Processing of cassava roots to remove cyanogens

Abstract

A simple equation is developed between the total cyanide contents of cassava root parenchyma and the processed product with the % retention of cyanide on processing. This equation is applied to different methods of processing used worldwide. Thus to produce cassava flour of 10 mg HCN equivalents/kg flour (ppm), the WHO safe level, by sun drying or heap fermentation requires starting with sweet cassava containing 12–32 ppm total cyanide. In an average year only 14% of flour samples in our study areas in Nampula Province of Mozambique had total cyanide contents of <10 ppm. Distribution curves of flour total cyanide show that the percentage of samples exceeding 100 ppm total cyanide increased from 6% in an average year to 43–65% in a low rainfall year, when cases of konzo also occurred. Processing methods used to produce farinha in Brazil and gari in West Africa reduce the total cyanide content to less than one eighth of that using heap fermentation and less than one sixteenth of that using sun drying. Heap fermentation and sun drying, commonly used in eastern and southern Africa, do not adequately remove cyanide in a normal year and are hopelessly inadequate when used on cassava grown during drought. New and greatly improved processing methods are urgently needed. The high levels of cyanide intake in central, eastern and southern Africa from high cyanide flour are the most likely cause of konzo in young people and the very long term consumption of gari of lower cyanide content in West Africa is the most likely cause of TAN in older people.