Assessment of processing methods, sensory attributes, nutritional quality and safety of cassava leaves product (Isombe) in Rwanda

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Sokoine University of Agriculture


Cassava (Manihot esculenta Cranz) leaves are cherished as a vegetable in Africa, but contain a toxic compound, cyanide. Studies were conducted to assess utilization, cyanide and nutritional value of cassava leaves after different preparation procedures in Rwanda. After a survey, leaves from bitter, sweet and wild cassava were: (1) pounded and cooked, (2) dried, pounded and cooked, and (3) pounded, dried and cooked. Drying was done to brittleness in a solar dryer after leaves were blanched. Sensory evaluation was done using a five point hedonic scale, where 5= like very much, 4= like moderately, 3= neither like nor dislike, 2= dislike moderately and 1= dislike very much. Cyanogens, vitamin C, P- carotene, crude protein, iron, calcium, phosphorus, potassium, zinc and moisture content (dry weight basis) were determined in: (i) un-dried, (ii) dried, (iii) un-dried and cooked, and (iv) dried and cooked. Tire chemicals of dry stored samples were also monitored after three, six, nine and twelve months. Results showed that cassava leaves from the three species were consumed as food and sun-drying was a single method used by fanners to extend the storage life. Colour, taste, aroma, texture and overall acceptability were principally affected by processing procedures. Fresh and dry leaves were preferred as vegetable except when they were pounded after drying. After boiling for 30 minutes. cyanide level (40 mg HCN/kg) was above FAO/WHO recommendation (10 mg HCN equivalent/kg) in the relish, but was judged as safe for the fact that it is served in small quantities as side food, reducing the HCN by serving to minor levels in comparison to documented acute oral lethal dose of HCN for an adult (30-210 HCN/60 kg bodyweight). Except vitamin C, amounts of P-carotene, iron, calcium, phosphorus, potassium and zinc were considerable, averaging 340, 153,4264, 3531, 8426 and 54 mg/kg, respectively, and protein (34%) was high and valuable for cyanide human body detoxification. Stored, moisture increased significantly by 6.8% and shelf life was estimated at six months in water, air and light proof material. Further studies in Rwanda on cassava cyanide disorders and approximate safe quantities of cassava leaves relish are recommended.


PhD Thesis


Cassava leaves, Rwanda, Isombe