Cyanogenic potential of cassava flour: field trial in Mozambique of a simple kit.

The cyanogenic potential (ppm HCN equivalents) of 80 samples of cassava flour (obtained from the Mujocojo and Terrene-A areas of Nampula Province and the markets of Nampula City in Mozambique) were determined using a new simple kit, based on the use of picric acid paper (Egan et al., 1997). The kit is compact, requires only a small amount of water and is very simple to use in the field. Comparison with the results of a semi-quantitative method shows a mean deviation between the two methods of 20% (SD 12%). All samples fitted a single population distribution with a mean value of 45 ppm HCN equivalents (SD 37). Two maxima were observed in the distribution curve at 11-20 and 41-50 ppm. Five samples exceeded 100 ppm with two values of 200 ppm. The WHO safe level for cyanogens in cassava flour is 10 ppm. The lowest levels (2 and 6 ppm) were obtained from cassava flour prepared from sweet cassava. Over 76 samples the mean value of the cyanogenic potential of cassava flour produced by heap fermentation is only one half as large as that produced by sun-drying (P < 0.005). Interventions needed to reduce cyanogen levels are (1) improvements in processing methods, such as replacement of sun-drying by heap fermentation, (2) introduction of additional vegetables, pulses and fruit to alleviate the monotonous cassava diet of the people and (3) introduction of high-yielding, disease-resistant, low-cyanide cultivars.