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 nameFragranceNatural occurrenceChemical structure
Geranyl acetateFruity,
Floral		Rose
Methyl formateEthereal
Methyl acetateSweet, nail polish
Solvent
Methyl propionate
Methyl propanoate		Sweet, fruity, rum-like
Methyl butyrate
Methyl butanoate		FruityApple
Pineapple
Ethyl acetateSweet, solventWine
Ethyl butyrate
Ethyl butanoate		FruityOrange, Pineapple
Isoamyl acetateFruity, Banana
Pear		Banana plant
Pentyl butyrate
Pentyl butanoate		FruityPear
Apricot
Pentyl pentanoateFruityApple
Octyl acetateFruityOrange
Benzyl acetateFruity, StrawberryStrawberries
Methyl anthranilateFruityGrape
Hexyl acetateFloral, FruityApple, 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.
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.
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.

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. It was estimated to represent about 90% of the world's production volume of fragrances.