Control of Konzo and Kits to Determine Cassava Cyanide and Urinary Thiocyanate

Cassava: agriculture, rising African production and cyanogens

Cassava is the third most important food source in the tropics and the staple food of tropical Africa. It originated in Brazil and was introduced into Africa many hundreds of years ago. Its production over 24 African countries has increased threefold from 1980 to 2005 (compared with a 42% increase for Indonesia) and the population in Africa has doubled compared with a 50% increase worldwide (Nhassico et al., 2008). Cassava is a hardy, drought resistant crop that gives acceptable yields on low-fertility soils and is of great importance for subsistence farmers throughout the tropics. In some countries such as Thailand it is also grown in plantations to produce starch and pellets for animal feed, much of which is exported to developed countries.

Cassava roots are very starchy and their protein content is less than that of other tropical root crops such as yam, sweet potato, and taro. Cassava contains the cyanogenic glucoside linamarin and a small amount of lotaustralin (methyl linamarin) both of which are broken down to cyanohydrins and glucose, catalysed by the enzyme linamarase also present in the root. The cyanohydrins readily break down to hydrogen cyanide in neutral or alkaline conditions.

The cassava plant has a large amount of linamarin in the leaves and in the skin of the root. Sweet cassava has a small amount of linamarin in the inner part of the root called the parenchyma and bitter cassava has a much larger amount. The bitter taste is mainly due to linamarin but there are other bitter compounds in the root and also sour constituents, which sometimes confuses the taste buds King and Bradbury, (1995). The total cyanide content of the parenchyma of different cassava varieties ranges from 1 mg HCN equivalents / kg fresh root (1 ppm) to 1550 ppm. In Nigeria one variety is called "chop and die". The parenchyma from sweet cassava is cooked and eaten whereas that from medium and high cyanide cassava must be processed into products such as flour and gari (see Traditional methods of processing cassava roots and leaves). Cassava leaves are used widely in tropical Africa. They are a good source of protein and vitamins but contain large amounts of linamarin that is traditionally removed by pounding followed by boiling in water (see Mild method to remove cyanogens from cassava leaves).

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