Cyanogenic glucosides in cassava and their toxicity

All cassava plants are cyanogenic in nature, but a wide variation exists in root cyanide levels. Apart from varietal variations, the content is influenced by the age of plant, and cultural and environmental conditions. The level of cyanoglucosides varies widely in different tissues. Accumulation of linamarin in edible roots is influenced by the rate of synthesis in leaf/root, transport from leaves to roots and its turn over in the plant. Control of linamarin levels in roots is most essential in view of its toxic effects. Possible methods include breeding for low-cyanide cultivars, manipulation of cultural conditions and an understanding of the mechanism of accumulation of linamarin in roots so as to devise methods for its control. The simplest way of minimizing toxicity is by processing the roots properly before consumption. A number or processing techniques were adopted in India. Studies indicate that residual levels of cyanoglucosides and their degradation products (acetone cyanohydrin and cyanide) in processed cassava depend on the original levels of cyanoglucosides in fresh roots and on the nature and duration of the processing method. Up to 80 percent cyanoglucoside is removed by boiling and sundrying, while only 20 percent is eliminated by frying, baking, and steaming. Reduction in total cyanogenes is effected by enzymatic decomposition of cyanoglucosides and/or leaching of cyanogenes in water in which roots are boiled, with liberation of volatile HCN. The process of crushing and pounding fresh roots followed by sundrying eliminated as much as 95 percent cyanogens. The extent of toxicity which might result from cassava consumption is determined by relative amounts of free cyanide, acetonecyanohydrin and linamarin in processed cassava. The necessity for developing internationally acceptable standards for permissible levels of cyanogens in cassava food products is emphasized