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,
Generally, molecules meeting this specification have of less than 310.
Aroma compounds can naturally be found in various , such as fruits and their peels, wine, spices, floral scent, , , and . For example, many form during the ripening of and other crops.[
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An odorizer may add a detectable odor to a dangerous odorless substance, like propane, natural gas, or Hydrogen odorant, as a safety measure.
Aroma compounds classified by structure
Esters
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| Geranyl acetate | Fruity,
Floral | Rose | |
| Methyl formate | Ethereal | | |
| Methyl acetate | Sweet, nail polish
Solvent | | |
Methyl propionate
Methyl propanoate | Sweet, fruity, rum-like | | |
Methyl butyrate
Methyl butanoate | Fruity | Apple
Pineapple | |
| Ethyl acetate | Sweet, solvent | Wine | |
Ethyl butyrate
Ethyl butanoate | Fruity | Orange, Pineapple | |
| Isoamyl acetate | Fruity, Banana,
Pear | Banana plant | |
Pentyl butyrate
Pentyl butanoate | Fruity | Pear
Apricot | |
| Pentyl pentanoate | Fruity | Apple | |
| Octyl acetate | Fruity | Orange | |
| Benzyl acetate | Fruity, Strawberry | Strawberries | |
| Methyl anthranilate | Fruity | Grape | |
| Methyl salicylate | Minty, root beer | Wintergreen | |
| Hexyl acetate | Floral, Fruity | Apple, Plum | |
Linear terpenes
|
| Myrcene | Woody, complex | Verbena, Bay leaf | |
| Geraniol | Rose, flowery | Geranium, Lemon | |
| Nerol | Sweet rose, flowery | Neroli, Lemongrass | |
Citral, lemonal
Geranial, neral | Lemon | Lemon myrtle, Lemongrass | |
| Citronellal | Lemon | Lemongrass | |
| Citronellol | Lemon | Lemongrass, rose
Pelargonium | |
| Linalool | Floral, sweet
Woody | Coriander, Sweet basil, Lavender, Honeysuckle | |
| Nerolidol | Wood, fresh bark | Neroli, ginger
Jasmine | |
| Ocimene | Fruity, Floral | Mango, Curcuma amada | |
Cyclic terpenes
|
| Limonene | Orange | Orange, lemon | |
| Camphor | Camphor | Camphor laurel | |
| Menthol | Menthol | Mentha | |
| Carvone1 | Caraway or Spearmint | Caraway, dill,
spearmint | |
| Terpineol | Lilac | Lilac, cajuput | |
| Ionone | Violet, woody | Violet | |
| Thujone | Minty | Wormwood, lilac,
juniper | |
| Eucalyptol | Eucalyptus | Eucalyptus | |
| Jasmone | spicy, fruity, floral in dilution | Jasmine, Honeysuckle | |
Note: Carvone, depending on its chirality, offers two different smells.
Aromatic
Amines
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.
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Acetaldehyde (ethereal)
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Hexanal (green, grassy)
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cis-3-Hexenal (green )
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Furfural (burnt )
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Hexyl cinnamaldehyde
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Isovaleraldehyde – nutty, fruity, cocoa-like
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Anisic aldehyde – floral, sweet, hawthorn. It is a crucial component of chocolate, vanilla, strawberry, raspberry, apricot, and others.
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Cuminaldehyde (4-propan-2-ylbenzaldehyde) – Spicy, cumin-like, green
Esters
Ketones
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Cyclopentadecanone (musk-ketone)
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Dihydrojasmone (fruity woody floral)
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Oct-1-en-3-one (blood, metallic, mushroom-like)
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2-Acetyl-1-pyrroline (fresh bread, jasmine rice)
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6-Acetyl-2,3,4,5-tetrahydropyridine (fresh bread, tortillas, popcorn)
Lactones
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.
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Allyl thiol (2-propenethiol; allyl mercaptan; CH2=CHCH2SH) (garlic volatiles and garlic breath)
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(Methylthio)methanethiol (CH3SCH2SH), the "mouse thiol", found in mouse urine and functions as a semiochemical for female mice
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Ethanethiol, commonly called ethyl mercaptan (added to propane or other liquefied-petroleum gases used as fuel gases)
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tert-Butylthiol, commonly called tert-butyl mercaptan, is added as a blend of other components to natural gas used as fuel gas.
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Butanethiol, commonly called butyl mercaptan, is a chemical intermediate.
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Grapefruit mercaptan (grapefruit)
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Methanethiol, commonly called methyl mercaptan (after eating asparagus)
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Furan-2-ylmethanethiol, also called furfuryl mercaptan (roasted coffee)
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Benzyl mercaptan (leek or garlic-like)
Miscellaneous compounds
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Methylphosphine and dimethylphosphine (garlic-metallic, two of the most potent odorants known)
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Aroma-compound receptors
Animals that are capable of olfaction 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 , olfactory receptors are gene expression on the surface of the olfactory epithelium in the nasal cavity.[
]
Safety and regulation
In 2005–06, fragrance mix was the third-most-prevalent allergen in (11.5%).[Anne Steinemann, "Fragranced consumer products: exposures and effects from emissions", Air Quality, Atmosphere & Health, December 2016, Volume 9, Issue 8, pp 861–866.]
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.[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.] In the United States, this is because the law regulating cosmetics protects .
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.
A 2019 study of the top-selling 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.
See also
