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Yam (vegetable)
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For the vegetable sometimes called yam in the United States, see sweet potato. For the vegetable called yam in New Zealand, see Oxalis tuberosa.
Yam is the common name for some plant species in the genus Dioscorea (family Dioscoreaceae) that form edible tubers.[1] Yams are perennial herbaceous vines cultivated for the consumption of their starchy tubers in many temperate and subtropical world regions.[1] The tubers themselves are also called "yams", having numerous cultivars and related species.[1]
In parts of the United States and Canada, "yam" is sometimes used to refer to varieties of the unrelated sweet potato (Ipomoea batatas).
Contents
[hide]
1 Etymology
1.1 Other uses of the term yam
2 Description
3 Cultivation
3.1 Major cultivars
3.1.1 D. rotundata and D. cayenensis
3.1.2 D. alata
3.1.3 D. polystachya
3.1.4 D. bulbifera
3.1.5 D. esculenta
3.1.6 D. dumetorum
3.1.7 D. trifida
4 Harvesting
5 Production
6 Storage
7 Nutritional value
8 Phytochemicals
9 Comparison to other staple foods
10 Consumption
10.1 Africa
10.2 Philippines and Costa Rica
10.3 Vietnam
10.4 Indonesia
10.5 Japan
10.6 India
10.7 Nepal
10.8 Fiji Islands
10.9 The West
11 Toxicity
12 Cultural aspects
12.1 Nigeria and Ghana
12.1.1 New Yam Festival
12.2 Other
13 References
14 External links
Etymology[edit]
The name, yam, appears to derive from Portuguese inhame or Canarian (Spain) ñame, which are probably derived from West African languages.[2] The main derivations borrow from verbs meaning "to eat".[2]
Yams at a retail market
Other uses of the term yam[edit]
Several other unrelated root vegetables are sometimes referred to as "yams",[1] including:
Sweet potato (Ipomoea batatas), especially those with orange flesh, are often referred to as "yams" in the United States.[3] Today, the U.S. Department of Agriculture requires[4] sweet potatoes labeled with the term "yam" to be accompanied by the term "sweet potato".
Purple sweet potatoes in Okinawa.
Oca (Oxalis tuberosa) in New Zealand is typically referred to as "yam".[5][6]
Konjac corms - a Japanese vegetable with similar uses - is often colloquially referred to as a "yam",[7] although it is unrelated.
Taro in Malaysia and Singapore is referred to as "yam".[8]
Yam has various common names across multiple world regions.[1]
Description[edit]
Yam
A monocot related to lilies and grasses, yams are a vigorous herbaceous vine, providing an edible tuber.[1] Yams are also an invasive plant, often considered a "noxious weed", outside cultivated areas.[1] Native to Africa and Asia, yam tubers vary in size from that of a small potato to over 60 kg (130 lb). Some 870 species of yams are known,[1] and 95% of these crops are grown in Africa.[9]
Yam tubers can grow up to 15 m (49 ft) in length and 7.6 to 15.2 cm (3.0 to 6.0 in) high.[1] The tuber may grow into the soil up to 1.5 metres (4.9 ft) deep.[1] The plant disperses by seed.[1] Its origin is Southeast Asia and is grown throughout the tropics and temperate regions of the world.[1]
The edible tuber has a rough skin difficult to peel, but softens after heating. The skins vary in color from dark brown to light pink. The majority of the vegetable is composed of a much softer substance known as the "meat". This substance ranges in color from white or yellow to purple or pink in mature yams.
Cultivation[edit]
Yam crop begins when whole seed tubers or tuber portions are planted into mounds or ridges, at the beginning of the rainy season. The crop yield depends on how and where the setts are planted, sizes of mounds, interplant spacing, provision of stakes for the resultant plants, yam species, and tuber sizes desired at harvest. Small-scale farmers in West and Central Africa often intercrop yams with cereals and vegetables. The seed yams are perishable and bulky to transport. Farmers who do not buy new seed yams, usually set aside up to 30% of their harvest for planting the next year. Yam crops face pressure from a range of insect pests and fungal and viral diseases, as well as nematode. Their growth and dormant phases correspond respectively to the wet season and the dry season. For maximum yield, the yams require a humid tropical environment, with an annual rainfall over 1500 mm distributed uniformly throughout the growing season. White, yellow, and water yams typically produce a single large tuber per year, generally weighing 5 to 10 kg (11 to 22 lb).[10]
Despite the high labor requirements and production costs, consumer demand for yam is high in certain subregions of Africa,[1] making yam cultivation quite profitable to certain farmers.
