Citrus is one of the most economically important genera of edible fruits, including the sweet and bitter oranges, lemon, lime, citron, bergamot, grapefruit, and tangerine or mandarin. Many of these plants, including the bitter orange, originated as hybrids among only a few pure species. Bitter orange is found only in cultivation; it has been well known in warm regions of Asia and the Middle East for more than a thousand years. It is used primarily for production of marmalade and essential oil, and as a rootstock for the vegetative propagation of other cultivated citrus. Like other citrus plants, it is a tree whose evergreen leaves contain numerous translucent essential oil glands. The fruit, similar to a berry, is technically called a hesperidium. The outer layer of the peel contains the essential oil glands that provide much of its flavor; the juicy, edible part of the fruit is composed of fleshy trichomes (?hairs?) inside the ovary.

Medicinal uses of citrus are limited, although orange peel is an ingredient in herbal formulas used in Traditional Chinese Medicine. The antioxidant flavonoids contained in citrus peel or juice may help to prevent cancer and improve cardiovascular health. Extracts or isolated flavonoids from bitter orange have recently been shown in animal studies to reduce bone marrow and kidney damage caused by toxic compounds, although use in humans has not been tested. The peel of bitter orange, and thus products made from it such as marmalade, also contain synephrine, an alkaloid that has a stimulant effect. Bitter orange has therefore been marketed as a dietary supplement alleged to increase metabolism and cause weight loss. It has also been targeted for a legal ban by activists who fear that, like ephedrine-containing products, it might cause serious side effects in susceptible consumers. There is no substantial evidence that bitter orange supplements are either useful or dangerous. Grapefruit juice is well known to interact with many pharmaceuticals, increasing their blood levels so that an otherwise normal dose can result in increased toxicity. Other citrus juices do not interact so strongly with drugs as a rule, but their effects may be variable; bitter orange juice has been shown to significantly increase blood levels of a few drugs.

Selected References

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Ortiz, J. M. 2002. Botany: taxonomy, morphology and physiology of fruits, leaves and flowers. Pp. 16-35 in: Dugo, G., and A. Di Giacomo, eds. Citrus. The genus Citrus. Medicinal and Aromatic Plants ? Industrial Profiles, vol. 4. Taylor & Francis: London and New York.

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