Afragrance compound (or fragrance) is achemical compound with a pleasantodor. Fragrances affect only thesense of smell, whereas flavors can affect both the sense oftaste and smell. Fragrances are often mixtures of individual fragrance compounds. Although many fragrances are derived from natural sources, many are synthetic. Fragrances are widely used incosmetics and are the basis for a large industry.[2]
Stench compounds have unpleasant odors. Some are used asodorizer or an odorant usually have an intense odor, which may be pleasant or not. They are sometimes used to confer a detectable odor to an odorless substance, likepropane,natural gas, orhydrogen, as a safety measure.[3]
For an individual chemical or class of chemical compounds to impart a smell or fragrance, it must be sufficientlyvolatile for transmission via the air to theolfactory system in the upper part of the nose. Generally, fragrance compounds havemolecular weights of less than 310.[4]
Fragrance compounds are found in variousfoods, such as fruits and theirpeels,wine,spices,floral scent,perfumes,fragrance oils, andessential oils. For example, many form during theripening offruits and other crops.[5] Wines have more than 100 aromas that form as byproducts offermentation.[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.[2]
The technology of fragrances came with the invention ofdistillation, which allowed to be concentrated and sometimes even separated into individual components. The purification ofcinnamaldehyde, 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 includebenzaldehyde,methyl salicylate (oil of wintergreen), andvanillin. Somewhat in step with the syntheticdye 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).[2] Another relevant invention isgas chromatography, especially when coupled to detection by humans, i.e.gas chromatography-olfactometry. Techniques were also developed to characterize and synthesize individual enantiomers of chiral aromatic compounds.[7]
Animals, by the process ofolfaction, detect aromas usingolfactory receptors located on the surface of the olfactory epithelium in thenasal cavity.[5] Of commercial importance, aroma compounds are identified bygas chromatography, sometimes coupled to olfactometry, which involves a human operator sniffing the GC effluent.[8] Studies oncyclopentadecanone ("musk-ketone") reveal that the odors of some compounds are noticeably affected bydeuteration.[9]
Various fragrant fruits arecommercially cultivated to have appealing or intensified aromas.[10]
In 2010, theInternational 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.[11][12]
| Compound name | Fragrance | Natural occurrence | Chemical structure |
|---|---|---|---|
| Geranyl acetate | Fruity, Floral | Rose |  |
| Methyl formate | Ethereal | synthetic |  |
| Methyl acetate | Sweet, nail polish Solvent | synthetic |  |
| Fructone | fruity, apple-like | synthetic |  |
| Ethyl methylphenylglycidate | Strawberry | synthetic |  |
| Methyl propionate | Sweet, fruity,rum-like |  | |
| Methyl butyrate | Fruity | Apple Pineapple |  |
| Ethyl acetate | Sweet, solvent | Wine |  |
| Ethyl butyrate | Fruity | Orange,Pineapple |  |
| Isoamyl acetate | Fruity,Banana, Pear | Banana plant |  |
| Pentyl butyrate | 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 |  |
| Compound name | Fragrance | Natural occurrence | Chemical structure |
|---|---|---|---|
| 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 | Woody, fresh bark | Neroli,ginger Jasmine |  |
| Ocimene | Fruity, Floral | Mango,Curcuma amada |  |
| Compound name | Fragrance | Natural occurrence | Chemical structure |
|---|---|---|---|
| Limonene | Orange | Orange,lemon |  |
| Camphor | Camphor | Camphor laurel |  |
| Menthol | Menthol | Mentha |  |
| Carvone1 | Caraway orSpearmint | 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.
| 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 |  |
High concentrations of aldehydes tend to be very pungent and overwhelming, but low concentrations can evoke a wide range of aromas.
Fragrances are detected by the nose when the movement of inspired air contactsolfactory sensory neurons, which in humans, number between 6 and 10 million over asurface area of 2.5 cm2 (0.39 sq in) ofolfactory epithelium.[14] Fragrance signals are conveyed from the epithelium to theolfactory nerves, and then to theolfactory bulbs, which relay neural impulses about fragrance properties into theprimary olfactory cortex of the brain.[14] 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.[14][15]
In 2005–06, fragrance mix was the third-most-prevalentallergen inpatch tests (11.5%).[16] 'Fragrance' was votedAllergen 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".[17]
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.[18] In the United States, this is because the law regulating cosmetics protectstrade secrets.[19]
In the United States, fragrances are regulated by theFood and Drug Administration if present in cosmetics or drugs, by theConsumer Product Safety Commission if present in consumer products.[19] No pre-market approval is required, except for drugs. Fragrances are also generally regulated by theToxic 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 theEPA. The EPA, however, does not conduct independent safety testing but relies on data provided by the manufacturer.[20]
A 2019 study of the top-sellingskin moisturizers found 45% of those marketed as "fragrance-free" contained fragrance.[21]
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