Aroma compound

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Fragrance bottles

An aroma compound, also known as an odorant, aroma, fragrance, flavoring or flavor, 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,<ref name="elhadi">Template:Cite journal</ref> particularly strawberries which are commercially cultivated to have appealing aromas, and contain several hundred aroma compounds.<ref name=elhadi/><ref name="ulrich">Template:Cite journal</ref>

Generally, molecules meeting this specification have molecular weights of less than 310.<ref>Template:Cite journal</ref> 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.<ref name=Ullmann>Template:Ullmann</ref>

Aroma compounds can naturally be found in various foods, such as fruits and their peels, wine, spices, floral scent, perfumes, fragrance oils, and essential oils. For example, many form biochemically during the ripening of fruits and other crops.<ref name=elhadi/><ref name="haug">Template:Cite journal</ref> Wines have more than 100 aromas that form as byproducts of fermentation.<ref name="ilc">Template:Cite journal</ref> 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.<ref name=elhadi/>

An odorizer may add a detectable odor to a dangerous odorless substance, like propane, natural gas, or hydrogen, as a safety measure.

Aroma compounds classified by structure

Esters

Compound name	Fragrance	Natural occurrence	Chemical structure
Geranyl acetate	Fruity, Floral	Rose	File:Geranyl acetate skeletal.svg
Methyl formate	Ethereal		File:Structural formula of methyl formate.svg
Methyl acetate	Sweet, nail polish Solvent		File:Methyl-acetate-2D-skeletal.svg
Methyl propionate Methyl propanoate	Sweet, fruity, rum-like		File:Methyl propionate.svg
Methyl butyrate Methyl butanoate	Fruity	Apple Pineapple	File:Buttersauremethylester.svg
Ethyl acetate	Sweet, solvent	Wine	File:Ethyl-acetate-2D-skeletal.svg
Ethyl butyrate Ethyl butanoate	Fruity	Orange, Pineapple	File:Ethyl butyrate2.svg
Isoamyl acetate	Fruity, Banana, Pear	Banana plant	File:Isoamyl acetate.svg
Pentyl butyrate Pentyl butanoate	Fruity	Pear Apricot	File:Pentyl butyrate.svg
Pentyl pentanoate	Fruity	Apple	File:Pentyl pentanoate.svg
Octyl acetate	Fruity	Orange	File:Octyl acetate.svg
Benzyl acetate	Fruity, Strawberry	Strawberries	File:Benzyl acetate-structure.svg
Methyl anthranilate	Fruity	Grape	File:Methyl anthranilate.svg
Methyl salicylate	Minty, root beer	Wintergreen	File:Methyl salicylate.svg
Hexyl acetate	Floral, Fruity	Apple, Plum	File:Hexyl acetate.png

Linear terpenes

Compound name	Fragrance	Natural occurrence	Chemical structure
Myrcene	Woody, complex	Verbena, Bay leaf	File:Myrcene beta straight acsv.svg
Geraniol	Rose, flowery	Geranium, Lemon	File:Geraniol structure.png
Nerol	Sweet rose, flowery	Neroli, Lemongrass	File:Nerol structure.svg
Citral, lemonal Geranial, neral	Lemon	Lemon myrtle, Lemongrass	File:Geranial structure.png
Citronellal	Lemon	Lemongrass	File:Citronellal-2D-skeletal.png
Citronellol	Lemon	Lemongrass, rose Pelargonium	File:Citronellol-2D-skeletal.png
Linalool	Floral, sweet Woody	Coriander, Sweet basil, Lavender, Honeysuckle	File:Linalool skeletal.svg
Nerolidol	Woody, fresh bark	Neroli, ginger Jasmine	File:Nerolidol.png
Ocimene	Fruity, Floral	Mango, Curcuma amada	File:Alpha-ocimene.svg

Cyclic terpenes

Compound name	Fragrance	Natural occurrence	Chemical structure
Limonene	Orange	Orange, lemon	File:Limonene-2D-skeletal.svg
Camphor	Camphor	Camphor laurel	File:Camphor structure.png
Menthol	Menthol	Mentha	File:Menthol skeletal.svg
Carvone1	Caraway or Spearmint	Caraway, dill, spearmint	File:Carvone.svg
Terpineol	Lilac	Lilac, cajuput	File:Terpineol alpha.svg
alpha-Ionone	Violet, woody	Violet	File:Alpha-ionone-label.png
Thujone	Minty	Wormwood, lilac, juniper	File:Beta-Thujone.svg
Eucalyptol	Eucalyptus	Eucalyptus	File:Eucalyptol.png
Jasmone	spicy, fruity, floral in dilution	Jasmine, Honeysuckle	File:Jasmon structural formation V1.svg

