Comparation of the Effect of Microalgae and other Treatments on the Cyanide Content of Fermented Garri.

Comparation of the Effect of Microalgae and other Treatments on the Cyanide Content of Fermented Garri.

Food crops are important sources of food for the human population and are used as food from which energy is derived to drive biochemical processes in the body anabolic and catabolic routes. In Nigeria, cassava (Manihot escunlenta), is an energy food and individuals generates ATP (Adenosine triphosphate) from the glucose content of this food crop (Okafor, 2004).

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However, Cassava has some constituents like cyanide that are toxic to mammals when harmful amount is consumed. Such levels could lead to serious side effects such as headaches, vomiting, chest pain, blood changes, thyroid gland enlargement, effects on the brain and heart, goiter and partial paralysis. These common food crops identified ultimately, are subjected to varying processing treatments before consumption by humans and needs evaluation of the potential processing effects on the cyanide content (Okafor, 2004).It is an important source of calories because it covers 60% of the daily calorific needs of the populations in tropical Africa and in Central America (Nartey, 1998). In central Africa, notably in Congo, cassava roots are mainly consumed in the form of cassava bread, locally named Chikwangue whereas in Nigeria (West Africa), it is consumed either as garri or fufu. Besides, the cassava leaves are good for human consumption because of their high nutritional value. Cassava leaves are rich in proteins (17-34% dry weight basis), minerals and vitamins (Ravindran and Ravindran, 1988). Cassava leaves proteins is rich in most of the essential amino acids except methionine and phenylalanine (Gomez et al., 1985; Rogers et al., 1963; Ross et al., 1969).
Cassava (Manihot esculenta Crantz) has leaves that are wide and palmated and ranges from 5 to 7 lobes.

They are carried by a long and thin petiole. Bunch of mature roots from 30 to 120 cm long and from 4 to 15 cm in diameters appear in the ground. The root is composed of two parts: the external part constitutes the skin and the internal part the pulp. Cassava roots are quantitatively the third most important food in the tropics, after rice and corn. Cassava roots and leaves constitute energy-rich and protein-rich foods respectively, for the populations in Central and West Africa, where they are consumed as staple foods (Kobawila et al., 2005). But cassava roots and leaves contain some cyanide in the form of cyanogenic glucosides, notably the linamarine, which can constitute a poison for the consumers when roots or leaves are processed improperly. Cassava roots and leaves processing in Congo, as in most Central African countries, and Nigeria in West Africa involve fermentation (Kobawila et al., 2005). The fermentation of the cassava roots is a lactic fermentation (pH 3.8) with Lactobacillus as dominant microflora whereas that of the cassava leaves is an alkaline fermentation (pH 8.5) where Bacillus constitute the main microflora (Kobawila et al., 2005). The hydrolysis of cyanogenic glucosides takes place as well in acid medium during the cassava tubers fermentation as in basic medium with the cassava leaves fermentation (Kobawila et al., 2005). The cyanide content decreases during the fermentation of cassava roots and leaves by more than 70% through the activities of the bacterial produced linamarase, allowing the hydrolysis of cyanogenic glucosides (Kobawila et al., 2005). Certain lactic bacteria present in the environment of fermentation are resistant to the strong cyanide concentrations of between 200 and 800 ppm (Kobawila et al., 2005).
But cassava roots and leaves are also rich in cyanide in the form of cyanogenic glucosides, linamarine and lotaustraline (Montgomery, 1980; Dunstan et al., 1996) in a ratio of 93:7 (Butler et al., 1965). Cassava is classified according to the cyanhydric acid content into 3 categories: I) Very toxic variety with more than 100 mg HCN/kg of pulp. II) Moderately toxic variety with 50-100 mg HCN/kg of pulp. III) Not toxic variety with less than 50 mg HCN/kg of pulp (Butler et al., 1965).

