Chemistry:Aroma compound

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Short description: Chemical compound that has a smell or odor
Fragrance bottles

An aroma compound, also known as an odorant, aroma, fragrance or flavoring, 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,[1] particularly strawberries which are commercially cultivated to have appealing aromas, and contain several hundred aroma compounds.[1][2]

Generally, molecules meeting this specification have molecular weights of less than 310.[3] 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.[4]

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.[1][5] Wines have more than 100 aromas that form as byproducts of fermentation.[6] 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.[1]

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
Geranyl acetate skeletal.svg
Methyl formate Ethereal
Structural formula of methyl formate.svg
Methyl acetate Sweet, nail polish
Solvent
Methyl-acetate-2D-skeletal.svg
Methyl propionate
Methyl propanoate 		Sweet, fruity, rum-like
Methyl propionate.svg
Methyl butyrate
Methyl butanoate 		Fruity Apple
Pineapple
Buttersauremethylester.svg
Ethyl acetate Sweet, solvent Wine
Ethyl acetate2.svg
Ethyl butyrate
Ethyl butanoate 		Fruity Orange, Pineapple
Ethyl butyrate2.svg
Isoamyl acetate Fruity, Banana,
Pear 		Banana plant
Isoamyl acetate.svg
Pentyl butyrate
Pentyl butanoate 		Fruity Pear
Apricot
Pentyl butyrate.svg
Pentyl pentanoate Fruity Apple
Pentyl pentanoate.svg
Octyl acetate Fruity Orange
Octyl acetate.svg
Benzyl acetate Fruity, Strawberry Strawberries
Benzyl acetate-structure.svg
Methyl anthranilate Fruity Grape
Methyl anthranilate.svg
Methyl salicylate Minty, root beer Wintergreen
Methyl salicylate.svg
Hexyl acetate Floral, Fruity Apple, Plum
Hexyl acetate.png

Linear terpenes

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

Cyclic terpenes

Compound name Fragrance Natural occurrence Chemical structure
Limonene Orange Orange, lemon
Limonene-2D-skeletal.svg
Camphor Camphor Camphor laurel
Camphor structure.png
Menthol Menthol Mentha
Menthol skeletal.svg
Carvone1 Caraway or Spearmint Caraway, dill,
spearmint
Carvone.svg
Terpineol Lilac Lilac, cajuput
Terpineol alpha.svg
alpha-Ionone Violet, woody Violet
Alpha-ionone-label.png
Thujone Minty Wormwood, lilac,
juniper
Beta-Thujone.svg
Eucalyptol Eucalyptus Eucalyptus
Eucalyptol.png
Jasmone spicy, fruity, floral in dilution Jasmine, Honeysuckle
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
Benzaldehyde.png
Eugenol Clove Clove
Eugenol acsv.svg
Cinnamaldehyde Cinnamon Cassia
Cinnamon
Zimtaldehyd - cinnamaldehyde.svg
Ethyl maltol Cooked fruit
Caramelized sugar
Ethyl maltol.png
Vanillin Vanilla Vanilla
Vanillin.svg
Anisole Anise Anise
Anisol.svg
Anethole Anise Anise
Sweet basil
Anethole-structure-skeletal.svg
Estragole Tarragon Tarragon
Estragole acsv.svg
Thymol Thyme Thyme
Thymol2.svg

Amines

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

Other aroma compounds

Alcohols

Aldehydes

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

Esters

Ketones

Lactones

Thiols

Main page: Chemistry:Thiol
  • 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)[9]
  • (Methylthio)methanethiol (CH3SCH2SH), the "mouse thiol", found in mouse urine and functions as a semiochemical for female mice[10]
  • 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

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.[11]

In mammals, olfactory receptors are expressed on the surface of the olfactory epithelium in the nasal cavity.[5]

Safety and regulation

Patch test

In 2005–06, fragrance mix was the third-most-prevalent allergen in patch tests (11.5%).[12] '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".[13]

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.[14] In the United States, this is because the law regulating cosmetics protects trade secrets.[15]

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.[15] 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.[16]

A 2019 study of the top-selling skin moisturizers found 45% of those marketed as "fragrance-free" contained fragrance.[17]