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

Aromatic

Compound name	Fragrance	Natural occurrence	Chemical structure
Benzaldehyde	Almond	Bitter almond	File:Benzaldehyde.png
Eugenol	Clove	Clove	File:Eugenol acsv.svg
Cinnamaldehyde	Cinnamon	Cassia Cinnamon	File:Zimtaldehyd - cinnamaldehyde.svg
Ethyl maltol	Cooked fruit Caramelized sugar		File:Ethyl maltol.png
Vanillin	Vanilla	Vanilla	File:Vanillin.svg
Anisole	Anise	Anise	File:Anisol.svg
Anethole	Anise	Anise Sweet basil	File:Anethole-structure-skeletal.svg
Estragole	Tarragon	Tarragon	File:Estragole acsv.svg
Thymol	Thyme	Thyme	File:Thymol2.svg

Amines

Compound name	Fragrance	Natural occurrence	Chemical structure
Trimethylamine	Fishy Ammonia		File:Trimethylamine chemical structure.png
Putrescine Diaminobutane	Rotting flesh	Rotting flesh	File:Diaminobutane.svg
Cadaverine	Rotting flesh	Rotting flesh	File:Pentane-1,5-diamine 200.svg
Pyridine	Fishy	Belladonna	File:Pyridin.svg
Indole	Fecal Flowery	Feces Jasmine	File:Indol2.svg
Skatole	Fecal Flowery	Feces (diluted) Orange Blossoms	File:Skatole structure.svg

Other aroma compounds

Alcohols

• Furaneol (strawberry)
• 1-Hexanol (herbaceous, woody)
• cis-3-Hexen-1-ol (fresh cut grass)
• Menthol (peppermint)

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 (green, grassy)
• cis-3-Hexenal (green tomatoes)
• Furfural (burnt oats)
• Hexyl cinnamaldehyde
• Isovaleraldehyde – nutty, fruity, cocoa-like
• Anisic aldehyde – 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 (fruity, apple-like)
• Ethyl methylphenylglycidate (Strawberry)
• alpha-Methylbenzyl acetate (Gardenia)

Ketones

• Cyclopentadecanone (musk-ketone)<ref>Template:Cite journal</ref>
• Dihydrojasmone (fruity woody floral)
• Oct-1-en-3-one (blood, metallic, mushroom-like)<ref name="metallic" />
• 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, curry, fenugreek)

Thiols

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• 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)<ref>Template:Cite book</ref>
• (Methylthio)methanethiol (CH₃SCH₂SH), the "mouse thiol", found in mouse urine and functions as a semiochemical for female mice<ref>Template:Cite journal</ref>
• 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, also called furfuryl mercaptan (roasted coffee)
• Benzyl mercaptan (leek or garlic-like)

Miscellaneous compounds

• Methylphosphine and dimethylphosphine (garlic-metallic, two of the most potent odorants known)<ref name="metallic">Template:Cite journal

</ref>

• Phosphine (zinc phosphide poisoned bait)
• Diacetyl (butter flavor)
• Acetoin (butter flavor)
• Nerolin (orange flowers)
• Tetrahydrothiophene (added to natural gas)
• 2,4,6-Trichloroanisole (cork taint)
• Substituted 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.<ref>Template:Cite journal</ref>

In mammals, olfactory receptors are expressed on the surface of the olfactory epithelium in the nasal cavity.<ref name=haug/>

Safety and regulation

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Patch test

In 2005–06, fragrance mix was the third-most-prevalent allergen in patch tests (11.5%).<ref name="autogenerated2005">Template:Cite journal</ref> '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".<ref>Anne Steinemann, "Fragranced consumer products: exposures and effects from emissions", Air Quality, Atmosphere & Health, December 2016, Volume 9, Issue 8, pp 861–866.</ref>

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.<ref>Anne C. Steinemann et al., "Fragranced Consumer Products: Chemicals Emitted, Ingredients Unlisted", Environmental Impact Assessment Review, Vol. 31, Issue 3, April 2011, pp. 328-333.</ref> In the United States, this is because the law regulating cosmetics protects trade secrets.<ref name="FDA fragranaces">Fragrances in CosmeticsTemplate:Dead linkTemplate:Cbignore</ref>

In the United States, fragrances are regulated by the Food and Drug Administration if present in cosmetics or drugs, by the Consumer Products Safety Commission if present in consumer products.<ref name="FDA fragranaces" /> 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 EPA, however, does not conduct independent safety testing but relies on data provided by the manufacturer.<ref>Template:Cite book</ref>

A 2019 study of the top-selling skin moisturizers found 45% of those marketed as "fragrance-free" contained fragrance.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

See also

• Aroma of wine
• Eau de toilette
• Flavour and Fragrance Journal
• Fragrances of the World
• Foodpairing
• Odor
• Odor detection threshold
• Odorizer, a device for adding an odorant to gas flowing through a pipe
• Olfaction
• Olfactory receptor
• Olfactory system
• Pheromone
• vabbing

References

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