The chemical composition and cyanide concentration in the foliage of four cassava cultivars (M Col 113, M Col 22, M Col 1684, CM 342-170) were evaluated at four plant ages (6, 8, 10 and 12 months). The effect on cyanide elimination of sun-drying on a concrete floor and of oven-drying at 60°C was also studied, including some observations on the tannin content of dried foliage. The proximal composition, calcium and phosphorus contents, as well as the amino acid composition of dried cassava foliage compared favourably to that of sun-cured lucerne meal. In most cases, foliage from 6-to 12-month-old plants contained 25 to 30% dry matter, and as dried foliage had 13 to 20% crude protein and 16 to 20% crude fibre. Crude protein and crude fibre were the two chemical constituents which varied the most with plant age. The average gross energy of dried cassava foliage was 4.12 kcal kg-' with a range of 3.90 to 4.35 kcal kg-'. Sun-drying eliminated more cyanide than oven-drying (82 to 94% vs 68 to 7696, respectively) and in addition, most of the cyanide in sun-dried foliage was free cyanide (62 to 77%) whereas only 24 to 36% was found as such in oven-dried foliage. Sun-dried foliage samples had consistently lower tannin content than the corresponding oven-dried samples.

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The effect of sun drying on trays for 48 hr and of oven drying in an air-forced oven at 60°C for 24 hr on the cyanide content of chips of ten cassava varieties was studied. Fresh cassava chips from whole roots of these varieties showed significantly different total cyanide contents among them with values in the range of 100-900 mg/kg on a dry matter basis; most of the varieties studied exhibited cyanide contents in the range of 200-600 mg/kg. The free cyanide proportion in the fresh chips was in the range of 30-40% of their total cyanide. Sun and oven drying reduced the cyanide content in the dried chips to approximately 15-30% of the initial cyanide content of fresh chips. In addition, the free cyanide content in dried chips accounted for approximately 60-80% of their total cyanide value.

The effects of three oven drying temperatures (60,70 and SOT), each at three loading rates (10. IS and 20 kg/m') on cyanide elimination from cassava whole-root chips were evaluated. Roots of two cassava cultivars, one with high (M Col 1684) and the other with intermediate (M Col 22) cyanide contents, were used. A total of twenty-seven drying experiments with chips of cv. M Col 1684 and eighteen with M Col 22 were evaluated in two factorial experiments 3 x3 x3, (temperaturex loadingx replicate) and 3 X 3 X 2, respectively. The main factor determining cyanide elimination was the loading rate rather than the drying temperature under these conditions. As the loading increased from 10 to 20 kg/m2 the total and bound cyanide contents of dried chips decreased as a result of the higher cyanide losses. 'IThis effect was statistically significant only with the chips of the high-cyanide-containing cultivar but the same trend was observed with M Col 22. Artificial drying at the temperatures and loadings assayed allowed total cyanide losses of 81 and 69% for chips of cv. M (20122 and M Col 1684, respectively; the residual cyanide content of dried chips of cv. M Col 1684 was three times the maximum permissible level set by the EEC for hydrocyanic acid in cassava products to be used as animal feeds. These experimental results are compared with previously published data on cyanide elimination.

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