An aroma compound, also known as an odorant, aroma, fragrance,

flavoring A flavoring (or flavouring), also known as flavor (or flavour) or flavorant, is a food additive that is used to improve the taste or smell of food. It changes the perceptual impression of food as determined primarily by the chemoreceptors of ...

or flavor, is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

that has a smell or

odor An odor (American English) or odour ( Commonwealth English; see spelling differences) is a smell or a scent caused by one or more volatilized chemical compounds generally found in low concentrations that humans and many animals can perceive ...

. 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, is the sensory nervous system, sensory system used for the sense of smell (olfaction). Olfaction is one of the special senses directly associated with specific organs. Most mammals and reptiles have a main 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 molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

s of less than 310. Flavors affect both the sense of

taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste. Taste is the perception stimulated when a substance in the mouth biochemistry, reacts chemically with taste receptor cells l ...

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 substances that are intended for application to the body for cleansing, beautifying, promoting attractiveness, or altering appearance. They are mixtures of chemical compounds derived from either Natural product, natural source ...

. Aroma compounds can naturally be found in various

food Food is any substance consumed by an organism for Nutrient, nutritional support. Food is usually of plant, animal, or Fungus, fungal origin and contains essential nutrients such as carbohydrates, fats, protein (nutrient), proteins, vitamins, ...

s, such as fruits and their peels,

wine Wine is an alcoholic drink made from Fermentation in winemaking, fermented fruit. Yeast in winemaking, Yeast consumes the sugar in the fruit and converts it to ethanol and carbon dioxide, releasing heat in the process. Wine is most often made f ...

spices In the culinary arts, a spice is any seed, fruit, root, Bark (botany), bark, or other plant substance in a form primarily used for flavoring or coloring food. Spices are distinguished from herbs, which are the leaves, flowers, or stems of pl ...

floral scent Floral scent, or flower scent, is composed of all the volatile organic compounds (VOCs), or aroma compounds, emitted by floral tissue (e.g. flower petals). Other names for floral scent include, aroma, fragrance, floral odour or perfume. Flower sce ...

perfume Perfume (, ) 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 living-spaces an agre ...

s, fragrance oils, and

essential oil An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the ...

s. For example, many form

biochemical Biochemistry, or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology, ...

ly during the

ripening Ripening is a process in fruits that causes them to become more palatable. In general, fruit becomes sweeter, less green, and softer as it ripens. Even though the acidity of fruit increases as it ripens, the higher acidity level does not make t ...

fruit In botany, a fruit is the seed-bearing structure in flowering plants (angiosperms) that is formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate their seeds. Edible fruits in particular have long propaga ...

s and other crops. Wines have more than 100 aromas that form as byproducts of

fermentation Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic molecules, such as glucose or other sugars, are catabolized and reduce ...

. 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 chain alkane with the molecular formula . It is a gas at standard temperature and pressure, but becomes liquid when compressed for transportation and storage. A by-product of natural gas processing and petroleum ref ...

natural gas Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...

, or

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

, 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

* Furaneol (

strawberry The garden strawberry (or simply strawberry; ''Fragaria × ananassa'') is a widely grown Hybrid (biology), hybrid plant cultivated worldwide for its fruit. The genus ''Fragaria'', the strawberries, is in the rose family, Rosaceae. The fruit ...

) * 1-Hexanol (

herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition of ...

, woody) * ''cis''-3-Hexen-1-ol ( fresh cut grass) *

Menthol Menthol is an organic compound, specifically a Monoterpene, monoterpenoid, that occurs naturally in the oils of several plants in the Mentha, mint family, such as Mentha arvensis, corn mint and peppermint. It is a white or clear waxy crystallin ...

(

peppermint Peppermint (''Mentha'' × ''piperita'') is a Hybrid (biology), hybrid species of Mentha, mint, a cross between Mentha aquatica, watermint and spearmint. Indigenous to Europe and the Middle East, the plant is now widely spread and cultivated in m ...

)

Aldehydes

High concentrations of aldehydes tend to be very pungent and overwhelming, but low concentrations can evoke a wide range of aromas. *

Acetaldehyde Acetaldehyde (IUPAC systematic name ethanal) is an organic compound, organic chemical compound with the chemical formula, formula , sometimes abbreviated as . It is a colorless liquid or gas, boiling near room temperature. It is one of the most ...