Major cultivars[edit]
Purple yam freshly harvested and sliced for cross-sectional view
Many cultivars of yams are found throughout the humid tropics.[1] The most economically important are discussed below.[10]
D. rotundata and D. cayenensis[edit]
Dioscorea rotundata, the white yam, and D. cayenensis, the yellow yam, are native to Africa. They are the most important cultivated yams. In the past, they were considered as two separate species, but most taxonomists now regard them as the same species. Over 200 varieties between them are cultivated.
White yam tuber is roughly cylindrical in shape, the skin is smooth and brown, and the flesh is usually white and firm. Yellow yam has yellow flesh, caused by the presence of carotenoids. It looks similar to the white yam in outer appearance; its tuber skin is usually a bit firmer and less extensively grooved. The yellow yam has a longer period of vegetation and a shorter dormancy than white yam.
The 'Kokoro' variety is important in making dried yam chips.[11]
They are large plants; the vines can be as long as 10 to 12 m (33 to 39 ft). The tubers most often weigh about 2.5 to 5 kg (5.5 to 11.0 lb) each, but can weigh as much as 25 kg (55 lb). After 7 to 12 months' growth, the tubers are harvested. In Africa, most are pounded into a paste to make the traditional dish of "pounded yam," known as Fufu.[12]
D. alata[edit]
Water yam (D. alata)
D. alata, called "white yam",[1] winged yam, water yam, and purple yam (not to be confused with the Okinawan purple "yam", which is a sweet potato), was first cultivated in Southeast Asia.[1] Although not grown in the same quantities as the African yams, it has the largest distribution worldwide of any cultivated yam, being grown in Asia, the Pacific islands, Africa, and the West Indies.[1][13] Even in Africa, the popularity of water yam is second only to white yam. The tuber shape is generally cylindrical, but can vary. Tuber flesh is white and watery in texture.
Uhi was brought to Hawaii by the early Polynesian settlers and became a major crop in the 19th century when the tubers were sold to visiting ships as an easily stored food supply for their voyages.[14]
D. polystachya[edit]
Segment of a Chinese yam
D. polystachya, Chinese yam, is native to China. The Chinese yam plant is somewhat smaller than the African, with the vines about 3 m (9.8 ft) long. It is tolerant to frost and can be grown in much cooler conditions than other yams. It is also grown in Korea and Japan.
It was introduced to Europe in the 19th century, when the potato crop there was falling victim to disease, and is still grown in France for the Asian food market.
The tubers are harvested after about 6 months of growth. Some are eaten right after harvesting and some are used as ingredients for other dishes, including noodles, and for traditional medicines.[12]
D. bulbifera[edit]
Air potato
Wild yams
D. bulbifera, the air potato, is found in both Africa and Asia, with slight differences between those found in each place. It is a large vine, 6 m (20 ft) or more in length. It produces tubers, but the bulbils which grow at the base of its leaves are the more important food product. They are about the size of potatoes (hence the name "air potato"), weighing from 0.5 to 2.0 kg (1.1 to 4.4 lb).
Some varieties can be eaten raw, while some require soaking or boiling for detoxification before eating. It is not grown much commercially since the flavor of other yams is preferred by most people. However, it is popular in home vegetable gardens because it produces a crop after only four months of growth and continues producing for the life of the vine, as long as two years. Also, the bulbils are easy to harvest and cook.[12]
In 1905, the air potato was introduced to Florida and has since become an invasive species in much of the state. Its rapid growth crowds out native vegetation and is very difficult to remove since it can grow back from the tubers, and new vines can grow from the bulbils even after being cut down or burned.[15]
D. esculenta[edit]
Wild bitter yam vines
D. esculenta, the lesser yam, was one of the first yam species cultivated. It is native to Southeast Asia and is the third-most commonly cultivated species there, although it is cultivated very little in other parts of the world. Its vines seldom reach more than 3 m (9.8 ft) in length and the tubers are fairly small in most varieties.