The hydrolysis of cyanogenic glucosides by the endogenous or microbial linamarase enzyme releases the cyanhydric acid, which is toxic (Howlett et al., 1990). Cyanogenic glucosides are thus responsible for the toxicity of unfermented roots and leaves of cassava (Howlett et al., 1990; Mlingi et al., 1991). Unhydrolysed linamarine, remaining in cassava roots and leaves after fermentation, can constitute a health problem for the consumers (Gomez et al., 1985; Cooke, 1978; Ikediobi et al., 1980; Nartley, 1968). Indeed, the chronic exposure to cyanide due to the consumption of non-detoxified cassava products is associated to a certain number of diseases inferred by the cyanide, including goitre, dwarfism and the Tropical Ataxic Neuropathy (Balagopalan et al., 1988). It is particularly a problem in the regions where cassava is the major source of calories (Tewe, 1984; Umoh et al., 1985). Cyanhidric acid is lethal at a consumption dose of 0.5 to 3.5 mg per kilogram body weight (Oke, 1980). Traditional technologies have been developed in Central Africa to eliminate cyanhydric acid in cassava roots and leaves, such that they are suitable for human consumption. “Bikedi” is a fermented cassava root food obtained by retting of cassava in Congo (Dunican, 1990; Lancaster et al., 1982; Ongusua et al., 1983), while “ntoba mbodi” is a vegetable obtained by semi-solid fermentation of cassava leaves, but in Nigeria cassava is fermented by steeping in water for a good number of days until it loses rigidity and can be squeezed in during making. The sensory characteristics (colour, texture, smell, taste) of the final products depend on the type of cassava roots and leaves, fermentation conditions and on the microorganisms involved (Dunican, 1990). Improvement of the traditional processes and quality control require a better understanding of the traditional fermentation process to obtain “bikedi, ntoba mbodi and fufu”.

Aim and Objectives
The aim of this research was to compare the effect of microalgae and other treatments on the cyanide content of fermented garri.

The specific objectives were;
I) To know whether the addition of microalgae during fermentation will reduce the cyanide content, of fermented cassava.
II) To compare the effect of microalgae and other treatments (e.g. Bitter Kola, lemon grass, and red oil) on the cyanide level of fermented garri.

Manihot esculenta, called cassava, is a woody shrub that originated from South America and belong to the spurge family known as euphorbiaceae (Fauquet and Fargette, 1990). It is normally cultivated as an annual crop in tropical and subtropical regions for its edible swolen roots that are rich in starch (carbohydrates). Cassava when dried to a powdery (or pearly) extract is called tapioca while its fermented, flaky version is named garri (Fauquet and Fargette, 1990).

Figure 1: Cassava tuber (Adams et al., 2009).
Cassava is the third largest source of carbohydrates in the tropics, after rice and maize and is a major staple food in the developing world especially among rural populace, providing a basic diet for over half a billion people (Fauquet and Fargette, 1990). It is a highly drought-tolerant crop capable of growing on marginal soils. Nigeria is the world’s largest producer of cassava, while Thailand is the largest exporter of dried cassava(Linley et al., 2002). There are two classes of cassava based on taste as either sweet or bitter. Like other roots and tubers, both bitter and sweet varieties of cassava contain ant nutrients and toxins of which the bitter varieties contain much larger amounts (Ravindran, 1992). Cassava tubers need to be properly prepared before consumption, as improper preparation can leave high level of residual cyanide which can cause acute cyanide intoxication, goiters and even ataxia or partial paralysis (Ravindran, 1992); inley et al., 2002). The more toxic varieties of cassava are utilized in times of famine in some places as a means of food security (Ravindran, 1992).Some rural farmers often prefer the bitter varieties because they deter pests, animals, and thieves (Linley et al., 2002).

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Scientific Classification
Kingdom: Plantae
Phylum: Angiosperms
Sub phylum: Eudicots
Super order: Rosids
Order: Malpighiales
Family: Euphorbiaceae
Subfamily: Crotonoideae
Tribe: Manihoteae
Genus: Manihot
Species: M. esculenta
Binomial name: Manihot esculenta.
(Linley et al., 2002).

The cassava root is long, tapered and swolen forming tuber. The tuber is a firm, homogeneous flesh covered with a detachable rind that is about 1 mm thick, it looks rough and brown on the outside. Commercial varieties can be 5 to 10 cm in diameter at the top, and around 15 to 30 cm long. A vascular bundle that appears to be woody runs along the root’s axis while the flesh can be chalk-white or yellowish (Ravindran, 1992). Cassava roots are very rich in starch and contain high amounts of calcium (50 mg/100g), phosphorus (40 mg/100g) and vitamin C (25 mg/100g). However, they are poor in protein,lipid andother nutrients. However, cassava leaves are a good source of proteins rich in lysine but deficient in the amino acid methionine and little tryptophan (Ravindran, 1992).

