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Cassava leaves are a valuable source of protein but the cyanogenic potential limits their use as food and feed. Four different treatments were investigated to detoxify cassava leaves. Thermal (55 °C for 6 hr), sodium bicarbonate (0.4% NaHCO 3 , 55 °C for 6 hr), enzymatic (0.32% Multifect® GC Extra, 4 hr), and ultrasonic treatments (500 W, 35 kHz, 55 °C, 0.25 hr) reduced the total cyanide (µg HCN equivalents per g fresh leaf or ppm) content by 90%, 93%, 82%, and 84% while the cyanide content reduction in the respective controls was 85%, 90%, 79%, and 84%, respectively. The sodium bicarbonate treatment was found to be the most effective treatment. Therefore, it was further optimized by varying time and temperature. A significant effect on the cyanide content was observed by changing the incubation time while no significant effect of temperature was noticed. Nevertheless, extended incubation time during sodium bicarbonate treatment reduced ascorbic acid content by 7% and 39% when leaves were incubated with sodium bicarbonate for 0.5 hr and 48 hr, respectively. PRACTICAL APPLICATION: Cyanogenic glucosides are the major toxic compound in cassava leaves, which limits their use as food and feed. The methods proposed in this study can be used to detoxify cassava leaves, which are generally considered as an inferior by-product. Hence, detoxified cassava leaves may contribute to fulfil world protein demand in an eco-sustainable way., (© 2019 Institute of Food Technologists®.)

Toxicity of cassava arises due to the presence of the cyanoglucosides linamarin and lotaustralin which are hydrolysed by endogenous enzyme linamarase to acetonecyanohydrin (ACN) and cyanide (CN) which are toxic. Major research efforts to eliminate/reduce cyanoglucosides have focused on (i) development of acyanogenic cassava varieties by breeding; (ii) controlling its metabolism; and (iii) processing to remove cyanogens. The cyanoglucoside (CNG) content in cassava is genetically controlled and cultivars may be classified as low (<50 μg/g), medium (50-100 μg/g) and high CN (>100 μg CN eq./g) varieties. Molecular techniques for reducing tuber CNG have focused on development of transgenic plants with reduced expression of cyt P 450 in leaves, or increased expression of hydroxynitrilelyase in tuber. For immediate solution, CNG content can be reduced using several processing methods. Traditional methods used for processing include boiling, drying, parboiling and drying, baking, steaming, frying and preparation of flour. These processes result in CN losses ranging from 25% to 98%. The cyanogen level in the final product is influenced both by the tuber CNG and the method of processing. In order to achieve safe levels of 10 μg/g in cassava products, new methods of processing, especially for cassava containing more than 250 μg CN eq./g, remains a challenging problem., (Copyright © 2010. Published by Elsevier Ltd.)

Exposure to cyanide from gari, a popular cassava food in West Africa, is implicated in the causation of ataxic polyneuropathy and amblyopia, but this has been questioned because cyanide was not detected in gari in a study. This study was carried out to determine if gari is a source of exposure to cyanide. Gari (150 g) containing cyanohydrin, from which 128 micromol of cyanide ions could be released, was dissolved in 500 ml of cold water for each of the 12 healthy subjects to drink. Concentrations of cyanide in plasma and erythrocytes were determined at baseline and following the meal at 30 min, 1 h, hourly for 4 h and two hourly for 12 h. The mean concentrations of cyanide in the plasma were 6 micromol/l (95% CI 2-10) at baseline, 12 micromol/l (95% CI 6-17) at peak and 6 micromol/l (95% CI 2-10) on return to baseline. The mean amount of cyanide absorbed into the plasma was 13 micromol (S.D. 12), while the transit time of absorbed cyanide was 7.3 h (S.D. 2.1). This study shows that exposure to cyanide follows consumption of gari, but the amount of cyanide absorbed into the plasma from a single meal is small and unlikely to cause acute intoxication. The long transit time of absorbed cyanide in the plasma suggests that frequent intake of gari could cause cyanide to accumulate in the plasma.

