Aroma compound

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Fragrance bottles. Perfume shelf 536pix.jpg
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]

Contents

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 nameFragranceNatural occurrenceChemical structure
Geranyl acetate Fruity,
Floral
Rose
Geranyl acetate skeletal.svg
Methyl formate Ethereal
Structural formula of methyl formate.svg
Methyl acetate Sweet, nail polish
Solvent
Methyl-acetate.svg
Methyl propionate
Methyl propanoate
Sweet, fruity, rum-like
Methyl propionate.svg
Methyl butyrate
Methyl butanoate
Fruity Apple
Pineapple
Buttersauremethylester.svg
Ethyl acetate Sweet, solvent Wine
Ethyl acetate2.svg
Ethyl butyrate
Ethyl butanoate
Fruity Orange, Pineapple
Ethyl butyrate2.svg
Isoamyl acetate Fruity, Banana
Pear
Banana plant
Isoamyl acetate.png
Pentyl butyrate
Pentyl butanoate
Fruity Pear
Apricot
Pentyl butyrate.png
Pentyl pentanoate Fruity Apple
Pentyl pentanoate.png
Octyl acetate Fruity Orange
Octyl acetate.svg
Benzyl acetate Fruity, Strawberry Strawberries
Benzyl acetate.png
Methyl anthranilate Fruity Grape
Methyl anthranilate.png
Hexyl acetate Floral, Fruity Apple, Plum
Hexyl acetate.png

Linear terpenes

Compound nameFragranceNatural occurrenceChemical structure
Myrcene Woody, complex Verbena, Bay leaf
Myrcene beta straight acsv.svg
Geraniol Rose, flowery Geranium, Lemon
Geraniol structure.png
Nerol Sweet rose, flowery Neroli, Lemongrass
Nerol2.png
Citral, lemonal
Geranial, neral
Lemon Lemon myrtle, Lemongrass
Geranial structure.png
Citronellal Lemon Lemongrass
Citronellal-2D-skeletal.png
Citronellol Lemon Lemongrass, rose
Pelargonium
Citronellol-2D-skeletal.png
Linalool Floral, sweet
Woody
Coriander, Sweet basil, Lavender, Honeysuckle
Linalool skeletal.svg
Nerolidol Woody, fresh bark Neroli, ginger
Jasmine
Nerolidol.png
Ocimene Fruity, Floral Mango, Curcuma amada
Alpha-ocimene.svg

Cyclic terpenes

Compound nameFragranceNatural occurrenceChemical structure
Limonene Orange Orange, lemon
Limonene-2D-skeletal.svg
Camphor Camphor Camphor laurel
Camphor structure.png
Menthol Menthol Mentha
Menthol skeletal.svg
Carvone 1 Caraway or Spearmint Caraway, dill,
spearmint
Carvone.svg
Terpineol Lilac Lilac, cajuput
Terpineol alpha.svg
alpha-Ionone Violet, woody Violet
Alpha-ionone-label.png
Thujone Minty Wormwood, lilac,
juniper
Beta-Thujone.svg
Eucalyptol Eucalyptus Eucalyptus
Eucalyptol.png
Jasmone spicy, fruity, floral in dilution Jasmine, Honeysuckle
Jasmon structural formation V1.svg

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

Aromatic

Compound nameFragranceNatural occurrenceChemical structure
Benzaldehyde Almond Bitter almond
Benzaldehyde.png
Eugenol Clove Clove
Eugenol acsv.svg
Cinnamaldehyde Cinnamon Cassia
Cinnamon
Zimtaldehyd - cinnamaldehyde.svg
Ethyl maltol Cooked fruit
Caramelized sugar
Ethyl maltol.png
Vanillin Vanilla Vanilla
Vanillin.svg
Anisole Anise Anise
Anisol.svg
Anethole Anise Anise
Sweet basil
Anethole-structure-skeletal.png
Estragole Tarragon Tarragon
Estragole acsv.svg
Thymol Thyme Thyme
Thymol2.svg

Amines

Compound nameFragranceNatural occurrenceChemical structure
Trimethylamine Fishy
Ammonia
Trimethylamine chemical structure.png
Putrescine
Diaminobutane
Rotting fleshRotting flesh
Diaminobutane.png
Cadaverine Rotting fleshRotting flesh
Cadaverine-2D-skeletal.png
Pyridine Fishy Belladonna
Pyridin.svg
Indole Fecal
Flowery
Feces
Jasmine
Indol2.svg
Skatole Fecal Feces
(diluted) Orange Blossoms
Skatole structure.svg

Other aroma compounds

Alcohols

Aldehydes

High concentrations of aldehydes tend to be very pungent and overwhelming, but low concentrations can evoke a wide range of aromas.