Wild populations of M. esculenta subspecies, flabellifolia which has shown to be the progenitor of domesticated cassava are centered in West-Central Brazil, where it was likely first domesticated more than 10,000 years BC(Olsen and Schaal, 1999). Different varieties of the domesticated species can also be seen growing in the wild in southern Brazil. By 4,600 BC, manioc pollen was first seen in the Gulf of Mexico lowlands (Pope et al., 2001). The oldest evidence of cassava cultivation comes from a 1,400-year-old Maya site in El Salvador (Pope et al., 2001). Cassava was a staple food for pre-Columbian peoples in the Americas and is often portrayed in indigenous art. Cassava having its high food potential, it had become a major food of the native populations of northern South America, southern Mesoamerica, and the Caribbean by the time of the Spanish conquest. Its cultivation was continued by the colonial Portuguese and Spanard (Pope et al., 2001). Cassava was introduced to Africa by Portuguese traders from Brazil in the 16th century. Maize and cassava are now important staple foods replacing native African crops (Adams et al., 2009). Cassava is sometimes described as the “bread of the tropics” (Adams et al., 2009).

Economic Importance and Production
World production of cassava tuber was estimated at 184 million tonnes in 2002, rising to 230 million tonnes in 2008(Adams et al., 2009). The majority of production in 2002 was in Africa, where 99.1 million tonnes were grown, but in Asia, 51.5 million tonnes were grown and 33.2 million tonnes were grown in Latin America and the Caribbean, specifically in Jamaica. Nigeria is the world’s largest producer of cassava (Pope et al., 2011). But based on the statistics from the FAO of the United Nations, Thailand was the largest exporter of dried cassava with a total of 77% of world export in 2005. The second-largest exporting country is Vietnam, with 13.6%, followed by Indonesia (5.8%) and Costa Rica (2.1%)(Adams et al., 2009).In 2010, the average yield of cassava crops worldwide was about 12.5 tonnes per hectare. The most productive cassava farms in the world were in India, with a nationwide average yield of 34.8 tonnes per hectare in 2010 (Pope et al., 2011). Cassava, yams and sweet potatoes are important sources of food in the tropics. The cassava plant gives the third-highest yield of carbohydrates per cultivated area among crop plants, after sugarcane and sugar beets (Stone, 2002). Cassava plays a particularly important role in agriculture in developing countries, especially in sub-Saharan Africa because it does well on poor soils and with low rainfall and because it is a perennial that can be harvested as required. Its wide harvesting window allows it to act as a famine reserve and is invaluable in managing labor schedules. It offers flexibility to resource-poor farmers because it serves as either a subsistence or a cash crop (Stone, 2002).

No continent depends as much on root and tuber crops in feeding its population more than Africa. In the humid and sub humid areas of tropical Africa, it is either a primary staple food or a secondary costaple (Stone, 2002). In Ghana, cassava and yams occupy an important position in the agricultural economy and contribute about 46% of the agricultural gross domestic product. Cassava accounts for a daily caloric intake of 30% in Ghana and is grown by nearly every farming family. The importance of cassava to many Africans is epitomized in the Ewe name for the plant, agbeli, meaning “there is life” (Stone, 2002). In the subtropical region of southern China, cassava is the fifth-largest crop in term of production, after rice, sweet potato, sugar cane and maize. China is also the largest export market for cassava produced in Vietnam and Thailand. Over 60% of cassava production in China is concentrated in a single province, Guangxi, averaging over 7 million tonnes annually (Frederick and Hog, 2008).According to the Food and Agriculture Organization’s corporate statistical database (FAOSTAT) the top 20 cassava producing countries by year 2012 were as shown in table 1 below:

Table 1: Top cassava producers of the world.
Rank Country Cassava Production MT
1 Nigeria 54 000 000
2 Thailand 29 848 000
3 Indonesia 24 177 372
4 Brazil 23 044 557
5 Rwanda 2 716 421
6 Ghana 14 547 279
7 Angola 10 636 400
8 Mozambique 10 051 364
9 Viet Nam 9 745 545
10 India 8 746 500
11 Cambodia 7 613 697
12 Benin 3 295 785
13 Uganda 4 924 560
14 Malawi 4 692 202
15 China 4 560 000
16 Cameroon 4 287 177
17 Sierra Leone 3 520 000
18 Madagascar 3 621 309
19 United Republic of Tanzania 5 462 454
20 Democratic Republic of the Congo 16 000 000
(Olumide, 2004).

