Farmers' perceptions on the causes of cassava root bitterness: A case of konzo-affected Mtwara region, Tanzania

Impact of Seasonal Variation and Processing Methods on the Cassava-Derived Dietary Cyanide Poisoning, Nutritional Status, and Konzo Appearance in South-Kivu, Eastern D.R. Congo

This study aimed at evaluating the impact of seasons on the nutritional status and on dietary cassava-related cyanide exposure in Burhinyi and Idjwi, two areas in the eastern Democratic Republic of the Congo, witnessing similarly high cassava-derived cyanide poisoning but differently affected by konzo and malnutrition. Cyanide content in cassava roots and flour, and urinary thiocyanate levels (uSCN) of 54 subjects (40 from Burhinyi and 14 from Idjwi, aged 28.7 (12.1) years, 63% women) were measured during the rainy season (RS) and dry season (DS), using picrate paper kits A and D1. Local processing methods proved to be efficient in removing cyanogenic compounds in fresh cassava roots during the RS. However, the cyanide content in flour samples significantly increased during DS, with ~50% of samples containing unsafe levels (>10 ppm) of cyanide content. Strikingly, the uSCN (µmol/L), from being comparably high in RS (~172.0), slightly decreased during DS in Burhinyi (~103.2; p = 0,3547), but not in Idjwi (~172; p = 0,1113). Furthermore, serum proteins and albumin levels significantly decreased during the DS, witnessing a worsening of nutritional status, in Burhinyi but not in Idjwi. The consumption of bitter cassava roots (OR = 5.43, p = 0.0144) and skipping heap fermentation (OR = 16.67, p = 0.0021) were independently associated with very high uSCN levels during the DS. Thus, restoring the traditional processing methods, and complying with them in either season should ensure the safe consumption of cassava.

Cassava Orange-Fleshed Sweetpotato Composite Gari: A Potential Source of Dietary Vitamin A

Gari, a fermented granular cassava food product, continues to play a major role in the diets of West Africans. The white cassava commonly used for this product is devoid of provitamin A but may have a significant concentration of cyanogenic compounds. The physicochemical and functional properties of partial substitution of cassava with orange-fleshed sweetpotato (OFSP) to process gari were investigated. Two commonly consumed products "eba" and "soaked gari" were prepared from the various formulations and sensorially assessed. Cassava OFSP composite gari (77% cassava:23% OFSP, 75% cassava:25% OFSP, and 73% cassava:27% OFSP) did not significantly (p > 0.05) influence the moisture content (3.39%-5.42%, p = 0.38), water absorption capacity (589-671 mL/g, p = 0.22), and swelling index (3.75-4.17, p = 0.08) compared with that of 100% cassava gari. Expectedly, increasing the levels of OFSP incorporation significantly (p < 0.001) resulted in color change from white (L* = 83.99, a* = 0.93, b* = 16.35) to orange (L* = 69.26, a* = 7.74, b* = 28.62). For β-carotene, the 73% cassava:27% sample was ~5.2 times more than the level in 100% cassava gari. Also, it had lower residual cyanogenic compounds (0.37 vs. 1.71 mg/kg, p < 0.001, measured as hydrogen cyanide) compared with cassava-only gari. The sensory scores by the 100 panelists using a five-point hedonic scale (1 = dislike extremely to 5 = like extremely) exceeded the minimum threshold (3) for acceptance. Within the limits of this study, OFSP can be composited with cassava up to 27% to process gari that has similar physicochemical properties and sensorial preference as that of cassava only. Furthermore, the OFSP-composited gari contains a significant amount of provitamin A and have a reduced residual cyanogenic compound. Thus, the composited gari could play a significant role in addressing vitamin A deficiency in Ghana compared to the 100% cassava only.

Konzo risk factors, determinants and etiopathogenesis: What is new? A systematic review

Konzo is a toxico-nutritional upper motor neuron disease causing a spastic paraparesis in schoolchildren and childbearing women in some African countries. Almost a century since the first description of konzo, its underlying etiopathogenic mechanisms and causative agent remain unknown. This paper aims at refreshing the current knowledge of konzo determinants and pathogenesis in order to enlighten potential new research and management perspectives. Literature research was performed in PubMed and Web of Science databases according to the PRISMA methodology. Available data show that cassava-derived cyanide poisoning and protein malnutrition constitute two well-documented risk factors of konzo. However, observational studies have failed to demonstrate the causal relationship between konzo and cyanide poisoning. Thiocyanate, the current marker of choice of cyanide exposure, may underestimate the actual level of cyanide poisoning in konzo patients as a larger amount of cyanide is detoxified via other unusual pathways in the context of protein malnutrition characterizing these patients. Furthermore, the appearance of konzo may be the consequence of the interplay of several factors including cyanide metabolites, nutritional deficiencies, psycho-emotional and geo-environmental factors, resulting in pathophysiologic phenomena such as excitotoxicity or oxidative stress, responsible for neuronal damage that takes place at sparse cellular and/or subcellular levels.

Soil nutrient adequacy for optimal cassava growth, implications on cyanogenic glucoside production: A case of konzo-affected Mtwara region, Tanzania

Soils in areas affected by konzo (a cassava cyanide intoxication paralytic disorder) are predominantly infertile and probably unable to supply cultivated cassava with the nutrients it needs to achieve optimal growth. Soil nutrient supply in these areas could also be influencing cyanogenic glucoside production in cassava, however there is hardly any knowledge on this. An assessment of soil nutrient levels on crop fields in konzo-affected areas was therefore carried out to determine their adequacy for optimal cassava growth. Konzo-affected Mtwara region of Tanzania, was used as a case study. Whether soil nutrient supply influences cyanogenic glucoside production in cassava cultivated in konzo-affected areas and how it could be doing this, was additionally investigated. To investigate this, correlations between total hydrogen cyanide (HCN) levels (a measure of cyanogenic glucoside content) in cassava roots and various soil nutrient levels on crops fields were carried out. This was followed by an investigation of relationships between cases of cassava cyanide intoxication and soil nutrient levels on crop fields from which the consumed toxic cassava roots had been harvested. Cases of cassava cyanide intoxication were used as a proxy for high cyanogenic glucoside levels in cassava roots. Logistic regression analysis was used in the latter investigation. Other important non-nutrient soil chemical characteristics, like pH and soil organic carbon, were also included in all analysis performed. The results revealed that most soil nutrients known to have reducing effects on cassava cyanogenic glucosides, like potassium (mean = 0.09 cmol/kg, SD = 0.05 cmol/kg), magnesium (mean = 0.26 cmol/kg, SD = 0.14 cmol/kg) and zinc (mean = 1.34 mg/kg, SD = 0.26 mg/kg) were deficient on several crop fields. The results also showed that cyanogenic glucosides in cassava roots could be increased with the increased supply of sulphur in soils in bitter cassava varieties (r_s = 0.593, p = 0.032), and with the increased supply of P in soils in all cassava varieties (r_s = 0.486, p = 0.026). The risk of cassava cyanide intoxication occurring (and thus high cyanogenic glucoside levels in cassava) was found to be likely increased by cultivating cassava on soils with high pH (X² = 8.124, p = 0.004) and high iron (X² = 5.740, p = 0.017). The study managed to establish that cassava grows under conditions of severe nutrient stress and that soil nutrient supply influences cyanogenic glucoside production in cassava cultivated in konzo-affected areas of Mtwara region. Despite the multiple soil nutrient deficiencies on crop fields, low soil fertility was however not the only probable cause of increased cyanogenic glucosides in cassava, as high soil nutrient levels were also found to be potential contributors.