Variation of Cyanide Levels in Processed Sweet Cassava (Manihot Esculenta Crantz) Leaves Grown in Busia and Kilifi Counties, Kenya
Ojiambo, Ogombe Charles
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Cassava (Manihot esculenta Crantz) is the third most important food source around the world especially in sub - Sahara Africa. It is preferred due to its agronomical attribute such as ability to grow in poor soils and drought resistance. The consumption of its tubers and leaves has dual antagonistic contribution to mankind. On one hand, this perennial tropical crop contains carbohydrates, vitamins, calcium and iron which are of nutritional benefit while on the other hand, they contain cyanogenic glycosides. The latter when hydrolyzed by the enzyme linamarase produces hydrogen cyanide which is poisonous and can lead to upper motor neuron spatic paraparesis (Konzo condition). A number of deaths have been reported associated with consumption of cassava containing more than WHO allowed levels of 10 mg HCN equivalent/Kg body weight. This has been mainly attributed to among other factors, the methods of processing tubers and leaves. Proper processing is therefore necessary before consumption and it is therefore in this light that this study monitored the variation of cyanide levels following different processing methods of leaves of sweet cassava varieties. Leaves of sifurosa, adhiambolera, nambamunane, maachure and palisa varieties and kabandameno, munguvu mambasa and mzazakahu varieties were purposively sampled from Busia and Kilifi Counties in Kenya respectively. Prior to boiling the leaves for up to 25 minutes, two processings’ were done; one involved leaves being pounded to form a soft paste while in the other, leaves were pounded followed by soaking in water. Unpounded leaves were also boiled for the same duration. Determination of cyanide levels was done using picrate papers and UV - Vis spectrophotometer and data analyzed by Student t - test and Analysis of Variance. The cyanide levels ranged from (576.30 0.32 - 128.34 0.34) mg HCN equivalent/Kg in raw cassava leaves. There were significant differences (P < 0.001) in levels of cyanide in varieties grown under the same environmental conditions and in different environmental conditions. The initial cyanide levels significantly reduced by 85.17%, 90.88% and 91.00% after 25 minutes of boiling unpounded, pounded and pounded then soaked leaves respectively (P < 0.001). However, unpounded leaves still retained cyanide levels above the WHO recommended levels after boiling for 25 minutes. The findings of this study promote longer duration of boiling cassava leaves with prior processings’ of pounding and that of pounding and soaking to minimize the risks associated with cyanide poisoning. A sensitization campaign is recommended following these findings in order for consumers of cassava leaves to be well informed on the processing procedures that reduce the toxic cyanide levels. It further necessitate adoption of internationally acceptable standards for permissible levels of HCN in cassava food products.