Cassava Cultivation and Harvesting
Cassava is propagated by vegetative stem and is harvested by hand by pulling the lower part of the stem and raising the roots out of the ground then removing them from the base of the plant. The upper parts of the stems with the leaves are plucked off before harvest. Cassava is propagated by cutting the stem into sections of approximately 15 cm, these are being planted prior to the wet season (Reinhardt, 2011). 2.1.6 Post harvest handling and storage Cassava undergoes post harvest physiological deterioration (PPD) once the tubers are separated from the main plant. When the tubers are damaged, the normally respond with a healing mechanism by secreting coumaric acids. However, the same mechanism is initiated about 15 minutes after harvest and fails to switch off in harvested tubers (Zidenga, 2012). It continues until the entire tuber is oxidized and blackened within two to three days after harvest thereby rendering it unpalatable for use (Zidenga, 2012). Lately, work has indicated that PPD is related to the accumulation of reactive oxygen species (ROS) initiated by cyanide release during mechanical harvesting. According to this research, shelf life of cassava was increased to up to 2 weeks by overexpressing a cyanide insensitive alternative oxidase (Zidenga, 2012). PPD is one of the major limitations that is preventing farmers from exporting cassavas and generating much needed income. Fresh cassava can be preserved like potato using thiabendazole or bleach as a fungicide, then wrapping in plastic, coating in wax or freezing (Zidenga, 2012).

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Nutritional profile of Cassava Tuber
Cassava tuber is majorly a source of carbohydrate (Olumide, 2004). Its composition shows 60–65 percent moisture, 20–31 percent carbohydrate, 1–2 percent crude protein and a comparatively low content of vitamins and minerals (Olumide, 2004). On the other hand, the root has high calcium and vitamin C content and also contain a nutritionally significant quantity of thiamine, riboflavin and nicotinic acid. Cassava starch contains 70 % amylopectin and 20 % amylose. Cooked cassava starch has 75 percent digestibility (Olumide, 2004). The tuber also provides little protein without any known essential amino acids.
Cassava is a good source of nutrition in certain ecosystems because it is one of the most drought-tolerant crops and can be successfully cultivated on marginal soils. It gives reasonable yields where many other crops do not grow well. Cassava is well adapted within latitudes 30° north and south of the equator, at elevations between sea level and 2,000 m (6,600 ft) above sea level, in equatorial temperatures, with rainfalls from 50 mm to 5 m annually and to poor soils with a pH ranging from acidic to alkaline. These conditions are common in certain parts of Africa and South America (Olumide, 2004).
Cassava is a highly productive crop in terms of quantity of food produced per unit land area per unit of time, significantly higher than other staple crops. Cassava can produce food calories at rates exceeding 250,000 cal/hectare/day compared with 176,000 for rice, 110,000 for wheat, and 200,000 for maize (corn) (Olumide, 2004). However, cassava also has antinutritional and toxic factors. Of particular concern are the cyanogenic glucosides of cassava (linamarin and lotaustralin). On hydrolysis, these release hydrocyanic acid (HCN) (Olumide, 2004). The presence of cyanide in cassava is of concern for human and for animal consumption. The concentration of these ant nutritional and unsafe glycosides varies considerably between varieties and also with climatic and cultural conditions. Selection of cassava species to be grown, therefore, is quite important. Once harvested, bitter cassava must be treated and prepared properly prior to human or animal consumption, while sweet cassava can be used after simple boiling (Olumide, 2004).

