Karambola

Averrhoa carambola is a small tree or shrub that grows 5 to 12 m tall, with a bushy shape and a broad, rounded crown. The center of diversity and the original range of the species is tropical Southeast Asia. The tree is cultivated throughout tropical areas of the world.

Explore all seven extraits in the Discovery Set.

The fruit

The flesh is translucent and light yellow to yellow in color. The fruit is about 5-15 cm long and oval. Each fruit can have 10-12 flat, light brown seeds.

Types

There are two main types of carambola: the small sour (or tart) type and the larger sweet type. The sour varieties have a higher oxalic acid content than the sweet type. Ripe, sweet-type carambolas rarely have more than 4% sugar content. They have a tart, sour undertone. The taste has been compared to a mix of apple, pear, grape, and citrus family fruits. Unripe star fruits are firmer and sour, and taste like green apples.

Volatile composition

In a study of fruits grown in Indonesia, Malaysia and Egypt, twenty-four volatiles were detected. Esters were the major class of volatiles in Egyptian fruit, at about 66%, with methyl caproate as the major component. Aldehydes predominated in tropically grown fruits, and the ether myristicin was found exclusively in these. Nonanal, the major straight-chain aliphatic aldehyde, was detected in all fruits at 13.8-33.5%.

Oxalic acid and health

Carambola fruits contain oxalic acid and the neurotoxin caramboxin. Both substances are harmful to individuals suffering from chronic kidney disease, kidney stones, or those under kidney dialysis treatment. Caramboxin is a neurotoxin which is structurally similar to phenylalanine, and is a glutamatergic agonist. Oxalic acid was the major organic acid detected in all the studied fruits, at 1.7-2.7% except in the Malaysian fruit (0.07%). Oxalic acid increases upon fruit ripening. Oxalic acid derivatives such as the butyl propyl and heptyl propyl esters were also detected among the volatiles.

Distribution

Carambolas are cultivated commercially in India, Southeast Asia, southern China, Taiwan, and the southern United States. Carambola is considered to be at risk of becoming an invasive species in many world regions.