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.[18]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 El Hadi, Muna; Zhang, Feng-Jie; Wu, Fei-Fei; Zhou, Chun-Hua; Tao, Jun (2013-07-11). "Advances in fruit aroma volatile research". Molecules 18 (7): 8200–8229. doi:10.3390/molecules18078200. ISSN 1420-3049. PMID 23852166. 
  2. ↑ Ulrich, Detlef; Kecke, Steffen; Olbricht, Klaus (2018-03-13). "What do we know about the chemistry of strawberry aroma?". Journal of Agricultural and Food Chemistry 66 (13): 3291–3301. doi:10.1021/acs.jafc.8b01115. ISSN 0021-8561. PMID 29533612. 
  3. ↑ Rothe, M; Specht, M (1976). "[Notes about molecular weights of aroma compounds"]. Nahrung 20 (3): 281–6. doi:10.1002/food.19760200308. PMID 958345. https://pubmed.ncbi.nlm.nih.gov/958345/#:~:text=Abstract,aroma%20effectiveness%20are%20below%20200.. Retrieved 29 September 2020. 
  4. ↑ Fahlbusch, Karl-Georg; Hammerschmidt, Franz-Josef; Panten, Johannes; Pickenhagen, Wilhelm; Schatkowski, Dietmar; Bauer, Kurt; Garbe, Dorothea; Surburg, Horst. "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_141. 
  5. ↑ 5.0 5.1 Haugeneder, Annika; Trinkl, Johanna; Härtl, Katja; Hoffmann, Thomas; Allwood, James William; Schwab, Wilfried (2018-10-26). "Answering biological questions by analysis of the strawberry metabolome". Metabolomics 14 (11): 145. doi:10.1007/s11306-018-1441-x. ISSN 1573-3882. PMID 30830391. 
  6. ↑ Ilc, Tina; Werck-Reichhart, Danièle; Navrot, Nicolas (2016-09-30). "Meta-analysis of the core aroma components of grape and wine aroma". Frontiers in Plant Science 7: 1472. doi:10.3389/fpls.2016.01472. ISSN 1664-462X. PMID 27746799. 
  7. ↑ Gane, S; Georganakis, D; Maniati, K; Vamvakias, M; Ragoussis, N; Skoulakis, EMC; Turin, L (2013). "Molecular-vibration-sensing component in human olfaction". PLOS ONE 8 (1): e55780. doi:10.1371/journal.pone.0055780. PMID 23372854. Bibcode: 2013PLoSO...855780G. 
  8. ↑ 8.0 8.1 Glindemann, D.; Dietrich, A.; Staerk, H.; Kuschk, P. (2005). "The Two Odors of Iron when Touched or Pickled: (Skin) Carbonyl Compounds and Organophosphines". Angewandte Chemie International Edition 45 (42): 7006–7009. doi:10.1002/anie.200602100. PMID 17009284. 
  9. ↑ Block, E. (2010). Garlic and Other Alliums: The Lore and the Science. Royal Society of Chemistry. ISBN 978-0-85404-190-9. 
  10. ↑ Lin, D.Y.; Zhang, S.Z.; Block, E.; Katz, L.C. (2005). "Encoding social signals in the mouse main olfactory bulb". Nature 434 (7032): 470–477. doi:10.1038/nature03414. PMID 15724148. Bibcode: 2005Natur.434..470L. 
  11. ↑ Brattoli, M; Cisternino, E; Dambruoso, PR; de Gennaro, G; Giungato, P; Mazzone, A; Palmisani, J; Tutino, M (5 December 2013). "Gas chromatography analysis with olfactometric detection (GC-O) as a useful methodology for chemical characterization of odorous compounds.". Sensors (Basel, Switzerland) 13 (12): 16759–800. doi:10.3390/s131216759. PMID 24316571. Bibcode: 2013Senso..1316759B. 
  12. ↑ Zug, Kathryn A.; Warshaw, Erin M.; Fowler, Joseph F.; Maibach, Howard I.; Belsito, Donald L.; Pratt, Melanie D.; Sasseville, Denis; Storrs, Frances J. et al. (2009). "Patch-test results of the North American Contact Dermatitis Group 2005-2006". Dermatitis: Contact, Atopic, Occupational, Drug 20 (3): 149–160. ISSN 2162-5220. PMID 19470301. https://pubmed.ncbi.nlm.nih.gov/19470301/. 
  13. ↑ Anne Steinemann, "Fragranced consumer products: exposures and effects from emissions", Air Quality, Atmosphere & Health, December 2016, Volume 9, Issue 8, pp 861–866.
  14. ↑ 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.
  15. ↑ 15.0 15.1 Fragrances in Cosmetics
  16. ↑ Randall Fitzgerald (2006). The Hundred Year Lie. Dutton, 2006. p. 23. ISBN 978-0-525-94951-0. 
  17. ↑ Patti Neighmond (2 October 2017). "'Hypoallergenic' And 'Fragrance-Free' Moisturizer Claims Are Often False". NPR. https://www.npr.org/sections/health-shots/2017/10/02/554365324/hypoallergenic-and-fragrance-free-moisturizer-claims-are-often-false. 
  18. ↑ "IFRA Survey:Transparency List". IFRA. http://www.ifraorg.org/en-us/ingredients#.VH-EkXsdXYg. 



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