Esters

Ketones

Lactones

Thiols

Miscellaneous compounds

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 Epikutanni-test.jpg
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

Related Research Articles

Thiol

A thiol or thiol derivative is any organosulfur compound of the form R−SH, where R represents an alkyl or other organic substituent. The –SH functional group itself is referred to as either a thiol group or a sulfhydryl group, or a sulfanyl group. Thiols are the sulfur analogue of alcohols, and the word is a blend of "thio-" with "alcohol", where the first word deriving from Greek θεῖον (theion) meaning "sulfur".

Perfume Mixture of fragrant substances, usually in liquid form, used to give agreeable scent to objects, air or living creatures

Perfume is a mixture of fragrant essential oils or aroma compounds, fixatives and solvents, usually in liquid form, used to give the human body, animals, food, objects, and living-spaces an agreeable scent.

Vanillin

Vanillin is an organic compound with the molecular formula C8H8O3. It is a phenolic aldehyde. Its functional groups include aldehyde, hydroxyl, and ether. It is the primary component of the extract of the vanilla bean. Synthetic vanillin is now used more often than natural vanilla extract as a flavoring agent in foods, beverages, and pharmaceuticals.

Methanethiol

Methanethiol is an organosulfur compound with the chemical formula CH
3
SH
. It is a colorless gas with a distinctive putrid smell. It is a natural substance found in the blood, brain and feces of animals, as well as in plant tissues. It also occurs naturally in certain foods, such as some nuts and cheese. It is one of the chemical compounds responsible for bad breath and the smell of flatus. Methanethiol is the simplest thiol and is sometimes abbreviated as MeSH. It is very flammable.

Olfactory receptors (ORs), also known as odorant receptors, are expressed in the cell membranes of olfactory receptor neurons and are responsible for the detection of odorants which give rise to the sense of smell. Activated olfactory receptors trigger nerve impulses which transmit information about odor to the brain. These receptors are members of the class A rhodopsin-like family of G protein-coupled receptors (GPCRs). The olfactory receptors form a multigene family consisting of around 800 genes in humans and 1400 genes in mice.

<i>cis</i>-3-Hexen-1-ol

cis-3-Hexen-1-ol, also known as (Z)-3-hexen-1-ol and leaf alcohol, is a colorless oily liquid with an intense grassy-green odor of freshly cut green grass and leaves. It is produced in small amounts by most plants and it acts as an attractant to many predatory insects. cis-3-Hexen-1-ol is a very important aroma compound that is used in fruit and vegetable flavors and in perfumes. The yearly production is about 30 tonnes.

Sotolon

Sotolon is a lactone and an extremely powerful aroma compound, with the typical smell of fenugreek or curry at high concentrations and maple syrup, caramel, or burnt sugar at lower concentrations. Sotolon is the major aroma and flavor component of fenugreek seed and lovage, and is one of several aromatic and flavor components of artificial maple syrup. It is also present in molasses, aged rum, aged sake and white wine, flor sherry, roast tobacco, and dried fruiting bodies of the mushroom Lactarius helvus. Sotolon can pass through the body relatively unchanged, and consumption of foods high in sotolon, such as fenugreek, can impart a maple syrup aroma to one's sweat and urine. In some individuals with the genetic disorder maple syrup urine disease, it is spontaneously produced in their bodies and excreted in their urine, leading to the disease's characteristic smell.

The docking theory of olfaction proposes that the smell of an odorant molecule is due to a range of weak non-covalent interactions between the odorant [a ligand] and its protein odorant receptor, such as electrostatic and Van der Waals interactions as well as H-bonding, dipole attraction, pi-stacking, metal ion, Cation–pi interaction, and hydrophobic effects, in addition to odorant conformation. While this type of recognition has previously been termed the shape theory of olfaction, which primarily considers molecular shape and size, this latter model is oversimplified since two scent molecules may have similar shapes and sizes but different sets of weak intermolecular forces and therefore activate different combinations of odorant receptors. Earlier “lock and key” and "hand in glove" models of protein−ligand binding has been replaced by a more nuanced pictures which consider the distortion of flexible molecules so as to form the optimal interactions with binding partners as in molecular docking of non-olfactory G-protein coupled receptors.

The vibration theory of smell proposes that a molecule's smell character is due to its vibrational frequency in the infrared range. This controversial theory is an alternative to the more widely accepted docking theory of olfaction, which proposes that a molecule's smell character is due to a range of weak non-covalent interactions between its protein odorant receptor, such as electrostatic and Van der Waals interactions as well as H-bonding, dipole attraction, pi-stacking, metal ion, Cation–pi interaction, and hydrophobic effects, in addition to the molecule's conformation.

