Pomelo

Pomelo is a small tree, usually 5–15 m tall, with thorny young branches and a broad, rounded crown. The simple, alternate leaves are large, ovate to elliptic, 8–20 cm long, and their petioles have broad wings that almost cover the stalk – a feature that separates it from other citrus species. The white, fragrant flowers are 3–7 cm across and grow singly or in clusters of 2–5 in the leaf axils, with 4–5 petals and many stamens. The fruit (a hesperidium) is the largest in the genus Citrus: 15–30 cm across, typically 1–2 kg and sometimes up to 5 kg, with a 1–3 cm thick rind that turns from green to yellow at maturity. Inside are 10–18 segments of juicy, white-pink to red pulp with a few large seeds. It flowers in spring and ripens from late autumn to winter, storing well.

According to Kew's Plants of the World Online, the native range of Citrus maxima runs from Assam (north-east India) to Indo-China, in the wet tropics, as a tree of the rainforest. The species was domesticated very early and is now grown throughout tropical and subtropical Asia, especially in China (Guangxi, Fujian and Zhejiang with cultivars such as Wendan and Shatian), Vietnam, Thailand, Malaysia and Indonesia. From Asia it spread to the Caribbean, Latin America and the Pacific islands, becoming a fruit tree of many tropical regions. In Vietnam, famous growing areas include the Mekong Delta (Nam Roi, Da Xanh), Hanoi (Dien) and Doan Hung in Phu Tho province.

The main bioactive constituents of pomelo are flavonoids and essential oil. Naringin, a bitter flavanone glycoside, is the signature compound and is concentrated in the white albedo and segment membranes, together with its aglycone naringenin and polyphenols such as hesperidin, caffeic acid, p-coumaric acid, ferulic acid and vanillic acid. The outer flavedo is rich in essential oil, with limonene as the dominant monoterpene along with myrcene and sesquiterpenes; nootkatone, a sesquiterpene ketone, contributes the characteristic pomelo aroma. The segments supply vitamin C (about 30–60 mg/100 g), carotenoids and soluble fibre (pectin). These groups were systematised in the review by Sapkota et al. (Evidence-Based Complementary and Alternative Medicine, 2022).

Pomelo is widely eaten fresh and used in juices and salads; the rind is cooked into sweet soups, preserves and candies or used as a marinade, while flowers and leaves yield essential oil. On the research side, the review by Sapkota et al. (2022) reports that naringin has antioxidant, anti-inflammatory, lipid-lowering, anti-atherosclerotic and hepatoprotective effects, and that naringenin shows selective cytotoxicity in some breast-cancer cell lines in preclinical work. A 2023 review of naringin (Molecules) reinforces its antioxidant, anti-inflammatory and metabolic actions. The polyphenols and vitamin C in the segments add antioxidant value, as summarised by a 2024 review in Current Research in Nutrition and Food Science; the rind oil and nootkatone are also used as flavourings and insect repellents.

On safety, naringin in pomelo inhibits the intestinal enzymes CYP3A4 and P-glycoprotein, raising blood levels of certain medicines (statins, some antiarrhythmics, immunosuppressants and some blood-pressure drugs) – the well-documented "grapefruit-juice" interaction – so people on medication should ask their doctor before eating large amounts. Naringin is also bitter and may cause digestive discomfort at high intakes. Concentrated rind oil should not be drunk neat; dilute it and avoid eye contact. For conservation, the IUCN lists pomelo as Least Concern and it is not covered by CITES; nevertheless wild populations in Assam and Southeast Asia are shrinking through forest loss and crossing with cultivated trees, so local cultivars should be maintained in gene-bank collections to prevent genetic erosion.