Quantification of Different Cyanogenic Compounds in Processed Cassava roots and in water used for soaking

Abstract

Roots of Cassava (Manihot esculenta Crantz) are known to contain cyanogenic compounds that are hazardous to health if consumed without adequate processing. There are several traditional processing methods that are often applied with the view of reducing cyanogenic compounds in cassava roots. Sundrying and soaking of cassava roots are the most commonly used traditional methods in Tanzania. The present study was undertaken to quantify total cyanogen, glucosides, cyanohydrin and free cyanide (HCN) present in both processed cassava products and waste water used for soaking. Samples of fresh cassava roots were obtained from Mikese village in Morogoro region in Tanzania. Traditional processing methods of sundrying and soaking were simulated in the laboratory. Cyanogenic residues during processes of sundrying and soaking, in flour, and in “Ugali” were determined by using a modification of the enzymic calorimetric method of Cooke (1978). The processing stages in both soaking and sundrying were observed to be effective in cyanogen removal. Soaking method alone reduced total cyanogen from 298.1 ± 23.2 mg/kg d.w.b. to 50.1 ± 6.8 mg/kg d.w.b. in the sixth day of soaking. Sundrying method reduced cyanogen from 302.4 ± 26.3 mg/kg d.w.b. to 146.5 ± 16.3 mg/kg d.w.b. in the fifth day of sundrying. “Ugali,” a traditional meal prepared from flour obtained from soaked cassava roots was found to contain total cyanogen of 18.2 ± 3.12 mg/kg d.w.b. whereas that prepared from flour obtained from sundrying of cassava roots had 43.6 ± 6.5 mg/kg d.w.b. of the same type of cyanogen. Based on these results, soaking of cassava roots in water was found to be the most effective method in reducing cyanogenic compounds in cassava roots.Wastewater used for soaking cassava roots contained total cyanogen up to a level of 172.20 ± 8.38 mg/l. This level is by far above WHO (1982) recommended upper limit of 0.2 mg/l. With this level of cyanide, wastewater used for soaking cassava roots, which is often discarded haphazardly, may amount to environmental pollution particularly if large quantities of cassava roots are to be processed through soaking.