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

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

, is a chemical compound that has a smell or odor. 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 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 held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bio ...

s of less than 310. Flavors affect both the sense of 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 compounds derived from either natural sources, or synthetically created ones. Cosmetics have various purposes. Those designed for personal care and skin care can be used to cleanse or protec ...

. Aroma compounds can naturally be found in various foods, such as fruits and their peels, wine, spices, floral scent,

perfume Perfume (, ; french: parfum) is a mixture of fragrant essential oils or aroma compounds (fragrances), fixatives and solvents, usually in liquid form, used to give the human body, animals, food, objects, and living-spaces an agreeable scent ...

fragrance oil Fragrance oils, also known as aroma oils, aromatic oils, and flavor oils, are blended synthetic aroma compounds or natural essential oils that are diluted with a carrier like propylene glycol, vegetable oil, or mineral oil. To allergic or otherw ...

s, and essential oils. For example, many form biochemically during the ripening of

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

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

may add a detectable odor to a dangerous odorless substance, like propane,

natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon d ...

, or

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

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

peppermint Peppermint (''Mentha'' × ''piperita'') is a hybrid species of 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 of the world.Euro+Med Plantb ...

)

Aldehydes

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

Hexanal Hexanal, also called hexanaldehyde or caproaldehyde is an alkyl aldehyde used in the flavor industry to produce fruity flavors. Its scent resembles freshly cut grass, like ''cis''-3-hexenal. It is potentially useful as a natural extract that pre ...

(green, grassy) * ''cis''-3-Hexenal (green tomatoes) * Furfural (burnt oats) * Hexyl cinnamaldehyde * Isovaleraldehyde – nutty, fruity, cocoa-like *

Anisic aldehyde 4-Anisaldehyde, or ''p''-Anisaldehyde, is an organic compound with the formula CH3OC6H4CHO. The molecule consists of a benzene ring with an formyl and a methoxy group. It is a colorless liquid with a strong aroma. It provides sweet, floral and ...

– floral, sweet, hawthorn. It is a crucial component of chocolate, vanilla, strawberry, raspberry, apricot, and others. * Cuminaldehyde (4-propan-2-ylbenzaldehyde) – Spicy, cumin-like, green

Esters

Fructone Fructone, also known as apple ketal and applinal, is a synthetic aroma compound with a fruity, apple-like smell with pineapple, strawberry, and woody aspects reminiscent of pine trees. Chemistry Fructone is usually synthesized from ethyl ace ...

(fruity, apple-like) *

Ethyl methylphenylglycidate Ethyl methylphenylglycidate, commonly known as strawberry aldehyde, is an organic compound used in the flavor industry in artificial fruit flavors, in particular strawberry. Uses Because of its pleasant taste and aroma, ethyl methylphenylglyci ...

( Strawberry) * alpha-Methylbenzyl acetate ( Gardenia)

Ketones

* Cyclopentadecanone (musk-ketone) * Dihydrojasmone (fruity woody floral) * Oct-1-en-3-one (blood, metallic, mushroom-like) *

2-Acetyl-1-pyrroline 2-Acetyl-1-pyrroline (2AP) is an aroma compound and flavor that gives freshly baked bread, jasmine rice and basmati rice, the spice ''pandan'' (''Pandanus amaryllifolius''), and ''bread flowers'' (''Vallaris'' ''glabra'') their customary smell. ...

