Cassava

Cassava Leaves
A manioc tuber
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
Order:	Malpighiales
Family:	Euphorbiaceae
Subfamily:	Crotonoideae
Tribe:	Manihoteae
Genus:	Manihot
Species:	M. esculenta
Binomial name
Manihot esculenta Crantz

Cassava (Manihot esculenta), also called yuca or manioc, is a woody shrub of the Euphorbiaceae (spurge family) native to South America. Cassava is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy tuberous root, a major source of carbohydrates. Nigeria is the world's largest producer of cassava.
Cassava is the third-largest source of carbohydrates for meals in the world.^[1][2] Cassava is classified as sweet or bitter depending on the level of toxic cyanogenic glucosides; improper preparation of bitter cassava causes a disease called konzo. Nevertheless, farmers often prefer the bitter varieties because they deter pests, animals, and thieves.^[3]
Cassava is sometimes spelled cassaba or cassada.^[4] In English-language publications, the plant may be occasionally called by local names, such as mandioca, aipim, or macaxeira (Brazil), yuca (Bolivia, Colombia, Cuba, Ecuador, the Dominican Republic, Haiti, Panama, Peru, Puerto Rico, Venezuela), mandi´o (Paraguay), akpu, ege or ugburu (Nigeria), bankye (Ghana), mogo or mihogo (Swahili-speaking Africa), pondu in (Lingala-speaking Africa), kappa (India), maniokka (Sri Lanka), singkong (Indonesia), ubi kayu (Malaysia), kamoteng kahoy or balanghoy (Philippines), mushu (China), man sampalang (Thailand), củ sắn or khoai mì (Vietnam), and manioke , tapioka or manioka (Polynesia).^[5]

Contents 1 Description 2 History 3 Economic impact 4 Uses 4.1 Culinary 4.2 Biofuel 4.3 Animal feed 4.4 Ethnomedicine 5 Food use processing and toxicity 6 Farming 6.1 Harvesting 6.2 Postharvest handling and storage 6.3 Pests

Description

Unprocessed cassava roots

The cassava root is long and tapered, with a firm homogeneous flesh encased in a detachable rind, about 1mm thick, rough and brown on the outside. Commercial varieties can be 5 to 10 cm in diameter at the top, and around 15 cm to 30 cm long. A woody cordon runs along the root's axis. The flesh can be chalk-white or yellowish. Cassava roots are very rich in starch, and contain significant amounts of calcium (50 mg/100g), phosphorus (40 mg/100g) and vitamin C (25 mg/100g). However, they are poor in protein and other nutrients. In contrast, cassava leaves are a good source of protein and rich in the amino acid lysine, though deficient in methionine and possibly tryptophan.^[6]

History

Yuca. Moche Culture. 100 A.D. Larco Museum Collection.

Wild populations of M. esculenta subspecies flabellifolia, shown to be the progenitor of domesticated cassava, are centered in west-central Brazil where it was likely first domesticated no more than 10,000 years BP.^[7] By 6,600 BC, manioc pollen appears in the Gulf of Mexico lowlands, at the San Andrés archaeological site.^[8] The oldest direct evidence of cassava cultivation comes from a 1,400 year old Maya site, Joya de Cerén, in El Salvador.^[9] although the species Manihot esculenta likely^{[weasel words]} originated^{[citation needed]} further south in Brazil and Paraguay. With its high food potential, it had become a staple food of the native populations of northern South America, southern Mesoamerica, and the Caribbean by the time of the Spanish conquest, and its cultivation was continued by the colonial Portuguese and Spanish. Forms of the modern domesticated species can be found growing in the wild in the south of Brazil. While there are several wild Manihot species, all varieties of M. esculenta are cultigens.
Cassava was a staple food for pre-Columbian peoples in the Americas, and is often portrayed in indigenous art. The Moche people often depicted yuca in their ceramics.^[10]
Since being introduced by Portuguese traders from Brazil in the 16th century, maize and cassava have replaced traditional African crops as the continent’s most important staple food crops.^[11] Cassava is sometimes described as the ‘bread of the tropics'.^[12]

