Citral is an acyclic monoterpene aldehyde, and being a monoterpene, it is made of two
isoprene
Isoprene, or 2-methyl-1,3-butadiene, is a common volatile organic compound with the formula CH2=C(CH3)−CH=CH2. In its pure form it is a colorless volatile liquid. Isoprene is an unsaturated hydrocarbon. It is produced by many plants and animals ...
units. Citral is a collective term which covers two geometric isomers that have their own separate names; the ''E''-isomer is named geranial (''trans''-citral) or citral A. The ''Z''-isomer is named neral (''cis''-citral) or citral B. These stereoisomers occur as a mixture, not necessarily
racemic
In chemistry, a racemic mixture, or racemate (), is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as racemates. ...
; e.g. in essential oil of Australian ginger, the neral to geranial ratio is 0.61.
Occurrence
Citral is present in the oils of several plants, including lemon myrtle (90–98%), ''
Litsea citrata
''Litsea'' is a genus of evergreen or deciduous trees or shrubs belonging to the laurel family, Lauraceae. The genus includes a large number of accepted species in tropical and subtropical areas of North America and Asia.
Characteristics
They a ...
'' (90%), ''
Litsea cubeba
''Litsea cubeba'', the aromatic litsea or may chang, is an evergreen tree or shrub 5–12 meters high in the family Lauraceae. It is native to Southern Chinese region including Sichuan, Guizhou, Yunnan, Taiwan and Fujian, and Southeast Asian co ...
lemon balm
Lemon balm (''Melissa officinalis'') is a perennial herbaceous plant in the mint family and native to south-central Europe, the Mediterranean Basin, Iran, and Central Asia, but now naturalised elsewhere.
It grows to a maximum height of . The ...
lemon
The lemon (''Citrus limon'') is a species of small evergreen trees in the flowering plant family Rutaceae, native to Asia, primarily Northeast India (Assam), Northern Myanmar or China.
The tree's ellipsoidal yellow fruit is used for culin ...
(2–5%), and
orange
Orange most often refers to:
*Orange (fruit), the fruit of the tree species '' Citrus'' × ''sinensis''
** Orange blossom, its fragrant flower
* Orange (colour), from the color of an orange, occurs between red and yellow in the visible spectrum ...
. Further, in the lipid fraction (essential oil) of Australian ginger (51-71%) Of the many sources of citral, the Australian myrtaceous tree, Lemon Myrtle, Backhousia citriodora F. Muell. (of the family
Myrtaceae
Myrtaceae, the myrtle family, is a family of dicotyledonous plants placed within the order Myrtales. Myrtle, pōhutukawa, bay rum tree, clove, guava, acca (feijoa), allspice, and eucalyptus are some notable members of this group. All spe ...
), is considered superior.
Uses
Citral has a strong lemon (citrus) scent and is used as an
aroma compound
An aroma compound, also known as an odorant, aroma, fragrance or flavoring, 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 vo ...
in perfumery. It is used to fortify lemon oil. (Nerol, another perfumery compound, has a less intense but sweeter lemon note.) The aldehydes citronellal and citral are considered key components responsible for the lemon note with citral preferred.
It also has pheromonal effects in
acari
Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear ...
and
insects
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs ...
.
Citral is used in the synthesis of
vitamin A
Vitamin A is a fat-soluble vitamin and an essential nutrient for humans. It is a group of organic compounds that includes retinol, retinal (also known as retinaldehyde), retinoic acid, and several provitamin A carotenoids (most notably ...
,
lycopene
Lycopene is an organic compound classified as a tetraterpene and a carotene. Lycopene (from the neo-Latin '' Lycopersicum'', the tomato species) is a bright red carotenoid hydrocarbon found in tomatoes and other red fruits and vegetables.
Occ ...
, ionone, and methylionone, to mask the smell of smoke.
The herb Cymbopogon citratus has shown promising insecticidal and antifungal activity against storage pests.
Food additive
Citral is commonly used as a food additive ingredient.
It has been tested (2016) in vitro against the food-borne pathogen Cronobacter sakazakii.
Medical exploration
In a report (1997), Citral is mentioned as cytotoxic to P(388) mouse leukaemia cells.
It has 'strong'
antimicrobial
An antimicrobial is an agent that kills microorganisms or stops their growth. Antimicrobial medicines can be grouped according to the microorganisms they act primarily against. For example, antibiotics are used against bacteria, and antifungals ...
qualities.
Adverse effects
Two studies showed 1–1.7% of people to be allergic to citral, with allergies frequently reported. Citral on its own is strongly sensitizing to allergies; the International Fragrance Association recommends that citral only be used in association with substances that prevent a sensitizing effect. Citral has been extensively tested, with no known genotoxicity or
carcinogenic
A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive sub ...
effect.
See also
*
Citronellal
Citronellal or rhodinal ( C10 H18 O) is a mono terpenoid aldehyde, the main component in the mixture of terpenoid chemical compounds that give citronella oil its distinctive lemon scent.
Citronellal is a main isolate in distilled oils from the ...
*
Geraniol
Geraniol is a monoterpenoid and an alcohol. It is the primary component of citronella oil and is a primary component of rose oil, palmarosa oil. It is a colorless oil, although commercial samples can appear yellow. It has low solubility in w ...
*
Limonene
Limonene is a colorless liquid aliphatic hydrocarbon classified as a cyclic monoterpene, and is the major component in the oil of citrus fruit peels. The -isomer, occurring more commonly in nature as the fragrance of oranges, is a flavoring ...