Two months ago, an 11-year-old girl died in Machakos County in Kenya after eating a killer cassava. The cassava also left the girl’s siblings undergoing treatment – but they survived.
Although cassava is one of the tubers promoted in Africa for food security, they also contain hydrogen cyanide which could kill easily.
Left to children who cannot be able to process it to render it safe for consumption, cassava meal can turn leathal.
A staple food for about 700 million people worldwide, this perennial plant is native to South America but was brought to Africa by 17th-century explorers and later introduced to Asia. It thrives in tropical climates.
Scientists say that cassava contains more than one form of cyanogenic glycosides – some natural plant toxins that are present in several plants which are consumed by humans. The lethal cyanide is eventually formed following during crushing of the edible plant material either during consumption or during processing of the food.
Actually, all parts of the cassava plant contain these toxins that helps defend it against pests. The cyanogenic glycosides impart a bitter taste that usually puts off any casual grazers once they have taken the first bite. But the plant also has a backup plan to stop more determined herbivores. The cyanogenic glycosides can be rapidly processed by enzymes within the plant to release lethal hydrogen cyanide. The enzymes and glycosides are separated within the plant cells but if the tissue is damaged, for example by a bite, the two mix and rapidly release the toxic compound. Enzymes within the human gut can also liberate hydrogen cyanide from the cyanogenic glycosides if ingested – and that turns it to a killer!
Cassava is loved because it is very resilient, surviving where many other crops fail, and involves less human investment per calorie than potatoes. It is often poorer communities that rely on cassava for their survival.
Sweet cassava roots contain less than 50 mg per kilogram hydrogen cyanide on fresh weight basis, whereas that of the bitter variety may contain up to 400 mg per kilogram.
Sweet cassava roots can generally be made safe to eat by peeling and thorough cooking. However, bitter cassava roots require more extensive processing. One of the traditional ways to prepare bitter cassava roots is by first peeling and grating the roots, and then prolonged soaking of the gratings in water to allow leaching and fermentation to take place, followed by thorough cooking to release the volatile hydrogen cyanide gas.
Cutting the roots into small pieces, followed by soaking and boiling in water is particularly effective in reducing the cyanide content in cassava. Whilst fresh cassava requires traditional methods to reduce its toxicity, adequately processed cassava flour and cassava-based products have very low cyanide contents and are considered safe to use.
Hydrogen cyanide disrupts the fundamental process of respiration within cells. Without energy, cells die rapidly and on a massive scale, leading to loss of life. Symptoms include vomiting, nausea, headaches and convulsions. Treatment is possible but must begin quickly, before irreversible damage is done.