Grapefruit

• 1. Introduction

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  Grapefruit carries a name that has puzzled people for centuries. A fruit that looks nothing like a grape earned that label sometime in the early 19th century, and nobody can quite agree on why. In 1814, the British naturalist John Lunan published the term, suggesting the name came from the fruit's resemblance in taste to the grape, Vitis vinifera. Others argued the name came from the way the fruit hangs in clusters on the tree, looking from a distance like great yellow bunches of grapes.

  But the naming confusion is only where the strangeness begins. This subtropical citrus was not cultivated on a farm or engineered in a laboratory. It appeared on its own, an accidental crossing of two plants that had traveled from opposite ends of the world to meet on a Caribbean island. Its flesh ranges from pale yellow to deep crimson. Its juice can make certain prescription drugs either dangerously stronger or frustratingly weaker. And for decades, scientists were not even certain what it was.

  Who first documented it, where it truly originated, and why a single glass of its juice can cause a drug overdose are the questions worth sitting with.

• 2. A Caribbean Accident

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  Both ancestors of the grapefruit arrived in the West Indies by 1692. The Indonesian pomelo, Citrus maxima, served as the female parent. The Jamaican sweet orange, Citrus sinensis, itself an ancient hybrid of Asian origin, was the male. Somewhere on those islands, the two plants crossbred without any human assistance.

  One popular story credits a 17th-century trader called Captain Shaddock with bringing pomelo seeds to Jamaica and producing the first fruit, which islanders then called shaddocks. The grapefruit likely arose as a naturally occurring hybrid sometime after both parents had taken root there.

  A hybrid fruit called the forbidden fruit was first documented in 1750 by a Welshman, the Reverend Griffith Hughes, in his work The Natural History of Barbados. Hughes described it alongside fourteen other citrus fruits, including the guiney orange. Whether Hughes's forbidden fruit was the same plant we now call grapefruit remains genuinely unclear.

  In 1830, the Scottish physician and botanist James Macfadyen gave the Jamaican plant the botanical name Citrus paradisi. Macfadyen identified two varieties: one he called forbidden fruit and the other Barbadoes Grape Fruit. He told them apart by shape. The Barbados grapefruit was piriform, meaning pear-shaped. The forbidden fruit was described as maliformis, apple-shaped. A citrus called forbidden fruit or shaddette has since been discovered in Saint Lucia, and it may be the plant Hughes and Macfadyen each described in their own ways.

• 3. Crossing Oceans and Centuries

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  Count Odet Philippe, a French businessman, brought the grapefruit to Florida in 1823, planting it in what is now known as Safety Harbor. The fruit spread through the American Southeast, and by the late 19th century an entrepreneur named Kimball C. Atwood had founded the Atwood Grapefruit Company. The Atwood Grove grew into the largest grapefruit grove in the world, producing 80,000 boxes of fruit each year. Pink grapefruit was discovered there in 1906.

  The name grape-fruit was used during the 19th century to refer not to the fruit we know today but to pomelos, a separate confusion that compounded the botanical muddle. Its true origins were not resolved until the 1940s, when scientists confirmed the hybrid nature of the plant and its official name was adjusted to Citrus paradisi with the addition of a multiplication sign, Citrus x paradisi, marking it unmistakably as a hybrid.

  The grapefruit also became a starting point for further hybridization. Breeders produced the tangelo in 1905, the Minneola tangelo in 1931, and the oroblanco in 1958. In 1993, the Texas Legislature designated a specific grapefruit variety the official State Fruit of Texas, a recognition tied directly to the commercial history of cultivated red varieties.

• 4. Red, Pink, and the Radiation Method

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  The 1929 patent for the Ruby Red, also known as Redblush, marked the beginning of serious commercial success for red grapefruit. The variety came from a chance discovery: a red grapefruit found growing on a pink variety. Its commercial appeal was immediate, but the red color posed a problem. Red tones in grapefruit tend to fade to pink over time.