(ethereal) * Hexanal (green, grassy) * ''cis''-3-Hexenal (green

tomato The tomato (, ), ''Solanum lycopersicum'', is a plant whose fruit is an edible Berry (botany), berry that is eaten as a vegetable. The tomato is a member of the nightshade family that includes tobacco, potato, and chili peppers. It originate ...

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 of sugars, as occu ...

(burnt oats) * Hexyl cinnamaldehyde * Isovaleraldehyde – nutty, fruity, cocoa-like * Anisic aldehyde – floral, sweet, hawthorn. It is a crucial component of chocolate, vanilla,

raspberry The raspberry is the edible fruit of several plant species in the genus ''Rubus'' of the Rosaceae, rose family, most of which are in the subgenus ''Rubus#Modern classification, Idaeobatus''. The name also applies to these plants themselves. Ras ...

, apricot, and others. * Cuminaldehyde (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 (biology), hybrid plant cultivated worldwide for its fruit. The genus ''Fragaria'', the strawberries, is in the rose family, Rosaceae. The fruit ...

) * alpha-Methylbenzyl acetate (

Gardenia ''Gardenia'' is a genus of flowering plants in the coffee family, Rubiaceae, native to the tropical and subtropical regions of Africa, Asia, Madagascar, Pacific Islands, and Australia. The genus was named by Carl Linnaeus and John Ellis after ...

)

Ketones

* Cyclopentadecanone (musk-ketone) * Dihydrojasmone (fruity woody floral) *

Oct-1-en-3-one Oct-1-en-3-one (CH2=CHC(=O)(CH2)4CH3), also known as 1-octen-3-one or amyl vinyl ketone, is the odorant that is responsible for the typical "metallic" smell of metals and blood coming into contact with skin. Oct-1-en-3-one has a strong metallic mus ...

(blood, metallic, mushroom-like) * 2-Acetyl-1-pyrroline (fresh bread, jasmine rice) * 6-Acetyl-2,3,4,5-tetrahydropyridine (fresh bread, tortillas, popcorn)

Lactones

* gamma-Decalactone intense peach flavor * gamma-Nonalactone coconut odor, popular in suntan lotions * delta-Octalactone creamy note * Jasmine lactone powerful fatty-fruity peach and apricot * Massoia lactone powerful creamy coconut * Wine lactone sweet coconut odor * Sotolon (

maple syrup Maple syrup is a sweet syrup made from the sap of maple trees. In cold climates, these trees store starch in their trunks and roots before winter; the starch is then converted to sugar that rises in the sap in late winter and early spring. Ma ...

curry Curry is a dish with a sauce or gravy seasoned with spices, mainly derived from the interchange of Indian cuisine with European taste in food, starting with the Portuguese, followed by the Dutch and British, and then thoroughly internatio ...

fenugreek Fenugreek (; ''Trigonella foenum-graecum'') is an annual plant in the family Fabaceae, with leaves consisting of three small Glossary_of_leaf_morphology#Leaf_and_leaflet_shapes, obovate to oblong leaflets. It is cultivated worldwide as a semiar ...

)

Thiols

* Thioacetone (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 (2-propenethiol; allyl mercaptan; CH₂=CHCH₂SH) (

garlic Garlic (''Allium sativum'') is a species of bulbous flowering plants in the genus '' Allium''. Its close relatives include the onion, shallot, leek, chives, Welsh onion, and Chinese onion. Garlic is native to central and south Asia, str ...

volatiles and

garlic breath Garlic breath is halitosis (bad breath) resulting from the consumption of garlic. Causes The major volatile compounds responsible for garlic breath are allyl methyl sulfide, allyl methyl disulfide, allyl mercaptan, diallyl disulfide, dimeth ...

) * (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, is an organosulfur compound with the formula CH3CH2SH. It is a colorless liquid with a distinct odor. Abbreviated EtSH, it consists of an ethyl group (Et), CH3CH2, attached to a thiol group, SH. It ...

, commonly called ethyl mercaptan (added to

or other liquefied-petroleum gases used as fuel gases) * 2-Methyl-2-propanethiol, commonly called ''tert''-butyl mercaptan, is added as a blend of other components to natural gas used as fuel gas. * Butane-1-thiol, commonly called butyl mercaptan, is a chemical intermediate. * Grapefruit mercaptan (grapefruit) *

Methanethiol Methanethiol (also known as methyl mercaptan) is an organosulfur compound with the chemical formula . It is a colorless gas with a distinctive putrid smell. In small amounts, it is pervasive in nature and found in certain foods, such as some n ...

