Citral is an acyclic monoterpene aldehyde. Being a monoterpene, it is made of two isoprene 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; α-citral ) or citral A. The Z-isomer is named neral (cis-citral; β-citral ) or citral B. These stereoisomers occur as a mixture, often not in equal proportions; e.g. in essential oil of Australian ginger, the neral to geranial ratio is 0.61.

Occurrence

Citral is present in the volatile oils of several plants, including lemon myrtle (90–98%), Litsea citrata (90%), Litsea cubeba (70–85%), lemongrass (65–85%), lemon tea-tree (70–80%), Ocimum gratissimum (66.5%), Lindera citriodora (about 65%), Calypranthes parriculata (about 62%), petitgrain (36%), lemon verbena (30–35%), lemon ironbark (26%), lemon balm (11%), lime (6–9%), lemon (2–5%), and orange. 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), is considered superior.

Uses

Citral is a precursor in the industrial production of vitamin A, vitamin E, vitamin K. Citral is also precursor to lycopene, ionone and methylionone.

Fragrances

Citral has a strong lemon (citrus) scent and is used as an aroma compound 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 and insects. 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.