Fragrance compound

Occurrence

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. A 1976 analysis of 2,000 food aroma compounds found a peak in molecular weights around 135–155 and an upper limit near 310, with the most potent compounds all weighing less than 200 Da. A 2003 paper claims the sharp cutoff near 300 Da is instead attributable to the size limitations of olfactory receptors, with higher rates of anosmia for compounds close to this limit such as galaxolide.

Fragrance compounds are found in various foods, such as fruits and their peels, wine, spices, floral scent, perfumes, fragrance oils, and essential oils. For example, many form during the ripening of fruits and other crops. Wines have more than 100 aromas that form as byproducts of fermentation. 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.

History, biochemistry, economics

The technology of fragrances came with the invention of distillation, which allowed to be concentrated and sometimes even separated into individual components. The purification of cinnamaldehyde, the first single component fragrance, marked the beginning of the fragrance and flavor industries. Other single component fragrance compounds that were purified in the 19th century include benzaldehyde, methyl salicylate (oil of wintergreen), and vanillin. Somewhat in step with the synthetic dye industry, the fragrance and flavor industry was established. Many fragrance compounds were prepared synthetically. Spectroscopic methods coupled with various separation techniques allowed the identification of traces of aroma compounds (e.g. in wines, flower extracts, etc.). Tetramethyl acetyloctahydronaphthalenes have been described as "the most successful synthetic fragrance".

The invention of gas chromatography was very important to the development of fragrances. Gas chromatography-olfactometry sometimes involving a human operator sniffing the GC effluent is particularly relevant to the analysis of fragrances. GC-O and related techniques have also been developed to characterize individual enantiomers of chiral aromatic compounds.

Studies on synthetic musk reveal that the odors of some compounds are noticeably affected by deuteration.

Various fragrant fruits are commercially cultivated to have appealing or intensified aromas.

Fragrance compounds classified by chemical structure

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.

Esters

Linear terpenes

Cyclic terpenes

Note: Carvone, depending on its chirality, offers two different smells.

Aromatic

Other aroma compounds

Alcohols

• Furaneol (strawberry)
• 1-Hexanol (herbaceous, woody)
• cis-3-Hexen-1-ol (fresh cut grass)

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 – Spicy, cumin-like, green

Ketones

• Dihydrojasmone (fruity woody floral)
• Oct-1-en-3-one (blood, metallic, mushroom-like)
• 2-Acetyl-1-pyrroline (fresh bread, jasmine rice)
• 6-Acetyl-2,3,4,5-tetrahydropyridine (fresh bread, tortillas, popcorn)
• Diacetyl (butter flavor)
• Acetoin (butter flavor)

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)

Detection and interpretation

Fragrances are detected by the nose when the movement of inspired air contacts olfactory sensory neurons, which in humans, number between 6 and 10 million over a surface area of 2.5 cm² (0.39 sq in) of olfactory epithelium. Fragrance signals are conveyed from the epithelium to the olfactory nerves, and then to the olfactory bulbs, which relay neural impulses about fragrance properties into the primary olfactory cortex of the brain. In the olfactory cortex, fragrance characteristics are integrated to evaluate the safety and appeal of compounds to be ingested, and to recognize environmental and social factors associated by memory with the fragrance.

Safety and regulation

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

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. 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 Product 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 found 45% of those marketed as "fragrance-free" contained fragrance.

Cosmetics are regulated in the United Kingdom and the composition of products must be provided.