Economic impact

Cassava output in 2005

World production of cassava root was estimated to be 184 million tonnes in 2002, rising to 230 million tonnes in 2008. (FAO). The majority of production in 2002 was in Africa where 99.1 million tonnes were grown. 51.5 million tonnes were grown in Asia and 33.2 million tonnes in Latin America and the Caribbean. Nigeria is the world's largest producer of cassava. However, based on the statistics from the FAO of the United Nations, Thailand is the largest exporting country 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%). Worldwide cassava production increased by 12.5% between 1988 and 1990.^{[citation needed]}
Cassava, together with yams (Dioscorea sp.) and sweet potatoes (Ipomea batatas) are important sources of food in the tropics. The cassava plant gives the highest yield of food energy per cultivated area per day among crop plants, except possibly for sugarcane.^{[citation needed]} Cassava plays a particularly important role in developing countries' farming—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 also offers flexibility to resource-poor farmers because it serves as either a subsistence or a cash crop.^[13]

Cassava in cultivation in Democratic Republic of Congo

While underground storage of cassava is advantageous for managing work schedules, it may also lead to reduced quality of the roots, sometimes leaving the roots unsuitable for many types of processing. In some areas farmers have come to increasingly rely on dried Cassava chips. A 1992 study (Nweke et al.) revealed that about 42% of harvested cassava roots in West and East Africa are processed into dried chips and flour.^{[citation needed]}
No continent depends as much on root and tuber crops in feeding its population as does Africa. In the humid and sub-humid areas of tropical Africa, cassava is either a primary staple food or a secondary co-staple. In Ghana, for example, Cassava and yams occupy an important position the agricultural economy and contribute about 46% of the agricultural Gross Domestic Product (GDP). Cassava accounts for a daily calorie intake of 30% in Ghana and is grown by nearly every farming family. The importance of cassava to many Africans is epitomised in the Ewe (a language spoken in Ghana, Togo and Benin) name for the plant, agbeli, meaning "there is life." However, the price of cassava has risen significantly in the last half decade and lower-income people have turned to other carbohydrate-rich foods such as rice.^{[citation needed]}
In Tamil Nadu, one of the 28 states of India, the National Highway 68 between Thalaivasal and Attur has many cassava processing factories (local name Sago Factory) alongside it—indicating an abundance of it in the neighborhood. Cassava is widely cultivated and eaten as a staple food in Andhra Pradesh and in Kerala.
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 seven million tons annually.

Uses

Cassava heavy cake

Culinary

Cassava-based dishes are widely consumed wherever the plant is cultivated. Some of these dishes have regional, national, or ethnic importance.^[14] Cassava must be cooked properly to detoxify it before it is eaten.
Cassava can be cooked in various ways. The soft-boiled root has a delicate flavor and can replace boiled potatoes in many uses: as an accompaniment for meat dishes, or made into purées, dumplings, soups, stews, gravies, etc. Deep fried (after boiling or steaming), it can replace fried potatoes, with a distinctive flavor. Foufou is made from the starchy cassava-root flour. Tapioca (or fecula) is an essentially flavourless starchy ingredient produced from treated and dried cassava (manioc) root and used in cooking. It is similar to sago and is commonly used to make a milky pudding similar to rice pudding. Boba tapioca pearls are made from cassava root. It is also used in cereals for which several tribes in South America have used it extensively. It is also used in making cassava cake, a popular pastry. Cassava is used in making eba a popular food in Nigeria. Gari soakings is a delicacy in Ghana that cost less than 1USD. You simply soak gari in cold water, add a bit of sugar and roasted groundnut to taste, a quantity of evaporated milk of your choice. Gari soakings when prepared with coconnut water with a cube of sugar with same ingredients tastes better.
The juice of the bitter cassava, boiled to the consistency of thick syrup and flavored with spices, is called cassareep. It is used as a basis for various sauces and as a culinary flavoring, principally in tropical countries. It is exported chiefly from Guyana.
The leaves can be pounded to a fine chaff and cooked as a palaver sauce in Sierra Leone, usually with palm oil but vegetable oil can also be used. Palaver sauces contain meat and fish as well. It is necessary to wash the leaf chaff several times to remove the bitterness.

Fried cassava in Indonesia

In DR Congo, the leaves are used in a stew called Pondu in Lingala, Sombe in Swahili and Sakasaka in Kikongo. The cassava root flour is also used to make a cassava bread from boiling enough flour until it is a thick rubbery ball called Bukari in Swahili, and Luku in Kikongo. This cassava bread is often affectionately known as "La boule Nationale" (the national ball) in French. The flour is also made into a paste and fermented before boiling after wrapping in banana or other forest leaves. This fermented state is called chikwangue in French and kwanga or nkwanga in Lingala and Kikongo. This last form has a long shelf life and is a preferred food to take on long trips where refrigeration is not possible.
Cassava was also used to make alcoholic beverages. The English explorer and naturalist Charles Waterton reported in Wanderings in South America (1836) that the natives of Guyana used cassava to make liquor, which they abandoned when rum became available.^[15] Hamilton Rice, in 1913, also remarked on liquor being made from cassava in the Brazilian rainforest.^[16]
The Indian tribes in northern Brazil and Surinam – Tiriós and Erwarhoyanas – make a beverage called "sakurá" with the sweet manioc variety of cassava named Yuca. It is the same beverage made by the Jivaro in Ecuador and Peru (the Shuara, Achuara, Aguaruna and Mayna people); they call it "nijimanche". As Michael Harner^[17] describes it:

The sweet manioc beer (nihamanci or nijiamanchi), is prepared by first peeling and washing the tubers in the stream near the garden. Then the water and manioc are brought to the house, where the tubers are cut up and put in a pot to boil. … The manioc is then mashed and stirred to a soft consistency with the aid of a special wooden paddle. While the woman stirs the mash, she chews handfuls of and spits them back into the pot, a process that may take half an hour or longer.

After the mash has been prepared it is transferred to a beer storage jar and left to ferment. … The resultant liquid tastes somewhat like a pleasingly alcoholic buttermilk and is most refreshing. The Jivaros consider it to be far superior to plain water, which they drink only in emergencies.^[18]

Biofuel

In many countries, significant research has begun to evaluate the use of cassava as an ethanol biofuel 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 non-grain feedstock to 2 million tonnes, and that of bio-diesel to 200 thousand tonnes by 2010. 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.^[19] On December 22, 2007, the largest cassava ethanol fuel production facility was completed in Beihai with annual output of two hundred thousand tons, which would need an average of one and half million tons of cassava.^[20] 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 gallons a year of bio-ethanol from cassava plants.^[21]

Animal feed

Cassava is used worldwide for animal feed as well. Cassava hay is produced at a young growth stage, 3–4 months, harvested about 30–45 cm above ground, and sun-dried for 1–2 days until it has final dry matter of at least 85%. The cassava hay contains high protein content (20-27% Crude Protein) and condensed tannins (1.5-4% CP). It is used as a good roughage source for dairy, beef, buffalo, goats, and sheep by either direct feeding or as a protein source in the concentrate mixtures.

Ethnomedicine

• The bitter variety
• The leaves are used to treat hypertension, headache, and pain.
• Cubans commonly use cassava to treat irritable bowel syndrome, the paste eaten in excess during treatment.^{[citation needed]}
• As cassava is a gluten-free natural starch, there have been increasing incidences of its appearance in Western cuisine as a wheat alternative for sufferers of celiac disease.

Food use processing and toxicity

Cassava root, peeled.

Cassava roots 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).^[22] Cassava varieties are often categorized as either sweet or bitter, signifying the absence or presence of toxic levels of cyanogenic glucosides. 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.^[23][24] A dose of 40 mg of pure cassava cyanogenic glucoside is sufficient to kill a cow. It can also cause severe calcific pancreatitis in humans, leading to chronic pancreatitis.
Societies that traditionally eat cassava generally understand that some processing (soaking, cooking, fermentation, etc.) is necessary to avoid getting sick.^{[citation needed]}
"Chronic, low-level cyanide exposure is associated with the development of goiter and with tropical ataxic neuropathy, a nerve-damaging disorder that renders a person unsteady and uncoordinated. Severe cyanide poisoning, particularly during famines, is associated with outbreaks of a debilitating, irreversible paralytic disorder called Konzo and, in some cases, death. The incidence of Konzo and tropical ataxic neuropathy can be as high as 3 percent in some areas."^[25]