In many countries, significant research has begun to evaluate the use of cassava as an ethanol, biofuel and feedstock. Under the Development Plan for Renewable Energy in the Eleventh Five-Year Plan in the People’s Republic of China, the target is to increase the application of ethanol fuel by nongrain feedstock to 2 million tonnes, and that of biodiesel to 200 thousand tonnes by 2010 (Cereda et al., 1996). This will be equivalent to a substitute of 10 million tonnes of petroleum. As a result, cassava (tapioca) chips have gradually become a major source for ethanol production (Cereda et al., 1996). On December 22, 2007, the largest cassava ethanol fuel production facility was completed in Beihai, with annual output of 200 thousand tons, which would need an average of 1.5 million tons of cassava (Cereda et al., 1996). In November 2008, China-based Hainan Yedao Group reportedly invested $51.5m (£31.8m) in a new biofuel facility that is expected to produce 33 million US gallons (120,000 m3) a year of bioethanol from cassava plants (Cereda et al., 1996).

Uses of Cassava
Alcoholic beverages made from cassava include Cauim and tiquira (Brazil), kasiri (Sub-Saharan Africa), Impala (Mozambique) masato (Peruvian Amazonia chicha), parakari or kari (Guyana), nihamanchi (South America) aka nijimanche (Ecuador and Peru), ö döi (chicha de yuca, Ngäbe-Bugle, Panama), sakurá (Brazil, Surinam)(Olumide, 2004).

Cassava-based dishes are widely consumed wherever the plant is cultivated; some have regional, national, or ethnic importance (Frederick and Hog, 2008). Cassava must be cooked properly to detoxify it before it is eaten (Frederick and Hog, 2008).Cassava can be cooked in many ways. The root of the sweet variety has a delicate flavor and can replace potatoes. It is used in cholent in some households. It can be made into a flour that is used in breads, cakes and cookies. In Brazil, detoxified manioc is ground and cooked to a dry, often hard or crunchy meal known as farofa used as a condiment, toasted in butter, or eaten alone as a side dish (Frederick and Hog, 2008).

Animal feed
Cassava tubers and hay are used worldwide as animal feed. Cassava hay is harvested at a young growth stage (three to four months) when it reaches about 30 to 45 cm (12 to 18 inch.) above ground; it is then sun-dried for one to two days until it has final dry matter content of less than 85%. Cassava hay contains high protein (20–27% crude protein) and condensed tannins (1.5–4% CP). It is valued as a good roughage source for ruminants such as cattle (EFSA Panel, 2004).



Laundry starch Manioc is also used in a number of commercially available laundry products, especially as starch for shirts and other garments. Using manioc starch diluted in water and spraying it over fabrics before ironing helps stiffen collars.

Medicinal use
According to the American Cancer Society, cassava is ineffective as an anti-cancer agent: “there is no convincing scientific evidence that cassava or tapioca is effective in preventing or treating cancer” (Bhatia, 2002).

Food use processing and toxicity
Cassava roots, peels and leaves should not be consumed raw because they contain two cyanogenic glucosides, linamarin and lotaustralin. These are decomposed by linamarase, a naturally occurring enzyme in cassava, liberating hydrogen cyanide (HCN) (Bhatia, 2002). Cassava varieties are often categorized as either sweet or bitter, signifying the absence or presence of toxic levels of cyanogenic glucosides, respectively. The so-called sweet (actually not bitter) cultivars can produce as little as 20 milligrams of cyanide (CN) per kilogram of fresh roots, whereas bitter ones may produce more than 50 times as much (1 g/kg). Cassavas grown during drought are especially high in these toxins (Aregheore and Agunbiade, 1991; White et al., 1998). A dose of 25 mg of pure cassava cyanogenic glucoside, which contains 2.5 mg of cyanide, is sufficient to kill a rat (EFSA Panel, 2004). Excess cyanide residue from improper preparation is known to cause acute cyanide intoxication, and goiters, and has been linked to ataxia (a neurological disorder affecting the ability to walk, also known as konzo). It has also been linked to tropical calcific pancreatitis in humans, leading to chronic pancreatitis (Bhatia, 2002).

