Aroma compound
An aroma compound, also known as an odorant, aroma, fragrance, or flavor, is a chemical compound that has a smell or odor. For a chemical compound to have a smell or odor it must be sufficiently volatile to be transported to the olfactory system in the upper part of the nose.
Generally molecules meeting this specification have molecular weights of less than 300. Flavors affect both the sense of taste and smell, whereas fragrances affect only smell. Flavors tend to be naturally occurring, and fragrances tend to be synthetic.
Aroma compounds can be found in food, wine, spices, floral scent, perfumes, fragrance oils, and essential oils. For example, many form biochemically during the ripening of fruits and other crops. In wines, most form as byproducts of fermentation. Also, many of the aroma compounds play a significant role in the production of flavorants, which are used in the food service industry to flavor, improve, and generally increase the appeal of their products.
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
Cyclic terpenes
Note: Carvone, depending on its chirality, offers two different smells.Aromatic
Amines
Other aroma compounds
Alcohols
High concentrations of aldehydes tend to be very pungent and overwhelming, but low concentrations can evoke a wide range of aromas.- Acetaldehyde
- Hexanal
- cis-3-Hexenal
- Furfural
- 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 – Spicy, cumin-like, green
Esters
- Fructone
- Ethyl methylphenylglycidate
- alpha-Methylbenzyl acetate
Ketones
- Cyclopentadecanone
- Dihydrojasmone
- Oct-1-en-3-one
- 2-Acetyl-1-pyrroline
- 6-Acetyl-2,3,4,5-tetrahydropyridine
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
Thiols
- Thioacetone 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
- methanethiol, the "mouse thiol", found in mouse urine and functions as a semiochemical for female mice
- Ethanethiol, commonly called ethyl mercaptan
- 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
- Methanethiol, commonly called methyl mercaptan
- Furan-2-ylmethanethiol, also called furfuryl mercaptan
- Benzyl mercaptan
Miscellaneous compounds
- Methylphosphine and dimethylphosphine
- Phosphine
- Diacetyl
- Acetoin
- Nerolin
- Tetrahydrothiophene
- 2,4,6-Trichloroanisole
- Substituted pyrazines
Aroma-compound receptors
In mammals, olfactory receptors are expressed 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 patch tests. '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".The composition of fragrances is usually not disclosed in the label of 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.
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. 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.
A 2019 study of the top-selling skin moisturizers from amazon.com, Target, and Walmart found 45% of those marketed as "fragrance-free" contained fragrance.