Cassava bread

For some smaller-rooted sweet varieties, cooking is sufficient to eliminate all toxicity. The cyanide is carried away in the processing water and the amounts produced in domestic consumption are too small to have environmental impact.^[22] The larger-rooted bitter varieties used for production of flour or starch must be processed to remove the cyanogenic glucosides. and then ground into flour, which is then soaked in water, squeezed dry several times, and toasted. The starch grains that float to the surface during the soaking process are also used in cooking.^[26] The flour is used throughout South America and the Caribbean. Industrial production of cassava flour, even at the cottage level, may generate enough cyanide and cyanogenic glycosides in the effluents to have a severe environmental impact.^[22]
A safe processing method used by the pre-Columbian indigenous people of the Americas is to mix the cassava flour with water into a thick paste and then let it stand in the shade for five hours in a thin layer spread over a basket. In that time about 5/6 of the cyanogenic glycosides are broken down by the linamarase; the resulting hydrogen cyanide escapes to the atmosphere, making the flour safe for consumption the same evening.^[27]
The traditional method used in West Africa is to peel the roots and put them into water for 3 days to ferment. The roots then are dried or cooked. In Nigeria and several other west African countries, including Ghana, Benin, Togo, Ivory Coast, and Burkina Faso, they are usually grated and lightly fried in palm oil to preserve them. The result is a foodstuff called gari. Fermentation is also used in other places such as Indonesia (see Tapai). The fermentation process also reduces the level of antinutrients, making the cassava a more nutritious food.^[28]
The reliance on cassava as a food source and the resulting exposure to the goitrogenic effects of thiocyanate has been responsible for the endemic goiters seen in the Akoko area of southwestern Nigeria.^[29]
People dependent on cassava risk cyanide poisoning and malnutrition diseases such as kwashiorkor and endemic goiter.

Farming

Spreading cassava chips to dry, Democratic Republic of the Congo

Harvesting

Cassava is harvested by hand by raising the lower part of the stem and pulling 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 being planted prior to the wet season.^{[citation needed]}

Postharvest handling and storage

Cassava undergoes postharvest physiological deterioration, or PPD, once the tubers are separated from the main plant. The tubers, when damaged, normally respond with a healing mechanism. However, the same mechanism, which involves coumaric acids, initiates about 15 minutes after damage, and fails to switch off in harvested tubers. It continues until the entire tuber is oxidized and blackened within two to three days after harvest, rendering it unpalatable and useless.
PPD is one of the main obstacles currently preventing farmers from exporting cassavas abroad and generating income. Cassava can be preserved in various ways such as coating in wax or freezing.^{[citation needed]}

Frozen cassava leaves from the Philippines sold at a Los Angeles market

The major cause of losses during cassava chip storage is infestation by insects. A wide range of species that feed directly on the dried chips have been reported as the cause of weight loss in the stored produce. Some loss assessment studies and estimations on dried cassava chips have been carried out in different countries. Hiranandan and Advani (1955) measured 12 - 14% post-harvest weight losses in India for chips stored for about five months. Killick (1966) estimated for Ghana that 19% of the harvest cassava roots are lost annually, and Nicol (1991) estimated a 15 - 20% loss of -dried chips stored for eight months. Pattinson (1968) estimated for Tanzania a 12% weight loss of cassava chips stored for five months, and Hodges et al. (1985) assessed during a field survey post-harvest losses of up to 19% after 3 months and up to 63% after four to five months due to the infestation of Prostephanus truncatus (Horn). In Togo, Stabrawa (1991) assessed post-harvest weight losses of 5% after one month of storage and 15% after three months of storage due to insect infestation, and Compton (1991) assessed weight losses of about 9% for each store in the survey area in Togo. Wright et al. (1993) assessed post-harvest losses of chips of about 14% after four months of storage, about 20% after seven month of storage and up to 30% when P. truncatus attacked the dried chips. In addition, Wright et al. (1993) estimated that about 4% of the total national cassava production in Togo is lost during the chip storage. This was about equivalent to 0.05% of the GNP in 1989.
Plant breeding has resulted in cassava that is tolerant to PPD. Sánchez et al.^[30] identified four different sources of tolerance to PPD. One comes from the only Manihot species native of the United States (M. walkerae). A second source was induced by mutagenic levels of gamma rays which putatively silenced one of the genes involved in PPD genesis. A third source was a group of high-carotene clones. It is postulated that the antioxidant properties of carotenoids protects the roots from PPD (basically an oxidative process). Finally tolerance was also observed in a waxy-starch (amylose-free) mutant. It is expected that tolerance to PPD co-segregated with the starch mutation and is not a pleiotropic effect of the latter.

Pests

Main article: List of cassava diseases

In Africa the cassava mealybug (Phenacoccus manihoti) and cassava green mite (Mononychellus tanajoa) can cause up to 80% crop loss, which is extremely detrimental to the production of subsistence farmers. 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 IITA. 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.
The cassava mosaic virus causes the leaves of the cassava plant to wither, limiting the growth of the root. The virus caused a major African famine in the 1920s.^[31] 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 has been spreading at a rate of 50 miles per year, and as of 2005 may be found throughout Uganda, Rwanda, Burundi, the Democratic Republic of the Congo and the Republic of the Congo.^[32]
Recently, Brown Streak Disease has been identified as a major threat to Cassava cultivation worldwide.^[31]