Cassava root

Gomez, G., M. Valdivieso, J. Santos, and C. Hoyos. 1983. Evaluation of cassava root meal prepared from low- or high-cyanide containing cultivars in pig and broiler diets. Nutr. Rep. Inter. 28 693-704. 

You may be exposed to cyanide by breathing air and drinking water, touching soil or water containing cyanide, or eating foods that contain cyanide. Many plant materials, such as cassava roots, lima beans, and almonds, naturally contain low-to-moderate levels of cyanide. The concentration of hydrogen cyanide in unpolluted air is less than 0.0002 parts per million (ppm ... 

Oral exposure to cyanide usually results from accidental, homicidal, or suicidal ingestion of cyanide salts. Sodium cyanide and potassium cyanide are the most frequently studied cyanide compounds. Copper cyanide, potassium silver cyanide, silver cyanide, and calcium cyanide are other compounds that humans could encounter through oral or dermal exposure. Cassava roots and certain fruit pits contain compounds that can be broken down to form cyanide. Cassava roots form the staple diet of some populations in Africa, Central and South America, and Asia. However, it must be noted that cassava roots are notoriously deficient in protein and other nutrients and contain many other compounds, in addition to cyanide, that could be responsible for some of the observed toxic effects. Thiocyanate is a metabolite of cyanide that is formed in the body after exposure to cyanide compounds. When possible, all oral exposures are expressed as mg CN/kg/day. 

Chronic-Duration Exposure and Cancer. Some reports of occupationally exposed workers indicated that low concentrations of hydrogen cyanide may have caused neurological, respiratory, and cardiovascular effects (Blanc et al. 1985 Chandra et al. 1980, 1988 El Ghawabi et al. 1975 Kumar et al. 1992). The route of exposure was predominantly inhalation, although dermal exposure can also occur in the work place. The studies, however, lacked either information about exposure levels or used small cohorts of workers. Studies in populations that used cassava roots as a main source of their diet described the neurological effects of cyanide consumption (Osuntokun 1972, 1980). However, these effects may be due to a recently identified substance, scopeletin, rather than due to cyanide (Obidoa and Obasi 1991). 

Reproductive Toxicity. No data were located regarding reproductive effects of cyanide in humans. One animal study reported increased resorptions in rats following oral exposure to a cassava diet (Singh 1981). Because some human populations use cassava roots as the main source of their diet, further... 

According to recent reviews, low-cyanide cassava root meal can be included in balanced poultry diets at levels up to 250 g/kg (Garcia and Dale, 1999) or... 

Garcia, M. and Dale, N. (1999) Cassava root meal for poultry. Journal of Applied Poultry Research 8, 132-137. 

Panigrahi, S. (1996) A review of the potential for using cassava root meal in poultry diets. In Kurup, G.T., Palaniswami, M.S., Potty, V.P., Padmaja, G., Kabeerathumma, S. and Pillai, S.V. (eds) Tropical Tuber Crops Problems, Prospects and Future Strategies. Science Publishers, Lebanon, Indiana, pp. 416-428. 

Typical mature roots have different shapes (conical, conical-cylindrical, cylindrical, fusiform) and different sizes (3 to 15 centimeters in diameter), depending on variety, age and growth conditions. The color of the outer peel varies from white to dark brown. The cross-section of cassava roots shows the two major components which are the peel and the central pith (Figure 12.1). The peel is composed of the outer layer (called the periderm) and the inner layer (called the cortical region or cortex), which contains sclerenchyma, cortical parenchyma and phloem tissue. The large central pith of the roots is the starch-reserve flesh, comprised of cambium and parenchyma tissue and xylem vessels. 

Figure 12.1 (a) Cassava roots with conical, conical-cylindrical, cylindrical and fusiform shapes (b) cross-... 

Table 12.2 Contents of total cyanogenic compounds in parenchyma tissue and peel of fresh cassava roots (harvested at 11 months after planting at the early and late rainy periods)...

Starch recovery, as presently practiced, depends on a continuous supply of fresh root. Hence, factories are located close to the root producing areas. In Brazil, the processing season can be as short as six months. In Thailand, continuous processing is possible, although some starch producers are known not to operate during part of the rainy season when the starch content of cassava root is low and operating economics are less favorable. 

Siritunga, D., Arias-Garzon, D., White, W. and Sayre R.T. (2004) Over-expression of hydroxynitrile lyase in transgenic cassava roots accelerates cyanogenesis and food detoxification. Plant Biotechnol. /., 2, 37-43. 

Both linamarin and amygdalin are toxic compounds because they are metabolized to cyanohydrins, which are hydrolyzed to carbonyl compounds and toxic HCN gas. This second step is merely the reconversion of a cyanohydrin to a carbonyl compound, a process that occurs with base in reactions run in the laboratoiy (Section 21.9A). If cassava root is processed with care, linamarin is enzymatically metabolized by this reaction sequence and the toxic HCN is released before the root is ingested, making it safe to eat. 

Naturally occurring cyanohydrin derivatives—linamarin, from cassava root and amygdahn, commonly called laetrile, from apricot, peach and wild cherry pits (Section 21.9B)... 

Starches are the major carbohydrates of such foods as com, wheat, and rice (Table 2,5). Potatoes and legumes are also rich in starches. Most starches are a mixture of amylose and amylopectin, as shown in Table 2.6. in general, amylose constitutes about one-third of the starch in various foods the remainder is amy-lopectin. Of the dry matter of the plants listed in Table 2.4, 70-90% consists of stanch. These plants are called starchy foods. Take special note of the general constituents of the cassava root- (Tapioca is made from cassava.) This food has the loVilest protein/carbohydrate ratio of any of the foods listed in Table 2.5, about 1/25 for cassava compared with about 1/5 for wheat. 

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