Furanocoumarins in citrus fruit

The furocoumarins or furanocoumarins, more commonly known as psoralens, are secondary metabolites commonly found in citrus plants. They are pharmacologic agents and these molecules are allelochemical compounds in plants that have controversial effects on humans, such as phototoxicity and the commonly described interactions with drugs, referred to as the “grapefruit juice effect”.

Citrus plants are able to produce defense compounds such furanocoumarins to cope with herbivorous insects and pathogens. In humans, these chemical compounds are strong photosensitizers and can interact with medications, leading to the “grapefruit juice effect”.

Furanocoumarins can block an enzyme produced by the liver and intestines to break down certain medications in the body. Without this enzymatic activity, levels of these medications can grow to harmful, even toxic, levels.

Citrus peel contains larger diversity and higher concentrations of furanocoumarin than the pulp of the same fruits. Grapefruit is not the only rich in furanocoumarins here. Pomelos (a hybrid between an orange and an Asian fruit called Citrus maxima) also contain furanocoumarins, as do Seville oranges (used in marmalades) and limes. Sweet oranges, such as navel and Valencia, do not contain furanocoumarins.

The major furanocoumarins found in grapefruits include bergamottin, epoxybergamottin, and 6′,7′-dihydroxybergamottin.

Furanocoumarins represent a class of photosensitizers whose use level is likely to be restricted to 1 ppm in cosmetic products by the EU. Furanocoumarins are a therapeutically important subtype and have various clinical applications. They have been used in folk medicine for a long time. The first furanocoumarin, 5-methoxypsoralen, was isolated in 1838 by Kalbrunner from bergamot oil.
Furanocoumarins in citrus fruit