The tubers are eaten baked, boiled, or fried much like potatoes. Because of the small size of the tubers, mechanical cultivation is possible, which along with its easy preparation and good flavor, could help the lesser yam to become more popular in the future.[12]
D. dumetorum[edit]
D. dumetorum, the bitter yam, is popular as a vegetable in parts of West Africa, in part because their cultivation requires less labor than other yams. The wild forms are very toxic and are sometimes used to poison animals when mixed with bait. It is said that they have also been used for criminal purposes.[12]
D. trifida[edit]
D. trifida, the cush-cush yam, is native to the Guyana region of South America and is the most important cultivated New World yam. Since they originated in tropical rainforest conditions, their growth cycle is less related to seasonal changes than other yams. Because of their relative ease of cultivation and their good flavor, they are considered to have a great potential for increased production.[12]
Harvesting[edit]
Yams in west Africa are typically harvested by hand using sticks, spades, or diggers.[16] Wood-based tools are preferred to metallic tools as they are less likely to damage the fragile tubers; however, wood tools need frequent replacement. Yam harvesting is labor-intensive and physically demanding. Tuber harvesting involves standing, bending, squatting, and sometimes sitting on the ground depending the size of mound, size of tuber, or depth of tuber penetration. Care must be taken to avoid damage to the tuber, because damaged tubers do not store well and spoil rapidly. Some farmers use staking and mixed cropping, a practice that complicates harvesting in some cases.
In forested areas, tubers grow in areas where other tree roots are present. Harvesting the tuber then involves the additional step of freeing them from other roots. This often causes tuber damage.
Aerial tubers or bulbils are harvested by manual plucking from the vine.
Yields may improve and cost of yam production be lower if mechanization were to be developed and adopted. However, current crop production practices and species used pose considerable hurdles to successful mechanization of yam production, particularly for small-scale rural farmers. Extensive changes in traditional cultivation practices, such as mixed cropping, may be required. Modification of current tuber harvesting equipment is necessary given yam tuber architecture and its different physical properties.[16]
Production[edit]
Further information: Yam production in Nigeria
Yam production - 2014
Country
Production
(millions of tonnes)
Nigeria 45.0
Ghana 7.1
Ivory Coast 5.8
Benin 3.2
Ethiopia 1.4
Togo 0.8
Cameroon 0.6
World 68.1
Source:UN Food & Agriculture Organization[17]
Worldwide yam production
In 2014, worldwide production of yams was 68.1 million tonnes, led by Nigeria with 66% of the global total (table). Nigeria farmed yams on 5.4 million hectares, 70% of the world land area of 7.8 million hectares devoted to yam farming.[17]
The world average annual yield of yams was 8.8 tonnes per hectare in 2014, with Ethiopia having the most productive farms of 29.7 tonnes per hectare.[17]
Storage[edit]
Roots and tubers such as yam are living organisms. When stored, they continue to respire, which results in the oxidation of the starch (a polymer of glucose) contained in the cells of the tuber, which converts it into water, carbon dioxide, and heat energy. During this transformation of the starch, the dry matter of the tuber is reduced.
Amongst the major roots and tubers, properly stored yam is considered to be the least perishable. Successful storage of yams requires:[18][19]
initial selection of sound and healthy yams
proper curing, if possible combined with fungicide treatment
adequate ventilation to remove the heat generated by respiration of the tubers
regular inspection during storage and removal of rotting tubers and any sprouts that develop
protection from direct sunlight and rain
Storing yam at low temperature reduces the respiration rates. However, temperatures below 12 °C (54 °F) cause damage through chilling, causing a breakdown of internal tissues, increasing water loss and yam's susceptibility to decay. The symptoms of chilling injury are not always obvious when the tubers are still in cold storage. The injury becomes noticeable as soon as the tubers are restored to ambient temperatures.
The best temperature to store yams is between 14 and 16 °C (57 and 61 °F), with high-technology-controlled humidity and climatic conditions, after a process of curing. Most countries that grow yam as food staple are too poor to afford high-technology storage systems.