, commonly called methyl mercaptan (after eating

Asparagus Asparagus (''Asparagus officinalis'') is a perennial flowering plant species in the genus ''Asparagus (genus), Asparagus'' native to Eurasia. Widely cultivated as a vegetable crop, its young shoots are used as a spring vegetable. Description ...

) *

Furan-2-ylmethanethiol Furan-2-ylmethanethiol (2-furanmethanethiol) is an organosulfur compound. It is classified as a furan substituted with a methylthiol group. It is a colourless liquid, but impure samples can appear yellow. It possesses a strong odour of roasted c ...

, also called furfuryl mercaptan (roasted

coffee Coffee is a beverage brewed from roasted, ground coffee beans. Darkly colored, bitter, and slightly acidic, coffee has a stimulating effect on humans, primarily due to its caffeine content, but decaffeinated coffee is also commercially a ...

) * Benzyl mercaptan (leek or garlic-like)

Miscellaneous compounds

* Methylphosphine and dimethylphosphine (garlic-metallic, two of the most potent odorants known) *

Phosphine Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...

( zinc phosphide poisoned bait) * Diacetyl (

butter Butter is a dairy product made from the fat and protein components of Churning (butter), churned cream. It is a semi-solid emulsion at room temperature, consisting of approximately 81% butterfat. It is used at room temperature as a spread (food ...

flavor) * Acetoin (butter flavor) * Nerolin ( orange flowers) * Tetrahydrothiophene (added to

) * 2,4,6-Trichloroanisole (

cork taint Cork taint is a broad term referring to an off-odor and off-flavor wine fault arising from the presence of 2,4,6-trichloroanisole (TCA), a chemical compound that represents one of the strongest off-flavors, and one "generated naturally in foods/b ...

) * 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 crystal or wax-lik ...

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 chemoreceptors expressed in the cell membranes of olfactory receptor neurons and are responsible for the detection of odorants (for example, compounds that have an odor) which give ...

s. Olfactory receptors are cell-membrane receptors on the surface of sensory neurons in the

that detect airborne aroma compounds. Aroma compounds can then be identified by

gas chromatography Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for Separation process, separating and analyzing compounds that can be vaporized without Chemical decomposition, decomposition. Typical uses of GC include t ...

-olfactometry, which involves a human operator sniffing the GC effluent. In

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s, olfactory receptors are expressed 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 in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nas ...

Safety and regulation

In 2005–06, fragrance mix was the third-most-prevalent

allergen An allergen is an otherwise harmless substance that triggers an allergic reaction in sensitive individuals by stimulating an immune response. In technical terms, an allergen is an antigen that is capable of stimulating a type-I hypersensitivi ...

patch test A patch test is a diagnostic method used to determine which specific substances cause allergic inflammation of a patient's skin. Patch testing helps identify which substances may be causing a delayed-type allergic reaction in a patient and ...

s (11.5%). 'Fragrance' was voted Allergen of the Year in 2007 by the American Contact Dermatitis Society. An academic study in the United States published in 2016 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 A trade secret is a form of intellectual property (IP) comprising confidential information that is not generally known or readily ascertainable, derives economic value from its secrecy, and is protected by reasonable efforts to maintain its conf ...

s. In the United States, fragrances are regulated by the

Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respo ...

if present in cosmetics or drugs, by the Consumer Products Safety Commission 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) is a United States law, passed by the United States Congress, Congress in 1976 and administered by the United States United States Environmental Protection Agency, Environmental Protection Agency (EPA), t ...

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 EPA, however, does not conduct independent safety testing but relies on data provided by the manufacturer. A 2019 study of the top-selling skin moisturizers found 45% of those marketed as "fragrance-free" contained fragrance.

List of chemicals used as fragrances

In 2010, the International Fragrance Association 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.

References

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

Aroma compounds classified by structure

Esters

Linear terpenes

Cyclic terpenes

Aromatic

Amines

Other aroma compounds

Alcohols

Aldehydes

Esters

Ketones

Lactones

Thiols

Miscellaneous compounds

Aroma-compound receptors

Safety and regulation

List of chemicals used as fragrances

See also

References