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close this bookTraditional Storage of Yams and Cassave and its Improvement (GTZ)
close this folder5 Cassava
close this folder5.6 The processing of cassava roots
View the document5.6.1 The purpose of processing
View the document5.6.2 Hydrogen cyanide and its release
View the document5.6.3 The production of cassava chips

5.6.2 Hydrogen cyanide and its release

Cassava roots contain hydrogen cyanide (HCN) which is a very strong poison. The lethal dose for an adult is approx. 60 mg per day (HAHN, 1989). Due to the high content of HCN, an unbalanced diet containing only fresh cassava products can lead to poisoning, deficiency and deformity. These occur especially if cassava roots have not been sufficiently detoxified and if there is a protein deficiency in particular of amino acids containing sulphur. The latter promote a very effective natural body detoxification process (HAHN, 1989).

The concentrations of hydrogen cyanide in the cassava roots depend on the variety. The content can amount to only a few milligrams but also to over 300 mg per kilogram of fresh root (HAHN, 1989). HCN is also unevenly distributed within the root. There are high concentrations in the outer cell layers and in the upper part of the root (HAHN, 1989). The bitter flavour cassava roots have does not indicate the content of HCN (LANCASTER and COURSEY, 1984).

Hydrogen cyanide does not occur freely in the cassava root but is combined with linamarin and lotaustralin, two cyanoglycosides. HCN is released by means of a hydrolytic process which is activated by the enzyme linamarase (COURSEY, 1982). Hydrolysis always takes place when the enzyme comes into contact with the cyanoglycoside. The natural release of hydrogen cyanide is encouraged by the mechanical destruction of the tissue or the disintegration of the cellular structures due to storage (LANCASTER and COURSEY, 1984).

Drying, boiling, immersing in water over a longer period and fermenting also encourage the release of HCN. What is promoted here is less hydrolysis and more the release of HCN which has already been detached due to the activity of the enzymes with the glycoside.

Even when the cassava roots are properly processed a residue of hydrogen cyanide remains. The concentrations however are mostly so minute that no hazard to health will occur from eating them (HAHN, 1989).