic, two of the most potent odorants known) *
Phosphine Phosphine (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering OrganizationsNational Adhering Organizations in chemistry are the organizations that work as the authoritat ...

Phosphine
(
zinc phosphide Zinc phosphide ( Zn3 P2) is an inorganic In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, prope ...
poisoned bait) *
Diacetyl Diacetyl (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science Cou ...
(
butter Butter is a dairy product Dairy products or milk products are a type of food Food is any substance consumed to provide Nutrient, nutritional support for an organism. Food is usually of plant, animal or Fungus, fungal origin, and contai ...

butter
flavor) *
Acetoin Acetoin, also known as 3-hydroxybutanone or acetyl methyl carbinol, is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical ...

Acetoin
(butter flavor) * Nerolin ( orange flowers) *
Tetrahydrothiophene Tetrahydrothiophene is an organosulfur compound with the formula (CH2)4S. It contains a five-membered ring consisting of four carbon atoms and a sulfur atom. It is the Saturated and unsaturated compounds, saturated structural analog, analog of thi ...

Tetrahydrothiophene
(added to
natural gas Natural gas (also called fossil gas; sometimes just gas) is a naturally occurring hydrocarbon gas mixture consisting of methane and commonly including varying amounts of other higher alkanes, and sometimes a small percentage of carbon dioxid ...

natural gas
) * (
cork taint Cork taint is a broad term referring to a wine fault characterized by a set of undesirable smells or tastes found in a bottle of wine, especially spoilage that can only be detected after bottling, aging and opening. Though modern studies have sh ...
) * Substituted
pyrazine Pyrazine is a heterocyclic aromatic organic compound with the chemical formula C4H4N2. It is a symmetrical molecule with point group D2h. Pyrazine is less basic than pyridine, pyridazine and pyrimidine. It is a ''"deliquescent crystals or wax-lik ...
s


Aroma-compound receptors

Animals that are capable of smell detect aroma compounds with their
olfactory receptor Olfactory receptors (ORs), also known as odorant receptors, are chemoreceptor A chemoreceptor, also known as chemosensor, is a specialized sensory receptor Sensory neurons, also known as afferent neurons, are neuron A neuron or nerve cell is ...
s. Olfactory receptors are cell-membrane
receptors Receptor may refer to: *Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ne ...
on the surface of
sensory neurons Sensory neurons, also known as afferent neurons, are neuron A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapse In the nervous system In biology ...
in the
olfactory system The olfactory system, or sense of smell, is the sensory nervous system, sensory system used for smelling (olfaction). Olfaction is one of the special senses, that have directly associated specific organs. Most mammals and reptiles have a main ol ...

olfactory system
that detect airborne aroma compounds. Aroma compounds can then be identified by
gas chromatography Gas chromatography (GC) is a common type of chromatography In chemical analysis, chromatography is a laboratory technique for the Separation process, separation of a mixture into its components. The mixture is dissolved in a fluid solvent (g ...
-olfactometry, which involves a human operator sniffing the GC effluent. In
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s, olfactory receptors are on the surface of the olfactory epithelium in the
nasal cavity The nasal cavity is a large, air-filled space above and behind the nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for Respiration (physiology), respiration alongside the mouth. Beh ...

nasal cavity
.


Safety and regulation

In 2005–06, fragrance mix was the third-most-prevalent
allergen An allergen is a type of antigen In immunology Immunology is a branch of biology that covers the study of immune systems in all organisms. Immunology charts, measures, and contextualizes the Physiology, physiological functioning of the im ...
in
patch test A patch test is a Medical diagnosis, diagnostic method used to determine which specific substances cause Allergy, allergic inflammation of a patient's skin. Patch testing helps identify which substances may be causing a delayed-type allergic rea ...
s (11.5%). 'Fragrance' was voted
Allergen of the YearAllergen of the Year is an annual "award" of dubious distinction voted upon by the American Contact Dermatitis Society. This is "designed to draw attention to allergens that are very common, under-recognized, merit more attention because they are cau ...
in 2007 by the American Contact Dermatitis Society. A recent academic study in the United States has shown that "34.7 % of the population reported health problems, such as migraine headaches and respiratory difficulties, when exposed to fragranced products". The composition of fragrances is usually not disclosed in the label of the products, hiding the actual chemicals of the formula, which raises concerns among some consumers. In the United States, this is because the law regulating cosmetics protects
trade secret Trade secrets are a type of intellectual property that comprise formulas, best practice, practices, business process, processes, designs, legal instrument, instruments, patterns, or compilations of information that have inherent economic value be ...
s.Fragrances in Cosmetics
/ref> In the United States, fragrances are regulated by the
Food and Drug Administration The United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, st ...
if present in cosmetics or drugs, by the
Consumer Products Safety Commission The United States Consumer Product Safety Commission (USCPSC, CPSC, or commission) is an independent agency of the United States government. The CPSC seeks to promote the safety of consumer products by addressing “unreasonable risks” of inj ...
if present in consumer products. No pre-market approval is required, except for drugs. Fragrances are also generally regulated by the
Toxic Substances Control Act of 1976 The Toxic Substances Control Act (TSCA or TOSCA) is a United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in N ...
that "grandfathered" existing chemicals without further review or testing and put the burden of proof that a new substance is not safe on the
EPA The Environmental Protection Agency (EPA) is an Independent agencies of the United States government, independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon pro ...
. The EPA, however, does not conduct independent safety testing but relies on data provided by the manufacturer. A 2019 study of the top-selling
skin moisturizer White petrolatum Moisturizer or emollient is a cosmetic preparation used for protecting, moisturizing, and lubricating the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main fu ...
s found 45% of those marketed as "fragrance-free" contained fragrance.


List of chemicals used as fragrances

In 2010, the
International Fragrance AssociationThe International Fragrance Association (IFRA) is the global representative body of the fragrance industry. It seeks to represent the collective interests of the industry and promote the safe use of fragrances. The Association was founded in 1973 a ...
published a list of 3,059 chemicals used in 2011 based on a voluntary survey of its members, identifying about 90% of the world's production volume of fragrances.


See also

* ''
Flavour and Fragrance Journal The ''Flavour and Fragrance Journal'' is a bimonthly peer-reviewed Peer review is the evaluation of work by one or more people with similar competencies as the producers of the work ( peers). It functions as a form of self-regulation by qualif ...
'' * '' Fragrances of the World'' * Foodpairing * Odor * Odor detection threshold * Olfaction * Olfactory system * Olfactory receptor * Odorizer, a device for adding an odorant to gas flowing through a pipe * Pheromone * Aroma of wine * Eau de toilette


References

{{DEFAULTSORT:Aroma Compound Organic chemistry Olfaction Flavors, Aroma compound Perfume ingredients