Sprouting rapidly increases a tuber's respiration rates, and accelerates the rate at which its food value decreases.[18]
Certain cultivars of yams store better than others. The easier to store yams are those adapted to arid climate, where they tend to stay in a dormant low-respiration stage much longer than yam breeds adapted to humid tropical lands, where they do not need dormancy. Yellow yam and cush-cush yam, by nature, have much shorter dormancy periods than water yam, white yam, or lesser yam.
Storage losses for yams are very high in Africa, with insects alone causing over 25% harvest loss within 4 months.
Nutritional value[edit]
Yam, raw
Nutritional value per 100 g (3.5 oz)
Energy
494 kJ (118 kcal)
Carbohydrates
27.9 g
Sugars
0.5 g
Dietary fiber
4.1 g
Fat
0.17 g
Protein
1.5 g
Vitamins
Vitamin A equiv.
(1%)
7 μg
Thiamine (B1)
(10%)
0.112 mg
Riboflavin (B2)
(3%)
0.032 mg
Niacin (B3)
(4%)
0.552 mg
Pantothenic acid (B5)
(6%)
0.314 mg
Vitamin B6
(23%)
0.293 mg
Folate (B9)
(6%)
23 μg
Vitamin C
(21%)
17.1 mg
Vitamin E
(2%)
0.35 mg
Vitamin K
(2%)
2.3 μg
Minerals
Calcium
(2%)
17 mg
Iron
(4%)
0.54 mg
Magnesium
(6%)
21 mg
Manganese
(19%)
0.397 mg
Phosphorus
(8%)
55 mg
Potassium
(17%)
816 mg
Zinc
(3%)
0.24 mg
Link to USDA Database entry
Units
μg = micrograms • mg = milligrams
IU = International units
Percentages are roughly approximated using US recommendations for adults.
Source: USDA Nutrient Database
Raw yam has only moderate nutrient density, with appreciable content (10% or more of the Daily Value, DV) limited to potassium, vitamin B6, manganese, thiamin, dietary fiber, and vitamin C (table).[20] Yam supplies 118 Calories per 100 grams. Yam generally has a lower glycemic index, about 54% of glucose per 150-gram serving, compared to potato products.[21]
The protein content and quality of roots and tubers is lower than other food staples, with the content of yam and potato being around 2% on a fresh-weight basis. Yams, with cassava, provide a much greater proportion of the protein intake in Africa, ranging from 6% in East and South Africa to about 16% in humid West Africa.[citation needed]
As a relatively low-protein food, yam is not a good source of essential amino acids. Yam-consuming areas of Africa have a high incidence of kwashiorkor, a serious medical condition in children caused by protein deficiency. Experts emphasize the need to supplement a yam-dominant diet with more protein-rich foods to support healthy growth in children.[22][23]
Yam is an important dietary element for Nigerian and West African people. It contributes more than 200 calories per person per day for more than 150 million people in West Africa, and is an important source of income. Yam is an attractive crop in poor farms with limited resources. It is rich in starch, and can be prepared in many ways. It is available all year round, unlike other, unreliable, seasonal crops. These characteristics make yam a preferred food and a culturally important food security crop in some sub-Saharan African countries.[24]
Phytochemicals[edit]
The tubers of certain wild yam, a variant of kokoro yam and other species of Dioscorea, such as Dioscorea nipponica, are a source for the extraction of diosgenin, a steroid sapogenin.[25] The extracted diosgenin is used for the commercial synthesis of cortisone, pregnenolone, progesterone, and other steroid products.[26] Such preparations were used in early combined oral contraceptive pills.[27] The unmodified steroid has estrogenic activity.[28]
Comparison to other staple foods[edit]