Neurological disorders have been reported from parts of Africa with protein-deficient populations and attributed to cyanide (CN-) exposure from prolonged dietary use of cassava, a cyanophoric plant. Cyanide is normally metabolized to thiocyanate (SCN-) by the sulfur-dependent enzyme rhodanese. However, in protein-deficient subjects where sulfur amino acids (SAA) are low, CN may conceivably be converted to cyanate (OCN-), which is known to cause neurodegenerative disease in humans and animals. This study investigates the fate of potassium cyanide administered orally to rats maintained for up to 4 weeks on either a balanced diet (BD) or a diet lacking the SAAs, L-cystine and L-methionine. In both groups, there was a time-dependent increase in plasma cyanate, with exponential OCN- increases in SAA-deficient rats. A strongly positive linear relationship between blood CN- and plasma OCN- concentrations was observed in these animals. These data are consistent with the hypothesis that cyanate is an important mediator of chronic cyanide neurotoxicity during protein-calorie deficiency. The potential role of thiocyanate in cassava-associated konzo is discussed in relationship to the etiology of the comparable pattern of motor-system disease (spastic paraparesis) seen in lathyrism.

1. The effects of drying cassava root at different rates on its composition and toxicity to broiler chicks were examined. Unpeeled roots from a high-cyanide cultivar of cassava were chipped and dried at 25 degrees C to a moisture content of below 100 g/kg over 24 h for fast-dried meal (FD) or 72 h for slow-dried meal (SD). The meals were incorporated at 250 and 500 g/kg into semi-synthetic diets which were fed to day-old broiler chicks as mash or pellets in separate experiments. 2. The two drying rates produced meals with similar concentrations of polyphenols, but different concentrations of cyanogens, the latter being 38 and 482 mg total cyanide/kg for SD and FD, respectively. The linamarin, acetonecyanohydrin or total cyanide content measurements of pelleted diets were highly correlated. 3. Growth rates of chicks fed on SD-based diets were significantly higher than those of chicks fed on FD-based diets. Compared with a control diet, weight gain of chicks fed on the 500 g FD/kg diet (containing 258 mg total cyanide/kg) was 77% lower, although performance also appeared to be reduced at 142 mg total cyanide/kg. 4. The ratio of water:food intake of chicks was higher in FD than in SD groups, and this was reflected in the high water content of excreta. There was increased bile excretion, the chloretic effect increasing with the cyanogen content of diet. Pancreas weights were lower in FD than in SD groups in experiment 1 (mash diets), but not in experiment 2 (pelleted diets), while there was a significant interaction between drying method and cassava inclusion rate on liver weight in experiment 2, but not in experiment 1. There were no effects on the mortality rate. 5. Pelleting of diets generated high temperatures, but did not significantly alter the cyanogen concentration or the growth of the chicks. 6. Thus, slower rates of drying cassava roots produce meals with lower cyanogen concentration that are, consequently, less toxic to broiler chicks. Cassava root meal of less than 40 mg total cyanide/kg can be fed to broiler chicks at 500 g/kg without any adverse effects.

Effects of cassava (Manihot esculenta Crantz)-borne organic cyanide and inorganic cyanide in the form of sodium cyanide on bone and muscle development were investigated in eighteen dogs of Nigerian breed. After 16 weeks of stabilization in the laboratory from the time of purchase when the dogs were fed on the same diet, they were randomly assigned to three experimental groups of six dogs each. The control group was fed on rice while the other two groups were fed on either cassava (gari) or rice plus cyanide. The three diets were made isoenergetic and isonitrogenous by varying the quantity of meat incorporated into them. The results obtained after 14 weeks of feeding the respective diets indicated that there was retardation of muscle development in the gari-fed dogs. This may have resulted from gluconeogenesis from muscle protein associated with suppression of production of insulin by the pancreas in this group. The results indicated also that the effects of inorganic dietary cyanides on muscle development were different. Both forms of dietary cyanides, however, had no adverse effect on bone development.