Abstract
Cassava leaves are largely consumed as vegetable in African, but contain a toxic compound, cyanide. To ascertain their safety and contribution to human nutrition, after a number of pre-treatments preceding their boiling in water, cyanide, vitamin C, β-carotene, crude protein, iron, calcium, phosphorus, potassium and zinc contents were assessed in leaves from bitter, sweet and wild cassava species, boiled for 15 and 30 min after differently processed by: (1) pounding un-dried (UND), (2) drying before pounding (DBP) and (3) drying after pounding (DAP). Blanching headed drying was done in a tunnel solar dryer. Results showed that cassava species, processing procedures, and boiling time significantly (p < 0.05) reduced cyanide and the nutrients. However, except vitamin C, eliminated to almost nil, other nutrients were retained at considerable levels. Sensibly decreased by drying and/or boiling, cyanide levels ranged from 32 - 50 mg HCN/kg (dry matter basis) after boiling for 30 min. These levels, above the recommended level (10 mg HCN/kg) for foods, were safe with regard to cyanide toxicity based on the fact that the vegetable is served in small quantities as side food. consumed quantities of relishes as side foods. Nevertheless, it was advisable not to make them the everyday foods, especially to lower body weight such as children, and to extend time of cooking. Key words: Cassava leaves, cassava species, processing procedures, cyanide and nutrients, Rwanda.
Highlights
Cassava is a very important crop in the tropics and a staple food for over 800 million people (Nassar et al, 2007), growing over a range of climates and altitudes and on a wide variety of soils (FAO/IFAD, 2005)
Pressure, and use of enzyme, or mineral acids, cyanogenic glucosides are decomposed into acetone cyanohydrins which, at pH above 5 or temperatures above 35°C, is broken down, spontaneously, into poisonous compound, hydrogen cyanide (HCN) (Siritunga and Sayre, 2004)
In order to minimize the effects of age, environment and soil type on chemical composition, leaves samples of the same age were selected from the same field, Rwanda Agricultural Board (RAB)’s field at the Karama Research Station, in Bugesera District of Eastern Province of Rwanda
Summary
Cassava is a very important crop in the tropics and a staple food for over 800 million people (Nassar et al, 2007), growing over a range of climates and altitudes and on a wide variety of soils (FAO/IFAD, 2005). Cassava and cassava leaves contain cyanide, in the form of cyanogenic glucosides, primarily linamarin and small lotaustralin (Uyoh et al, 2007). The cyanogenic glucosides are distributed throughout the cassava plant, with highest levels in leaves (Etonihu et al, 2011). Pressure, and use of enzyme (linamarase), or mineral acids, cyanogenic glucosides are decomposed into acetone cyanohydrins which, at pH above 5 or temperatures above 35°C, is broken down, spontaneously, into poisonous compound, hydrogen cyanide (HCN) (Siritunga and Sayre, 2004). Cyanohydrins are the most dangerous form of the cyanide because at the elevated pHs and temperatures present in the human body, it rapidly decomposes to release the poisonous hydrogen cyanide. The synthesis of thiocyanate requires sulphur-containing amino acids, as a consequence of protein intake (CCDN, 2007)
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