Aroma compound

Fragrance bottles.

An aroma compound, also known as an odorant, aroma, fragrance 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,^[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 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
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
Hexyl acetate	Floral, Fruity	Apple, Plum

Linear terpenes[]

Compound name	Fragrance	Natural occurrence	Chemical structure
Myrcene	Woody, complex	Verbena, Bay leaf
Geraniol	Rose, flowery	Geranium, Lemon
Nerol	, 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	Woody, fresh bark	Neroli, ginger Jasmine
Ocimene	Fruity, Floral	Mango, Curcuma amada

Cyclic terpenes[]

Compound name	Fragrance	Natural occurrence	Chemical structure
Limonene	Orange	Orange, lemon
Camphor	Camphor	Camphor laurel
Menthol	Menthol	Mentha
Carvone1	Caraway or Spearmint	Caraway, dill, spearmint
Terpineol	Lilac	Lilac, cajuput
alpha-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[]

Compound name	Fragrance	Natural occurrence	Chemical structure
Benzaldehyde	Almond	Bitter almond
Eugenol	Clove	Clove
Cinnamaldehyde	Cinnamon	Cassia Cinnamon
Ethyl maltol	Cooked fruit Caramelized sugar
Vanillin	Vanilla	Vanilla
Anisole	Anise	Anise
Anethole	Anise	Anise Sweet basil
Estragole	Tarragon	Tarragon
Thymol	Thyme	Thyme

Amines[]

Compound name	Fragrance	Natural occurrence	Chemical structure
Trimethylamine	Fishy Ammonia
Putrescine Diaminobutane	Rotting flesh	Rotting flesh
Cadaverine	Rotting flesh	Rotting flesh
Pyridine	Fishy	Belladonna
Indole	Fecal Flowery	Feces Jasmine
Skatole	Fecal	Feces (diluted) Orange Blossoms

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)
• (Gardenia)

Ketones[]

• Cyclopentadecanone (musk-ketone)^[7]
• Dihydrojasmone (fruity woody floral)
• Oct-1-en-3-one (blood, metallic, mushroom-like)^[8]
• 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[]

• 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[]

• Methylphosphine and dimethylphosphine (garlic-metallic, two of the most potent odorants known)^[8]
• 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.^[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. 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".^[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[]

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

References[]