The grapefruit is a subtropical citrus tree known for its relatively large sour to semi-sweet, somewhat bitter fruit. Grapefruit is a citrus hybrid originating in Barbados as an accidental cross between the sweet orange (C. sinensis) and pomelo (or shaddock) (C. maxima), both of which were introduced from Asia in the seventeenth century. When found, it was nicknamed the "forbidden fruit". Frequently, it is misidentified as the very similar parent species, pomelo.
The evergreen grapefruit trees usually grow to around 5–6 meters (16–20 ft) tall, although they may reach 13–15 m (43–49 ft). The leaves are glossy, dark green, long (up to 15 centimeters (5.9 in)), and thin. It produces 5 cm (2 in) white four-petaled flowers. The fruit is yellow-orange skinned and generally, an oblate spheroid in shape; it ranges in diameter from 10–15 cm (3.9–5.9 in). The flesh is segmented and acidic, varying in color depending on the cultivars, which include white, pink, and red pulps of varying sweetness (generally, the redder varieties are the sweetest). The 1929 U.S. Ruby Red (of the Redblush variety) has the first grapefruit patent.
The grapefruit was brought to Florida by Count Odet Philippe in 1823 in what is now known as Safety Harbor. Further crosses have produced the tangelo (1905), the Minneola tangelo (1931), and the oroblanco (1984).
An early pioneer in the American citrus industry was Kimball Atwood, a wealthy entrepreneur who founded the Atwood Grapefruit Company in the late nineteenth century. The Atwood Grove became the largest grapefruit grove in the world, with a yearly output of 80,000 boxes of fruit. It was there that pink grapefruit was first discovered in 1906.
Grapefruit varieties are differentiated by the flesh color of fruit they produce. Common varieties are red, white, and pink pulp colors. Flavors range from highly acidic and somewhat sour to sweet and tart, resulting from composition of sugars (mainly sucrose), organic acids (mainly citric acid), and monoterpenes and sesquiterpenes providing aromas.
This happens in two very different ways. In the first, the effect is from bergamottin, a natural furanocoumarin in both grapefruit flesh and peel that inhibits the CYP3A4 enzyme, (among others from the P450 enzyme family responsible for metabolizing 90% of drugs). The action of the CYP3A4 enzyme itself is to metabolize many medications. If the drug's breakdown for removal is lessened, then the level of the drug in the blood may become too high or stay too long, leading to adverse effects. On the other hand, some drugs must be broken down to become active, and inhibiting CYP3A4 may lead to reduced drug effects.
Grapefruits are one of the most common hosts for fruit flies like A. suspensa, which will lay their eggs in overripe or spoiled grapefruits. The larvae of these flies will then consume the fruit in order to gain nutrients until they can proceed into the pupae stage. This parasitism has led to millions in economic costs for nations in Central America and Southern North America.