The odor detection threshold is the lowest concentration of a certain odor compound that is perceivable by the human sense of smell. The threshold of a chemical compound is determined in part by its shape, polarity, partial charges, and molecular mass. The olfactory mechanisms responsible for a compound's different detection threshold is not well understood. As such, odor thresholds cannot be accurately predicted. Rather, they must be measured through extensive tests using human subjects in laboratory settings.

Grapefruit mercaptan is the common name for a natural organic compound found in grapefruit. It is a monoterpenoid that contains a thiol functional group. Structurally a hydroxy group of terpineol is replaced by the thiol in grapefruit mercaptan, so it also called thioterpineol. Volatile thiols typically have very strong, often unpleasant odors that can be detected by humans in very low concentrations. Grapefruit mercaptan has a very potent, but not unpleasant, odor, and it is the chemical constituent primarily responsible for the aroma of grapefruit. This characteristic aroma is a property of only the R enantiomer.

Olfactory fatigue, also known as odor fatigue, olfactory adaptation, and noseblindness, is the temporary, normal inability to distinguish a particular odor after a prolonged exposure to that airborne compound. For example, when entering a restaurant initially the odor of food is often perceived as being very strong, but after time the awareness of the odor normally fades to the point where the smell is not perceptible or is much weaker. After leaving the area of high odor, the sensitivity is restored with time. Anosmia is the permanent loss of the sense of smell, and is different from olfactory fatigue.

Dysosmia is a disorder described as any qualitative alteration or distortion of the perception of smell. Qualitative alterations differ from quantitative alterations, which include anosmia and hyposmia. Dysosmia can be classified as either parosmia or phantosmia. Parosmia is a distortion in the perception of an odorant. Odorants smell different from what one remembers. Phantosmia is the perception of an odor when no odorant is present. The cause of dysosmia still remains a theory. It is typically considered a neurological disorder and clinical associations with the disorder have been made. Most cases are described as idiopathic and the main antecedents related to parosmia are URTIs, head trauma, and nasal and paranasal sinus disease. Dysosmia tends to go away on its own but there are options for treatment for patients that want immediate relief.

OR1A1

Olfactory receptor 1A1 is a protein that in humans is encoded by the OR1A1 gene.

OR2T11

Olfactory receptor 2T11 is a protein that in humans is encoded by the OR2T11 gene.

Foodpairing, or the non-registered trademarked term food pairing, is a method for identifying which foods go well together from a flavor standpoint, while food combining identifies foods that match from a nutritional or digestive standpoint. The method is based on the principle that foods combine well with one another when they share key flavor components. It is a relatively new method that began around the start of the 21st century and is often confused with wine and food matching. By contrast, Foodpairing uses HPLC, gas chromatography and other laboratory methods to analyse food and find chemical components that they have in common.

Aroma of wine

The aromas of wine are more diverse than its flavors. The human tongue is limited to the primary tastes perceived by taste receptors on the tongue – sourness, bitterness, saltiness, sweetness and savoriness. The wide array of fruit, earthy, leathery, floral, herbal, mineral, and woodsy flavor present in wine are derived from aroma notes sensed by the olfactory bulb. In wine tasting, wine is sometimes smelled before being drunk in order to identify some components of the wine that may be present. Different terms are used to describe what is being smelled. The most basic term is aroma which generally refers to a "pleasant" smell as opposed to odor which refers to an unpleasant smell or possible wine fault. The term aroma may be further distinguished from bouquet which generally refers to the smells that arise from the chemical reactions of fermentation and aging of the wine.

Odor Volatilized chemical compounds that humans and animals can perceive by their sense of smell

An odor or odour is caused by one or more volatilized chemical compounds that are generally found in low concentrations that humans and animals can perceive by their sense of smell. An odor is also called a "smell" or a "scent", which can refer to either a pleasant or an unpleasant odor.

Olfaction sense that detects odors

Olfaction, or the sense of smell, is the process of creating the perception of smell. It occurs when an odor binds to a receptor within the nose, transmitting a signal through the olfactory system. Olfaction has many purposes, including detecting hazards, pheromones, and plays a role in taste.

<i>tert</i>-Butylthiol

tert-Butylthiol, also known as 2-methylpropane-2-thiol, 2-methyl-2-propanethiol, tert-butyl mercaptan (TBM), and t-BuSH, is an organosulfur compound with the formula (CH3)3CSH. This thiol is used as an odorant for natural gas, which is otherwise odorless. It may also have been used as a flavoring agent.

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