Star fruit, also known as carambola, is a star shaped tropical fruit with sweet and sour flavour. Carambola is native to Malayan peninsula and cultivated in many parts of Southeast Asia, Pacific islands and China for its fruits. Although abundant and plentiful, carambola is yet to gain popularity, especially in the western world.

Scientific name: Averrhoa carambola. The genus averrhoa includes two well-known sorrel (Oxalidaceae) families of fruiting trees, carambola and bilimbi (tree cucumber).

The fruit is recognized as belimbing manis in many South East Asian regions and kamrakh in India.
 Star fruit is a small, bushy evergreen tree that grows very well under hot, humid, tropical conditions. The plant bears small lilac colour, bell-shaped flowers in clusters, which subsequently develop into oblong shaped fruits with characteristic five angled edges (sides or ribs) that appear like a starfish in cross sections. Both sweet and sour varieties begin to yield under cultivable orchards, and ready for harvesting when the plants reach about 3-4 years old.

Carambola fruit features light-green to yellow with attractive smooth waxy surface and weighs about 70-130g. Inside, its crispy, juicy pulp can either be mildly sweet or extremely sour depending upon the cultivar type and amount of oxalic acid concentration. In some seed types, 2-5 tiny edible seeds found at the centre of each angled cavity.

Health benefits

Star fruit is one of the very low calorie exotic fruits. 100 g fruit just provides 31 calories, which is much lower than for any other popular tropical fruits. Nonetheless, it has an impressive list of essential nutrients, antioxidants, and vitamins required for well-being.

The fruit along with its waxy peel provides a good amount of dietary fibre. Fibre helps prevent absorption of dietary LDL cholesterol in the gut. The dietary fibres also help protect the mucous membrane of the colon from exposure to toxic substances by binding to cancer-causing chemicals in the colon.

Star fruit contains good quantities of vitamin-C. Vitamin C is a powerful natural antioxidant. 100 g of fresh fruit provides 34.7 mg or 57% of daily-required levels of vitamin C. In general, consumption of fruits rich in vitamin C helps the human body develop resistance against infectious agents and scavenge harmful, pro-inflammatory free radicals from the body.

Star fruit is rich in antioxidant phyto-nutrients polyphenolic flavonoids. Some of the important flavonoids are quercetin, epicatechin, and gallic acid. Total polyphenol contents (Folin assay) in this fruit are143 mg/100 g. These compounds help protect from deleterious effects of oxygen derived free radicals by warding them off the body.

In addition, the fruit is a good source of B-complex vitamins such as folates, riboflavin, and pyridoxine (vitamin B-6). Together, these vitamins help as co-factors for enzymes in metabolism as well as in various synthetic functions inside the body.

It also contains small amount of minerals and electrolytes like potassium, phosphorus, and zinc and iron. Potassium is an important component of cell and body fluids helps controlling heart rate and blood pressure; thus, counters bad influences of sodium.

Antioxidant activity: The strong correlation was shown between the antioxidant activity and total phenolics and proanthocyanidins contents. Fewer amounts of flavonoids are found in the fruit whereas the correlation between antioxidant activity and ascorbate content was found poor. Carambola possesses huge phenolic antioxidants that provide health benefits. The huge presence of phenolics and antioxidant activity provides various benefits to the health when it is used in functional food products.

Anti-microbial and antifungal activity: The extract of ethanol, butanol fractions, ethyl acetate, hexane and flavonoids such as fucopyranoside from the leaves of carambola is used for the purpose of anti-inflammatory. The extract of ethanol lowered edema when it is taken in dose dependent manner. The ethanol extract also prevented the Myeloperoxidase activity.

Antitumor activity: The study conducted on the cultured cells of Carambola concluded that it has possessed the ability to hydroxylate sesquiterpene compounds in a region and steroselective manner. The research was made on the brain tumour cells with the alcoholic extract from the carambola stems but the leaves extract was efficient against the liver carcinoma cells.

Antiulcer activity: The water alcohol extract of the leaves of Carambola was examined about the potential of anti-ulcerogenic. When the research was conducted on rats, it does not showed the indomethacin and acute stress ulcerogenic models which shows that the presence of ethanolic extract of Carambola possess lower anti-ulcer activity.

Hypotensive activity: The hypotensive effect was studied on the isolated rat aorta with the aqueous extract. It reduces the induced contractions and contractile mechanisms. The conclusion derived from the aqueous extract shows its hypotensive nature.

Nephrotoxic effect: The study about the effects of Carambola on the patients of renal failure shows that the fruit and its juice may urge neurotoxicity and nephrotoxicity. The patients of chronic disease should avoid carambola. Those having normal renal function should also avoid the consumption of fruit or juice on an empty stomach.

Analgesic: The study which was conducted on the analgesic activity of the Carambola fruit shows that it shows the significant central and peripheral analgesic activities in acetic acid.

Hypoglycaemic: The pulp of ripe Carambola possesses the hypoglycaemic effect which reduces the levels of blood glucose. The report shows that the dietary fibres, alcohol insoluble solid and water insoluble solid segregated from the pomace of Carambola acquire the hypoglycaemic effects.

Anthelmintic: Carambola leaves showed an anthelmintic activity in dose dependent manner which shows the time of paralysis in 10 minutes and the death in 16 minutes in 100 mg/ml concentration.

Hypocholesterolaemic & Hypolipidemic activity

The report on an isolated water-insoluble fibre rich fraction (WIFF) in the star fruit pomace shows the hypolipidamemic and hypocholesterolaemic activity. It reduces the cholesterol and lipid by promoting the extraction of cholesterol and bile acids. It reduces the triglycerol in serum, liver cholesterol and raises the cholesterol, total lipids and bile acids.