  To hold the color, breeders turned to radiation. By exposing bud sticks to thermal neutrons, they induced mutations that preserved and deepened the red pigment. The Rio Red variety, registered in Texas in 1984, carries trademarks including Rio Star and Ruby-Sweet and is sometimes promoted under the names Reddest and Texas Choice. Its key improvements are fruit and juice color, both described as deeper red, along with wider adaptation across growing conditions.

  The Star Ruby is the darkest red variety available. It was developed from an irradiated Hudson grapefruit. The Hudson itself was a limb sport of Foster, which was a limb sport of the Walters variety. Despite its striking color, the Star Ruby has found limited commercial success because it is harder to grow than competing varieties.

  White grapefruit varieties follow a parallel history. Named varieties include Duncan, Marsh seedy, and Reed Marsh, among others. The varieties differ mainly in flesh color, with flavors shaped by the balance of sugars dominated by sucrose, organic acids dominated by citric acid, and aromatic compounds including grapefruit mercaptan, a sulfur-containing terpene that gives grapefruit its distinctive smell.

• 5. The Drug Interaction Problem

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  One whole grapefruit or a glass of 200 ml of grapefruit juice is enough to cause drug overdose toxicity in people taking certain medications. The mechanism involves compounds called furanocoumarins, particularly bergamottin and 6',7'-dihydroxybergamottin, which occur in both the flesh and the peel of the fruit.

  Furanocoumarins inhibit CYP3A4, an enzyme belonging to the cytochrome P450 family. That family of enzymes is responsible for metabolizing roughly 90% of all drugs that pass through the human body. When CYP3A4 is suppressed, drugs that rely on it for breakdown stay in the bloodstream longer and at higher concentrations than intended.

  The adverse effects vary by drug but include abnormal heart rhythms, gastrointestinal bleeding, low blood pressure, respiratory depression, rhabdomyolysis, nephrotoxicity, and bone marrow suppression. The interaction runs in both directions. Some drugs need CYP3A4 to become active in the first place. For those drugs, grapefruit suppresses the enzyme and reduces the drug's effect rather than amplifying it.

  A separate mechanism involves grapefruit compounds that inhibit drug absorption in the intestine directly. If a drug is not absorbed from the gut, not enough of it reaches the bloodstream to be therapeutic. Because of these interactions, drugs known to be incompatible with grapefruit are typically marked on their packaging or package insert.

• 6. Food, Cultivation, and Pests

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  Raw white grapefruit is 90% water and provides 138 kJ of food energy per 100 g. It is a rich source of vitamin C, supplying 37% of the daily value in that same 100 g serving. No other micronutrients appear in significant amounts.

  Grapefruit juice contains about half the citric acid of lemon juice but nearly 50% more citric acid than orange juice, placing it in the middle range among common citrus juices. In Costa Rica, particularly in Atenas, cooks often prepare grapefruit with sugar to counteract the sourness, turning it into a sweet. In Haiti, the fruit is known primarily for its juice, called jus de Chadèque, and is also used to make confiture de Chadèque, a jam.

  Grapefruit trees are evergreens that typically reach 4.5 to 6 m in height, though they can grow as tall as 13.7 m. Their leaves are thin, glossy, and dark green, reaching up to 15 cm in length. The white flowers have four or five petals and measure 5 cm across. The fruit is yellow-orange and oblate in shape, ranging from 10 to 15 cm in diameter.

  In the field, grapefruits face several threats. Fruit flies of the family Tephritidae, including Anastrepha suspensa, lay eggs in overripe or spoiled fruit and can cause serious damage in plantations across the Americas. In sub-Saharan Africa, the Citrus swallowtail butterfly, Papilio demodocus, is a minor pest of citrus plantations. Diseases affecting the trees include citrus tristeza virus, citrus canker caused by the bacterium Xanthomonas, and citrus greening disease, which is spread by a psyllid insect and caused by the bacterium Liberibacter.

  In 2023, world production of grapefruits combined with pomelos reached 9.93 million tonnes. China led production with 52% of the total, with Vietnam as a secondary producer.