The following table shows the nutrient content of yam and major staple foods in a raw harvested form. Raw forms, however, are not edible and cannot be digested. These must be sprouted, or prepared and cooked for human consumption. In sprouted or cooked form, the relative nutritional and antinutritional contents of each of these staples is remarkably different from that of raw form of these staples.[citation needed]
Nutrient content of major staple foods per 100 g portion[29]
Nutrient component:
Maize / Corn[A]
Rice (white)[B]
Rice (brown)[I]
Wheat[C]
Potato[D]
Cassava[E]
Soybean (Green)[F]
Sweet potato[G]
Yam[Y]
Sorghum[H]
Plantain[Z]
RDA
Water (g) 10 12 10 13 79 60 68 77 70 9 65 3000
Energy (kJ) 1528 1528 1549 1369 322 670 615 360 494 1419 511 8368–10,460
Protein (g) 9.4 7.1 7.9 12.6 2.0 1.4 13.0 1.6 1.5 11.3 1.3 50
Fat (g) 4.74 0.66 2.92 1.54 0.09 0.28 6.8 0.05 0.17 3.3 0.37
Carbohydrates (g) 74 80 77 71 17 38 11 20 28 75 32 130
Fiber (g) 7.3 1.3 3.5 12.2 2.2 1.8 4.2 3 4.1 6.3 2.3 30
Sugar (g) 0.64 0.12 0.85 0.41 0.78 1.7 0 4.18 0.5 0 15
Calcium (mg) 7 28 23 29 12 16 197 30 17 28 3 1000
Iron (mg) 2.71 0.8 1.47 3.19 0.78 0.27 3.55 0.61 0.54 4.4 0.6 8
Magnesium (mg) 127 25 143 126 23 21 65 25 21 0 37 400
Phosphorus (mg) 210 115 333 288 57 27 194 47 55 287 34 700
Potassium (mg) 287 115 223 363 421 271 620 337 816 350 499 4700
Sodium (mg) 35 5 7 2 6 14 15 55 9 6 4 1500
Zinc (mg) 2.21 1.09 2.02 2.65 0.29 0.34 0.99 0.3 0.24 0 0.14 11
Copper (mg) 0.31 0.22 0.43 0.11 0.10 0.13 0.15 0.18 - 0.08 0.9
Manganese (mg) 0.49 1.09 3.74 3.99 0.15 0.38 0.55 0.26 0.40 - - 2.3
Selenium (μg) 15.5 15.1 70.7 0.3 0.7 1.5 0.6 0.7 0 1.5 55
Vitamin C (mg) 0 0 0 0 19.7 20.6 29 2.4 17.1 0 18.4 90
Thiamin (B1)(mg) 0.39 0.07 0.40 0.30 0.08 0.09 0.44 0.08 0.11 0.24 0.05 1.2
Riboflavin (B2)(mg) 0.20 0.05 0.09 0.12 0.03 0.05 0.18 0.06 0.03 0.14 0.05 1.3
Niacin (B3) (mg) 3.63 1.6 5.09 5.46 1.05 0.85 1.65 0.56 0.55 2.93 0.69 16
Pantothenic acid (B5) (mg) 0.42 1.01 1.49 0.95 0.30 0.11 0.15 0.80 0.31 - 0.26 5
Vitamin B6 (mg) 0.62 0.16 0.51 0.3 0.30 0.09 0.07 0.21 0.29 - 0.30 1.3
Folate Total (B9) (μg) 19 8 20 38 16 27 165 11 23 0 22 400
Vitamin A (IU) 214 0 0 9 2 13 180 14187 138 0 1127 5000
Vitamin E, alpha-tocopherol (mg) 0.49 0.11 0.59 1.01 0.01 0.19 0 0.26 0.39 0 0.14 15
Vitamin K1 (μg) 0.3 0.1 1.9 1.9 1.9 1.9 0 1.8 2.6 0 0.7 120
Beta-carotene (μg) 97 0 5 1 8 0 8509 83 0 457 10,500
Lutein+zeaxanthin (μg) 1355 0 220 8 0 0 0 0 0 30
Saturated fatty acids (g) 0.67 0.18 0.58 0.26 0.03 0.07 0.79 0.02 0.04 0.46 0.14
Monounsaturated fatty acids (g) 1.25 0.21 1.05 0.2 0.00 0.08 1.28 0.00 0.01 0.99 0.03
Polyunsaturated fatty acids (g) 2.16 0.18 1.04 0.63 0.04 0.05 3.20 0.01 0.08 1.37 0.07
A yellow corn B raw unenriched long-grain white rice
C hard red winter wheat D raw potato with flesh and skin
E raw cassava F raw green soybeans
G raw sweet potato H raw sorghum
Y raw yam Z raw plantains
I raw long-grain brown rice
Consumption[edit]
Tongan farmer showing off his prize yams
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Yams are consumed in a variety of preparations, such as flour or whole vegetable pieces across their range of distribution in Asia, Africa, North America, Central America, the Caribbean, South America, and Oceania.[1]
Africa[edit]
Young women preparing fufu in the Democratic Republic of Congo
Yams of African species must be cooked to be safely eaten, because various natural substances in yams can cause illness if consumed raw. The most common cooking methods in Western and Central Africa are by boiling, frying or roasting.[30]
Among the Akan of Ghana, boiled yam can be mashed with palm oil into eto in a similar manner to the plantain dish matoke, and is served with eggs. The boiled yam can also be pounded with a traditional mortar and pestle to create a thick, starchy paste known as iyan (pounded yam) or fufu which is eaten with traditional sauces such as egusi and palm nut soup.