In Africa, a previous issue was the cassava mealybug (Phenacoccus manihoti) and cassava green mite (Mononychellus tanajoa). These pests can cause up to 80% crop loss, which is extremely detrimental to the production of subsistence farmers (Morante et al., 2010). These pests were rampant in the 1970s and 1980s but were brought under control following the establishment of the “Biological Control Centre for Africa” of the International Institute of Tropical Agriculture (IITA) under the leadership of Hans Rudolf Herren (Morante et al., 2010). The Centre investigated biological control for cassava pests; two South American natural enemies Apoanagyrus lopezi (a parasitoid wasp) and Typhlodromalus aripo (a predatory mite) were found to effectively control the cassava mealybug and the cassava green mite, respectively (Morante et al., 2010). The African cassava mosaic virus causes the leaves of the cassava plant to wither, limiting the growth of the root (Morante et al., 2010). An outbreak of the virus in Africa in the 1920s led to a major famine. The virus is spread by the whitefly and by the transplanting of diseased plants into new fields. Sometime in the late 1980s, a mutation occurred in Uganda that made the virus even more harmful, causing the complete loss of leaves. This mutated virus spread at a rate of 50 mi (80 km) per year, and as of 2005 was found throughout Uganda, Rwanda, Burundi, the Democratic Republic of the Congo and the Republic of the Congo (Morante et al., 2010).Cassava brown streak virus disease has been identified as a major threat to cultivation worldwide (McSorley et al., 1983)
A wide range of plant parasitic nematodes have been reported associated with cassava worldwide.

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These include Pratylenchus brachyurus, Rotylenchulus reniformis, Helicotylenchus spp., Scutellonema spp. and Meloidogyne spp., of which Meloidogyne incognita and Meloidogyne javanica are the most widely reported and economically important (McSorley et al., 1983). Meloidogyne spp. feeding produces physically damaging galls with eggs inside them. Galls later merge as the females grow and enlarge, and they interfere with water and nutrient supply (McSorley et al., 1983). Cassava roots become tough with age and restrict the movement of the juveniles and the egg release. It is therefore possible that extensive galling can be observed even at low densities following infection (McSorley et al., 1983). Other pest and diseases can gain entry through the physical damage caused by gall formation, leading to rots. They have not been shown to cause direct damage to the enlarged storage roots, but plants can have reduced height if there was loss of enlarged root weight (McSorley et al., 1983). Research on nematode pests of cassava is still in the early stages; results on the response of cassava is, therefore, not consistent, ranging from negligible to seriously damaging (Caveness, 1992). Since nematodes have such a seemingly erratic distribution in cassava agricultural fields, it is not easy to clearly define the level of direct damage attributed to nematodes and thereafter quantify the success of a chosen management method (Gapasin, 1980). The use of nematicides has been found to result in lower numbers of galls per feeder root compared to a control, coupled with a lower number of rots in the storage roots (Coyne, 1994). The organophosphorus nematicide femaniphos, when used, did not affect crop growth and yield parameter variables measured at harvest. Nematicide use in cassava is neither practical nor sustainable; the use of tolerant and resistant varieties is the most practical and sustainable management method (Gapasin, 1980).

A cyanide is any chemical compound that contains monovalent combining group CN (Jones, 1998). This group, known as the cyanogroup, consists of a carbon atom triple-bonded to a nitrogen atom (Greenwood and Earnshaw, 1997).In inorganic cyanides, such as sodium cyanide and potassium cyanide this group is present as the negatively charged polyatomiccyanideion (CN−); these compounds, which are regarded as salts of hydrocyanic acid, are highly toxic (Greenwood and Earnshaw, 1997). The cyanide ion is isoelectronic with carbon monoxide and with molecular nitrogen (Miessler and Tarr, 2004).Organic cyanides are usually called nitriles; in these, the CN group is linked by a covalent bond to a carbon-containing group, such as methyl (CH3) in methyl cyanide (acetonitrile). Because they do not release cyanide ions, nitriles are generally less toxic, or in the case of insoluble polymers such as acrylic fiber, essentially nontoxic unless burned(Miessler and Tarr, 2004).Hydrocyanic acid, also known as hydrogen cyanide, or HCN, is a highly volatile liquid used to prepare acrylonitrile, which is used in the production of acrylic fibers, synthetic rubber, and plastics (Vetter, 2005). Cyanides are employed in a number of chemical processes, including fumigation, case hardening of iron and steel, electroplating, and the concentration of ores. In nature, substances yielding cyanide are present in certain seeds, such as the pit of the cherry and the seeds of apples (Vetter, 2005).

