Our soils produce many plant species that are known to be useful but remain unexplored and underutilised. One of these plants is the bilimbi (Averrhoa bilimbi L.), a tropical fruit.
It has a lengthy life, evergreen and is widely cultivated in gardens and fields. It is sensitive to cold climate but tolerates evenly distributed rainfall.
However, for it to grow well, there should be two to three months of dry season. The tree grows slowly in shady or semi-shady situations.
Bilimbi needs full sunshine, grows well in rich, moist and well-drained soils. However, the most suitable soils for its growth should be sandy.
The tree can grow to 15 meters high but is usually kept shorter for easy harvesting. Heavy pruning can suppress flowering.
It matures about 50 to 60 days after flowering. It can be propagated through seeds. Seedling trees will fruit in five to six years while well-pruned 10-year-old trees can easily produce about 45kg of fruit per season.
The fruits are picked either individually or in clusters. Bilimbi has a very short shelf-life of up to four to five days when stored in the open. But this can be lengthened if the fruit is chilled or frozen.
Bilimbi plant has not received much horticultural attention, though it is widely cultivated at the Coast. Its trunk is short and divides into a number of branches.
The bilimbi fruit turns bright green when ripe and falls to the ground. Its outer skin is thin, soft and tender and the seeds are flat, wide, smooth and brown.
It is juicy and extremely acidic due to its high oxalic acid content, which is high in the green fruit but decreases in ripe ones.
The oxalic acid content ranges from 10.5 to 14.7mg/g in green fruit and from 8.45 to 10.8mg/g in ripe fruit.
The bilimbi fruit is mainly composed of the pulp, about 86 per cent of the total fruit weight. The fruits contain proteins, lipids, fibre, ash, carbohydrates, thiamine, riboflavin and niacin.
USES OF THE PLANT
They are a dietary source of nitrogen, sodium, potassium, calcium, phosphorous, magnesium, iron, copper, zinc, manganese and selenium.
The fruits are also a rich source of vitamin C and D, antioxidants and are low in fat. Ripe bilimbi fruits have higher vitamin C content than half-ripe ones.
These nutrients are known to have disease-preventing and health-promoting properties.
Bilimbi fruits can be eaten raw or dipped in salt or chili powder as a snack. They are also added in curry or used to add flavour in soup and stew dishes.
The uncooked fruit is prepared as a relish and served with rice and beans or an accompaniment for fish and meat.
Besides acting as flavouring agent in various food dishes, it substitutes tamarind or tomato in most recipes. The fruit can be preserved by sun-drying or processing it into a pickle that has reduced acidity.
To reduce acidity, the fruit is soaked in water overnight, or soaked in salted water for a shorter period. Bilimbi replaces mango in making chutney.
The ripe fruit has been turned into a sweet jam in some Asian regions. Just like in pickle making, the fruit’s acidity is reduced then boiled with much sugar to make jam or even an acid jelly.
Wood from the bilimbi tree is white, soft and even-grained; a rare type available for carpentry. The tree is ornamental; it is commonly grown in gardens in homesteads because of its attractive purple flowers that grow in clusters along the trunk and branches. These flowers attract butterflies, birds and bees.
Bilimbi fruit is too acid to be eaten fresh and is commonly used for pickles, curries, chutney and preserves. It is also made into a refreshing drink similar to lemonade.
Pastes and poultices of the leaves are used for coughs, itches, skin swellings and rheumatism, and fruit conserves or syrups are used for coughs, fevers and inflammation.
At the Coast, bilimbi fruit is referred to as mbilimbi in Swahili. Increased awareness among other communities creates a ready market for farmers and processors of the various products from the fruits and other parts of bilimbi tree.
The writer is based at the Department of Human Nutrition, Egerton University.