Another method of consumption is to leave the raw yam pieces to dry in the sun. When dry, the pieces turn a dark brown color. These are then milled to create a brown powder known in Nigeria as elubo. The powder can be mixed with boiling water to create a thick starchy paste, a kind of pudding known as amala, which is then eaten with local soups and sauces.
Yams are a primary agricultural and culturally important commodity in West Africa,[30] where over 95% of the world's yam crop is harvested. Yams are still important for survival in these regions. Some varieties of these tubers can be stored up to six months without refrigeration, which makes them a valuable resource for the yearly period of food scarcity at the beginning of the wet season. Yam cultivars are also cultivated in other humid tropical countries.[1]
Yam is the main staple crop of the Igbos in south eastern Nigeria where for centuries it played a dominant role in both their agricultural and cultural life. It is celebrated with annual yam festivals
Philippines and Costa Rica[edit]
Yams at Port-Vila market (Vanuatu)
A piece of cake made with ube (purple yam; Philippines)
In the Philippines, the purple ube species of yam (Dioscorea alata), is eaten as a sweetened dessert called ube halaya, and is also used as an ingredient in another Filipino dessert, halo-halo. It is also used as a popular ingredient for ice cream.
Vietnam[edit]
In Vietnam, the same purple yam is used for preparing a special type of soup canh khoai mỡ or fatty yam soup. This involves mashing the yam and cooking it until very well done.
Indonesia[edit]
In Indonesia, the same purple yam is used for preparing desserts. This involves mashing the yam and mixing it with coconut milk and sugar. White- and off-white-fleshed yams are cut in cubes, cooked, lightly fermented, and eaten as afternoon snacks.
Japan[edit]
Yamakake is a yam-based Japanese dish prepared from tororo and maguro.
An exception to the cooking rule is the mountain yam (Dioscorea polystachya), known as nagaimo and can be further classified into ichōimo (lit. 'ginkgo-leaf yam'; kanji: 銀杏芋), or yamatoimo (lit. Yamato yam; kanji: 大和芋), depending on the root shape.
Nagaimo is eaten raw and grated, after only a relatively minimal preparation: the whole tubers are briefly soaked in a vinegar-water solution to neutralize irritant oxalate crystals found in their skin. The raw vegetable is starchy and bland, mucilaginous when grated, and may be eaten plain as a side dish, or added to noodles.
Another variety of yam, jinenjo, is used in Japan as an ingredient in soba noodles. In Okinawa, purple yams (Dioscorea alata) are grown. This is known locally as daijo or beniimo. This purple yam is popular as lightly deep-fried tempura, as well as being grilled or boiled. Additionally, the purple yam is a common ingredient of yam ice cream with the signature purple color. Purple yam is also used in other types of traditional wagashi sweets, cakes, and candy.
India[edit]
In central parts of India, the yam (khamalu, suran, or chupri alu) is prepared by being finely sliced, seasoned with spices, and deep fried. In southern parts of India, known as karunai kizhangu in Tamil, the vegetable is a popular accompaniment to rice dishes and fish curry. Also eaten in India, D. alata, a purple-pigmented species, is known as ratalu or violet yam.
In the southern part, especially in Kerala, both purple and white colored yams are locally known as kaachil or kavuttu.
In Karnataka, it is known as suvarna gadde in Kannada language. In central India, it is also called g.aradu In Andhra Pradesh, it is known as ganisi gadda.
Nepal[edit]
Dioscorea root is traditionally eaten on Māgh Sankrānti (a midwinter festival) in Nepal. In Nepali, it is called tarul and in Newari hī. It is usually steamed and then cooked with spices.