Nomenclature and Etymology
In IUPAC nomenclature, organic compounds that have a –C≡N functional group are called nitriles. Thus, nitriles are organic compounds (Pieniazek et al., 2005). An example of a nitrile is CH3CN, acetonitrile, also known as methyl cyanide. Nitriles usually do not release cyanide ions. A functional group with a hydroxyl and cyanide bonded to the same carbon is called cyanohydrin. Unlike nitriles, cyanohydridins do release hydrogen cyanide. In inorganic chemistry, salts containing the C≡N− ion are referred to as cyanides (Pieniazek et al., 2005).The word is derived from the Greek kyanos, meaning dark blue, as a result of its being first obtained by the heating of the pigment known as Prussian blue (Vetter, 2005).

Occurrence and reactions
In nature Cyanides are produced by certain bacteria, fungi, and algae and are found in a number of plants. Cyanides are found in substantial amounts in certain seeds and fruit stones, e.g., those of apricots, apples, and peaches(Pieniazek et al., 2005). In plants, cyanides are usually bound to sugar molecules in the form of cyanogenic glycosides and defend the plant against herbivores. Cassava roots (also called manioc), an important potato-like food grown in tropical countries (and the base from which tapioca is made), also contain cyanogenic glycosides (Pieniazek et al., 2005).
The Madagascar bamboo Cathariostachys madagascariensis produces cyanide as a deterrent to grazing. In response, the golden bamboo lemur, which eats the bamboo, has developed a high tolerance to cyanide (Pieniazek et al., 2005).

Interstellar medium
The cyanide radical CN• has been identified in interstellar space (Pieniazek et al., 2005). The cyanide radical (called cyanogen) is used to measure the temperature of interstellar gas clouds (Roth et al., 1993).

Pyrolysis and combustion product
Hydrogen cyanide is produced by the combustion or pyrolysis of certain materials under oxygen-deficient conditions. For example, it can be detected in the exhaust of internal combustion engines and tobacco smoke. Certain plastics, especially those derived from acrylonitrile, release hydrogen cyanide when heated or burnt (Anon, 2004).

Coordination chemistry The cyanide anion is a ligand for many transition metals (Sharpe, 1976). The high affinities of metals for this anion can be attributed to its negative charge, compactness, and ability to engage in π-bonding. Well-known complexes include:
• Hexacyanides [M(CN)6]3− (M = Ti, V, Cr, Mn, Fe, Co), which are octahedral in shape.
• The tetracyanides, [M(CN)4]2− (M = Ni, Pd, Pt), which are square planar in their geometry;
• The dicyanides [M(CN)2]− (M = Cu, Ag, Au), which are linear in geometry(Sharpe, 1976).
Among the most important cyanide coordination compounds are the octahedrally coordinated compounds potassium ferrocyanide and the pigment Prussian blue, which are both essentially non toxic due to the tight binding of the cyanides to a central iron atom (Holleman and Wiberg, 2001). Prussian blue was first accidentally made around 1706, by heating substances containing iron and carbon and nitrogen, and other cyanides made subsequently (and named after it). Among its many uses, Prussian blue gives the blue color to blueprints, bluing, and cyanotypes (Holleman and Wiberg, 2001).The enzymes called hydrogenases contain cyanide ligands attached to iron in their active sites. The biosynthesis of cyanide in the [NiFe]-hydrogenases proceeds from carbamoyl phosphate, which converts to cysteinylthiocyanate, the CN− donor (Reissmann et al., 2003).

Organic derivatives
Because of the cyanide anion’s high nucleophilicity, cyano groups are readily introduced into organic molecules by displacement of a halide group (e.g., the chloride on methyl chloride). In general, organic cyanides are called nitriles. Thus, CH3CN can be called methyl cyanide but more commonly is referred to as acetonitrile. In organic synthesis, cyanide is a C-1 synthon; i.e., it can be used to lengthen a carbon chain by one, while retaining the ability to be functionalized (Andrussow, 1927).

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