Cassava, hydrocyanic acid

Casadei, E., P. Jansen, A. Rodrigues, A. Molin, and H. Rosling. 1984. Mantakassa an epidemic of spastic paraparesis associated with chronic cyanide intoxication in a cassava staple area of Mozambique. 2. Nutritional factors and hydrocyanic acid content of cassava products. Bull. World Health Org. 62 485-492. 

Tapioca%—The tubers, about 30 pounds in weight, of Manihot utilissima or Cassava in Brazil are washed, peeled, and pounded to pulp and pressed in baskets to wash out the starch. This is then heated on iron plates at a gentle heat to volatilize the hydrocyanic acid. The grains swell, burst, and-agglutinate. 

Nutritional factors and hydrocyanic acid content in cassava. Bull WHO 62 485-492. 

Cassava (tapioca or manioc) is the principal food of many people living in the tropics. The juice must be washed from the grated root before it is eaten, because many varities contain hydrocyanic acid. After drying, cassava still contains rather less than 2% of protein and understandably protein-energy malnutrition is common in all communities that depend on it for most of their food. 

The different varieties contain variable amounts of linamarin, a substance that may be converted into toxic prussic (hydrocyanic) acid by an enzyme present in the plant tissues. The tubers which contain moderate to large amounts of linamarin usually have a bitter taste, whereas those that are low in the toxicant are likely to be slightly sweet. Also, the outer layer (rind) of a tuber of the bitter variety has a notably higher level of linamarin than the inner layers. Nevertheless, all varieties of cassava should be processed to minimize the likelihood of toxicity, which varies according to the local soil and climatic conditions. 

CAUTION Cassava must be washed thoroughly (or boiled, dried, expressed, or fermented) to remove the prussic (hydrocyanic) acid. Because of this acid, the bitter cassava root cannot be eaten raw. Also, a cassava-rich diet should be supplemented with animal protein foods (rich in vitamin B-12) to assure that any residual traces of prussic acid are handled safely by the body. 

Cassava is a tropical root crop used as a staple food in many parts of Africa and South America. It contains the glucoside of acetone cyanohydrin, linamarin (I), which is broken down by an endogenous enzyme, linamarase, with the formation of hydrocyanic acid ... 

The enzyme is not released until the root tissue is bruised, so cassava is traditionally peeled, sliced and cooked by boiling in the open. The hydrocyanic acid, boiling at 26 °C, is released and dispersed harmlessly to atmosphere, and the cooked cassava is safe to eat. 

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