Critical stages in cyanogen removal during cassava processing in southern Tanzania

Cassava processing was studied in villages in southern Tanzania. The established method of 17 days sun-drying of longitudinally split roots only reduced cyanogenic glucosides to 27–37%, leaving more than 100 mg HCN equiv per kg dry wt of flour, that is 10 times the safe level set by FAO/WHO. The cyanohydrins yielded remained high during sun-drying but fell to safe levels in dry products. Short-cut processing by alternating pounding and drying to make flour in a day removed glucosides more effectively but cyanohydrin levels ranged between 23 and 124 mg HCN equiv per kg dry wt, in such flour. Ingested cyanohydrins will yield cyanide in the alkalinic environment of the gut and may be much more toxic than equimolar amounts of glucosides, because high levels of glucoside are found to be excreted intact in humans ingesting flour with high glucoside content.