Soursop

Botanical description

Annona muricata is a small, upright, evergreen tree that can grow to about 10 m (33 ft) tall.

Its young branches are hairy. The leaves are oblong to oval, 8 to 16 cm (3.1 to 6.3 in) long and 3 to 7 cm (1.2 to 2.8 in) wide. They are a glossy dark green with no hairs above, and paler and minutely hairy to no hairs below. The leaf stalks are 4 to 13 mm (0.16 to 0.51 in) long and without hairs.

Flower stalks (peduncles) are 2 to 5 mm (0.079 to 0.197 in) long and woody. They appear opposite from the leaves or as an extra from near the leaf stalk, each with one or two flowers, occasionally a third. Stalks for the individual flowers (pedicels) are stout and woody, minutely hairy to hairless and 15 to 20 mm (0.59 to 0.79 in) with small bractlets nearer to the base which are densely hairy.

The petals are thick and yellowish. Outer petals meet at the edges without overlapping and are broadly ovate, 2.8 to 3.3 cm (1.1 to 1.3 in) by 2.1 to 2.5 cm (0.83 to 0.98 in), tapering to a point with a heart shaped base. They are evenly thick, and are covered with long, slender, soft hairs externally and matted finely with soft hairs within. Inner petals are oval shaped and overlap. They measure roughly 2.5 to 2.8 cm (0.98 to 1.10 in) by 2 cm (0.79 in), and are sharply angled and tapering at the base. Margins are comparatively thin, with fine matted soft hairs on both sides. The receptacle is conical and hairy. The stamens are 4.5 mm (0.18 in) long and narrowly wedge-shaped. The connective-tip terminate abruptly and anther hollows are unequal. Sepals are quite thick and do not overlap. Carpels are linear and basally growing from one base. The ovaries are covered with dense reddish brown hairs, 1-ovuled, style short and stigma truncate. Its pollen is shed as permanent tetrads.

The fruit is oval, dark green when immature, with a leathery, inedible skin that turns yellow-green during maturity. They grow to 10–35 cm (3.9–13.8 in) long, with a moderately firm texture, and typically weigh around 4 kg (8.8 lb), up to a maximum of 10 kg (22 lb). Their flesh is juicy, acidic, whitish, and aromatic somewhat like pineapple, although with a unique earthy aroma. Most of the immature segments are seedless, whereas mature fruit may contain as many as 200 seeds.

Distribution

Annona muricata is tolerant of poor soil and prefers lowland areas between the altitudes of 0 to 1,200 m (3,900 ft). The exact origin is unknown; it is native to the tropical regions of the continental Americas and is widely propagated. It is an introduced species on all temperate continents, especially in subtropical regions.

Cultivation

The plant is grown for its 10–35 cm (3.9–13.8 in) long, prickly, green fruit, which can weigh up to 10 kg (22 lb), making it the largest Annona fruit, though not as large as the related junglesop Anonidium mannii. Away from its native area, some limited production occurs as far north as southern Florida within USDA Zone 10; however, these are mostly garden plantings for local consumption. It is also grown in parts of China and Southeast Asia and is abundant on the Island of Mauritius. The main suppliers of the fruit are Mexico followed by Peru, Brazil, Ecuador, Guatemala, and Haiti. To aid soursop breeders and stimulate further development of genomic resources for this globally important plant family, the complete genome for Annona muricata was sequenced in 2021.

Uses

Culinary

The flesh of the fruit consists of an edible, white pulp, some fiber, and a core of indigestible black seeds. The pulp is also used to make fruit nectar, smoothies, fruit juice drinks, as well as candies, sorbets, and ice cream flavorings.

Nutrition

Raw soursop is 81% water, 17% carbohydrates, 1% protein, and has negligible fat (see table). In a reference amount of 100 g (3.5 oz), the raw fruit supplies 276 kilojoules (66 kilocalories) of food energy, and contains only vitamin C as a significant amount (23%) of the Daily Value, with no other micronutrients in appreciable amounts (table).

Phytochemicals

The neurotoxin annonacin is contained in the fruit, seeds, and leaves of soursop. The leaves of Annona muricata contain annonamine, which is an aporphine-class alkaloid containing a quaternary ammonium group. The plant also contains lichexanthone, a compound in the xanthone class.

Neurotoxicity

The Memorial Sloan-Kettering Cancer Center cautions, "alkaloids extracted from graviola may cause neuronal dysfunction". Annonacin has been shown in laboratory research to be neurotoxic. In 2010, the French food safety agency concluded that "it is not possible to confirm that the observed cases of atypical Parkinson syndrome ... are linked to the consumption of Annona muricata".

Controversy

In 2008, the Federal Trade Commission in the United States stated that use of soursop to treat cancer was "bogus", and there was "no credible scientific evidence" that the extract of soursop sold by Bioque Technologies "can prevent, cure, or treat cancer of any kind." Also in 2008, a UK court case relating to the sale of Triamazon, a soursop product, resulted in the criminal conviction of a man under the terms of the UK Cancer Act for offering to treat people for cancer. A spokesman for the council that instigated the action stated, "it is as important now as it ever was that people are protected from those peddling unproven products with spurious claims as to their effects."

The Memorial Sloan-Kettering Cancer Center and Cancer Research UK state that cancer treatment using soursop is not supported by reliable clinical evidence. According to Cancer Research UK, "Many sites on the internet advertise and promote graviola capsules as a cancer cure, but none of them are supported by any reputable scientific cancer organizations" and "there is no evidence to show that graviola works as a cure for cancer".