EVALUATION OF THE EFFECT OF VARIOUS PROCESSING TECHNIQUES ON CYANOGEN CONTENT REDUCTION IN CASSAVA

Cassava is an important carbohydrate source for millions of people in the tropics. In India, its roots and leaves are used as human food, animal feed and industrial raw material. Because of the presence of the cyanogenic glucosides, linamarin and lotaustralin, in cassava and their hydrolysis by the endogenous enzyme linamarase to cyanohydrins which break down to hydrogen cyanide (HCN), cassava consumption is often linked with cyanide toxicity. In southern India, a variety of techniques such as boiling, baking, steaming, deep frying and sun-drying both blanched and raw chips are adopted for processing roots for consumption. Residual levels of cyanogenic glucosides and their toxic degradation products, cyanohydrins and free cyanide, in processed cassava depend upon the original levels of cyanogenic glucosides, and on the nature and duration of the method used for processing. Up to 80% of the glucosides is removed by boiling and sun-drying, while only about 20% is eliminated by frying, baking and steaming. Reduction in total cyanogens is effected by enzymatic decomposition of cyanogenic glucosides and/or leaching of cyanogens in the water in which the roots are boiled, with liberation of volatile HCN. The process of crushing and pounding fresh roots followed by sun-drying eliminates as much as 95% of the cyanogens. This is the most effective of the methods used in India for reducing the cyanogen content of cassava roots. Boiling of leaves removes about 85% of the cyanogenic glucosides.

Careful and effective processing can render even high cyanogen cassava safe for consumption. The necessity for developing internationally acceptable standards for permissible levels of cyanogens in cassava food products is emphasized.