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.

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SummaryUltrasonic disruption of powdered Merino wool in formic acid and dichloroacetic acid causes some protein to be dissolved, but the amino acid content of the residual wool is unchanged by the treatment. Cortical cells and disrupted cortical cells are found to have the same composition as the parent fibre, which is to be expected because the latter consists of about 90 % cortical cells. However, the cuticle of Merino wool is different in composition from the parent fibre, being richer in cysteic acid, serine, proline, glycine, valine, and cystine, and poorer in aspartic acid, threonine, glutamic acid, methionine, isoleucine, leucine, tyrosine, phenylalanine, and arginine than the whole fibre. Thus the cuticle is considerably less polar than the fibre as a whole. With the exceptions detailed below, it is found that the first group of amino acids listed above are classified as non a.helix.forming and the second group as a·helix· forming by Blout (1962). The exceptions are isoleucine and threonine, whilst arginine and glycine are not classified. It is therefore postulated that the cuticle is amorphous because of its high content of non a·helix.forming amino acids. The cuticle of Lincoln wool shows similar differences to those already given for Merino cuticle but, in addition, contains less lysine and histidine than the whole fibre.

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