Papaya

Papaya is a short-lived soft-stemmed plant 3–10 m tall, with a round, spongy, little-branched trunk and white latex in every part. The large leaves, 40–70 cm across, are deeply palmately lobed into 5–7 main lobes and form a spiral cluster at the crown on long hollow petioles. The creamy-white to pale-yellow flowers are fragrant and grow in the leaf axils; the species has several sex forms — male, female and hermaphroditic plants — and individuals can even change sex with the environment. The fruit is a large berry, 15–50 cm long and 0.5–2 kg (large cultivars to 3 kg), with a thin rind that turns from green to yellow-orange at ripening and soft orange to red flesh around a central cavity packed with round black seeds in a clear mucilaginous coat. The plant grows very fast, flowering after only 4–8 months and cropping continuously for 2–3 years.

According to Kew's Plants of the World Online, the native range of Carica papaya runs from southern Mexico to Venezuela (including Belize, Guatemala, Honduras, El Salvador, Nicaragua, Costa Rica, Panama and Colombia), in the humid lowland tropics. Some studies consider the species so long domesticated that truly wild populations are hard to find, with the centre of diversity of the family Caricaceae lying in the Andes (genus Vasconcellea). Today papaya is grown throughout the tropical and subtropical world: India is the largest producer, followed by Brazil, Mexico, Indonesia, Nigeria and Vietnam. In Vietnam it grows everywhere from home gardens to specialised fields in the Mekong Delta, the south-east and the northern plains.

The most distinctive constituents of papaya are the cysteine protease enzymes of the latex, led by papain (EC 3.4.22.2) together with chymopapain, caricain and glycyl endopeptidase; papain breaks down proteins and is therefore used to tenderise meat and debride necrotic tissue. Ripe fruit is rich in carotenoids, especially lycopene (the orange-red pigment) and β-carotene (provitamin A), along with vitamin C and fibre. The leaves contain the alkaloid carpaine and flavonoids; the seeds hold oil and benzyl isothiocyanate with anthelmintic action. A review by Babalola et al. (Scientific African, 2023) purified and characterised five distinct cysteine proteases from papaya leaves, clarifying papain's catalytic mechanism.

Ripe papaya is eaten fresh or made into smoothies, salads and preserves; green papaya is cooked in soups, braised with meat or used in salads. Industrially, papain is a common meat tenderiser and is used to chill-proof beer, process collagen and in cosmetics. In medicine, a papain–urea preparation is used to debride wounds and necrotic ulcers, and chymopapain was formerly injected for chemonucleolysis of herniated discs. Papaya leaf extract has been studied most for dengue: Subenthiran et al. (Evidence-Based Complementary and Alternative Medicine, 2013) showed that papaya leaf juice significantly accelerated the rise in platelet count in patients with dengue fever and dengue haemorrhagic fever; the systematic review and meta-analysis by Charan et al. (International Journal of Applied and Basic Medical Research, 2016) concluded that it supports platelet recovery but that more evidence on clinical significance is needed.

On safety, ripe fruit is generally safe and nutritious, but the latex and green fruit contain papain, which can irritate the skin, trigger allergy (especially in latex-sensitive people) and cause indigestion in large amounts; pregnant women are advised to be cautious with green papaya and leaf extracts because of concerns about uterine contractions. People on anticoagulants or with stomach disease should ask a doctor before using high-dose enzyme preparations. For conservation, the IUCN lists papaya as Least Concern and it is not covered by CITES; however wild populations are threatened by rainforest fragmentation (Chávez-Pesqueira & Núñez-Farfán, American Journal of Botany, 2014), and many relatives in the Andean genus Vasconcellea are rarer still. Conservation focuses on maintaining crop germplasm and protecting the remaining wild populations.