CASSAVA(FOOD OF PLANT ORIGIN) TOXICOLOGY

Cassava contains the cyanogenic glucoside, linamarin and lotaustralin; linamarin being present in quantity up to 90% of the total.

These are hydrolyzed by the enzyme, linamarase to yield free hydrogen cyanide. In the intact cassava tissue, linamarin is separated from the enzyme linamarase.

Cyanide is exceedinly toxic to man and domestic animals if consumed in amounts in excess of 25-30ppm.

Cassava tubers must therefore be detoxified and the liberated cyanide subsequently eliminated before consumption.

The elimination of cyanide in different cassava-based foods is based on the fact that free cyanide is both water soluble and heat volatilizable while bound cyanide can be converted by enzyme or heat hydrolysis to give water soluble, heat volatilizable hydrogen cyanide.

The detoxification mechanism involes: (1) The conversion of bound cyanide to free cyanide by enzyme and heat hydrolysis.
(2). The removal of free cyanide by repeated leaching with water and by heat volatilization.

The various process steps associated with the detoxification of different cassava-based products include:
1. Grating which exposes the glucoside to linamarase for hydrolysis to prusic acid.

2. Fermentation, during which linamarin and lotaustralin are broken down into harmless components.

3. De-watering, which eliminates a substantial quantity of hydrogen cyanide.

4. Cooking and heat toasting, which can also destroys hydrogen cyanide.

Residual cyanide in most cassava products can be neutralized by the enzyme, rhodanase- an organic catalyst found in human cells.

Vitamin B12 from food of animal origin can also neutralize residual cyanide.

With cystine obtained in the diet, the human body is also capable of counteracting hydrogen cyanide.

The consumption of cassava products with high levels of cyanide over a long period has been linked to ailments such as "tropical ataxic neuropathy" and "goitre".


REFERENCES

Adeyemi, I. A. and Balogh, E. (1985). Biotechnology in Food Processing: Prospects in Nigeria. Nigeria Food Journals vol 2, nos 2&3.

Brownsell, V. I., Griffith, C. J. and Eleri, J. (1992). Applied Science Food Studies. Longman Scientific & Technical; UK