Determination of cyanide concentration levels among cassava (Manihot esculenta Crantz) germplasm in Kenya

Abstract

Cassava (Manihot esculenta Crantz) is a major carbohydrate source in the human diet, yet certain varieties harbor high cyanogenic glycoside concentrations, posing risks of cyanide toxicity. This study sought to determine cyanide concentration levels in leaves, peels, and pulps of cassava varieties selected from earlier morphological characterization studies carried out in Kenya. A total of 32 varieties were selected for cyanide content analysis using picrate paper and spectrophotometric methods. Similarly, an on-field study was conducted in Migori County, Kenya to assess cyanide concentrations in cassava varieties grown by farmers using picrate paper method. Using the spectrophotometric method, the leaves, peels and pulps had overall average cyanide concentrations of 5.89 mg/L CN- , 7.42 mg/L CNand 8.20 mg/L CNrespectively. The same trend was realized using the picrate paper analysis where the leaves had average cyanide concentration of 3.13 mg/L CN- , the peels had average 5.44 mg/L CNand the pulp had the highest average cyanide concentration of 7.97 mg/L CN- . Using the spectrophotometer analysis of the leaves, the variety Nyarkadera exhibited the highest cyanide concentration of 26.93 mg/L CN- , while the lowest was observed in the varieties Nyatanga – 002, Nyakanyamkago and Kasukali (0.40 mg/L CN- ). Peels of Kazanzwara recorded the highest cyanide concentration of 17.82 mg/L CN- , whereas Kasukali showed the least cyanide concentration of 1.19 mg/L CN- . Results obtained from the pulps showed that the variety Nyatanga had the highest cyanide concentration of 26.93 mg/L CN- while the least cyanide concentration was recorded on the variety Mzungu (0.40 mg/L CN- ). Based on the two techniques of analyses, the study established moderate positive correlations (r=0.547 and r=0.570) between cyanide levels in leaves and peels of different cassava varieties respectively. A strong positive correlation of r=0.936 was found in the analysis of pulps indicating high consistency of the two methods. In the field study 15 varieties out of 32 had high cyanide concentrations between 10-30 mg/L CN- while 17 varieties had low cyanide concentration. This showed that farmers still planted high and low cyanide varieties in almost equal proportions. The picrate paper analysis was found appropriate for use effectively in assessing cyanide concentrations in the field. The variability in cyanide levels among the cassava accessions appeared to emphasize need to characterize varieties by cyanogenic potential for breeding programs and consumer guidance