(fresh bread, jasmine rice) * 6-Acetyl-2,3,4,5-tetrahydropyridine (fresh bread, tortillas, popcorn)

Lactones

gamma-Decalactone ''gamma''-Decalactone is a lactone and aroma compound with the chemical formula C10H18O2. It has an intense-peach flavor. It is present naturally in many fruits and fermented products. It is particularly important in the formulation of peach ...

intense peach flavor *

gamma-Nonalactone ''gamma''-Nonalactone is a chemical compound found in bourbon whiskey. See also * delta-Nonalactone, δ-Nonalactone * Cyclotene References

Gamma-lactones {{organic-compound-stub ...

coconut odor, popular in suntan lotions *

delta-Octalactone ''delta''-Octalactone is a lactone and aroma compound with a creamy cocoa, coconut, and peach The peach (''Prunus persica'') is a deciduous tree first domesticated and cultivated in Zhejiang province of Eastern China. It bears edible juicy ...

creamy note * Jasmine lactone powerful fatty-fruity peach and apricot * Massoia lactone powerful creamy coconut *

Wine lactone Wine lactone is a pleasant smelling compound found naturally in apples, orange juice, grapefruit juice, orange essential oil, clementine peel oil and various grape wine Wine is an alcoholic drink typically made from fermented grapes. Ye ...

sweet coconut odor * Sotolon ( maple syrup, curry, fenugreek)

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 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, dimet ...

) * (Methylthio)methanethiol (CH₃SCH₂SH), the "mouse thiol", found in mouse urine and functions as a semiochemical for female mice * Ethanethiol, commonly called ethyl mercaptan (added to propane 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, commonly called methyl mercaptan (after eating Asparagus) *

Furan-2-ylmethanethiol Furan-2-ylmethanethiol (2-Furanmethanethiol) is an organic compound containing a furan substituted with a sulfanylmethyl group. It is a clear colourless liquid when pure, but it becomes yellow coloured upon prolonged standing. It possesses a stro ...

, also called furfuryl mercaptan (roasted coffee) *

Benzyl mercaptan Benzyl mercaptan is an organosulfur compound with the formula C6H5CH2SH. It is a common laboratory alkylthiol that occurs in trace amounts naturally. It is a colorless, malodorous liquid. Preparation and occurrence Benzyl mercaptan can be prepare ...

(leek or garlic-like)

Miscellaneous compounds

Methylphosphine Methylphosphine is the simplest organophosphorus compound with the formula CH3PH2, often written MePH2. It is a malodorous gas that condenses to a colorless liquid. It can be produced by methylation of phosphide salts:W. L. Jolly “Methylphosphi ...

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 flavor) *

Acetoin Acetoin, also known as 3-hydroxybutanone or acetyl methyl carbinol, is an organic compound with the formula CH3CH(OH)C(O)CH3. It is a colorless liquid with a pleasant, buttery odor. It is chiral. The form produced by bacteria is (''R'')-acetoin. ...

(butter flavor) * Nerolin ( orange flowers) *

Tetrahydrothiophene Tetrahydrothiophene is an organosulfur compound with the formula (CH2)4S. The molecule consists of a five-membered saturated ring with four methylene groups and a sulfur atom. It is the saturated analog of thiophene. It is a volatile, colorle ...

(added to

) * 2,4,6-Trichloroanisole ( cork taint) *

Substituted A substitution reaction (also known as single displacement reaction or single substitution reaction) is a chemical reaction during which one functional group in a chemical compound is replaced by another functional group. Substitution reactions ar ...

pyrazines

Aroma-compound receptors

Animals that are capable of smell detect aroma compounds with their olfactory receptors. Olfactory receptors are cell-membrane receptors on the surface of sensory neurons in the olfactory system that detect airborne aroma compounds. Aroma compounds can then be identified by gas chromatography-olfactometry, which involves a human operator sniffing the GC effluent. In mammals, 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 nasal ...

Safety and regulation

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

allergen An allergen is a type of antigen that produces an abnormally vigorous immune response in which the immune system fights off a perceived threat that would otherwise be harmless to the body. Such reactions are called allergies. In technical t ...

in patch tests (11.5%). 'Fragrance' was voted

Allergen of the Year Allergen of the Year is an annual award 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 causing significant allergi ...

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 secrets.Fragrances in Cosmetics
/ref> 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 federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...

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 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 executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...

. 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