Fiji Islands[edit]
Yam, known locally in Fiji as "uvi",[31] may replace cassava or taro as a staple, and is consumed boiled, roasted in a lovo, or steamed with fish or meat in curry sauce or coconut milk and served with rice. The cost of yam is higher due to the difficulty in farming and relatively low volume of production on Fiji.[31]
The West[edit]
Yam powder is available in the West from grocers specializing in African products, and may be used in a similar manner to instant mashed potato powder, although preparation is a little more difficult because of the tendency to form lumps. The yam powder is sprinkled onto a pan containing a small amount of boiling water, and stirred vigorously. The resulting mixture is served with a heated sauce, such as tomato and chili, poured onto it.
Because of their abundance and importance to survival, yams were highly regarded in Jamaican ceremonies and constitute part of many traditional West African ceremonies.[32]
Toxicity[edit]
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Unlike cassava, most varieties of edible, mature, cultivated yam do not contain toxic compounds. However, there are exceptions. Bitter compounds tend to accumulate in immature tuber tissues of white and yellow yams. These may be polyphenols or tannin-like compounds.[citation needed]
Wild forms of bitter yams do contain some toxins that taste bitter, hence are referred to as bitter yam. Bitter yams are not normally eaten except at times of desperation in poor countries and in times of local food scarcity. They are usually detoxified by soaking in a vessel of salt water, in cold or hot fresh water or in a stream. The bitter compounds in these yams are water-soluble alkaloids which, on ingestion, produce severe and distressing symptoms. Severe cases of alkaloid intoxication may prove fatal.
Aerial or potato yams have antinutritional factors. In Asia, detoxification methods, involving water extraction, fermentation, and roasting of the grated tuber, are used for bitter cultivars of this yam. The bitter compounds in yams also known locally as air potato include diosbulbin and possibly saponins, such as diosgenin.[25] In Indonesia, an extract of air potato is used in the preparation of arrow poison.[18]
Ashanti yam ceremony in Ghana has been part of the local history, shown in this 1817 painting of a yam ceremony
Cultural aspects[edit]
Nigeria and Ghana[edit]
A yam festival is usually held in the beginning of August at the end of the rainy season. People offer yams to gods and ancestors first, before distributing them to the villagers. This is their way of giving thanks to the spirits above them.
New Yam Festival[edit]
The New Yam Festival celebrates the main agricultural crop of the Igbos, Idomas, and Tivs. The New Yam Festival, known as Orureshi in Owukpa in Idoma west and Ima-Ji, Iri-Ji or Iwa Ji in Igbo land, is a celebration depicting the prominence of yam in social and cultural life. The festival is prominent among southeastern states and major tribes in Benue State, mainly around August.
Other[edit]
Historical records in West Africa and of African yams in Europe date back to the 16th century. Yams were taken to the Americas through precolonial Portuguese and Spanish on the borders of Brazil and Guyana, followed by a dispersion through the Caribbean.[33]
Yams are used in Papua New Guinea, where they are called kaukau. Their cultivation and harvesting is accompanied by complex rituals and taboos. The coming of the yams (one of the numerous versions from Maré) is described in Pene Nengone (Loyalty Islands – New Caledonia).
References[edit]
^ Jump up to: a b c d e f g h i j k l m n o p q r s "Dioscorea alata (white yam)". Centre for Agriculture and Biosciences International (CABI). 2017. Retrieved 5 December 2017.
^ Jump up to: a b "Yam". Online Etymology Dictionary, Douglas Harper. 2017. Retrieved 5 December 2017.
Jump up ^ LOC.gov, What is the difference between sweet potatoes and yams?
Jump up ^ USDA.gov
Jump up ^ "...but in New Zealand we call them yams.", garden-nz.co.nz
Jump up ^ Albihn, P.B.E.; Savage, G.P. (June 18, 2001). "The effect of cooking on the location and concentration of oxalate in three cultivars of New Zealand-grown oca (Oxalis tuberosa Mol)". Journal of the Science of Food and Agriculture. 81 (10): 1027–1033. doi:10.1002/jsfa.890.
Jump up ^ "FDA bans more konjac products"
Jump up ^ "I yam not taro" Dr Lim Chin Lam, The Star
Jump up ^ "Everyday Mysteries: Yam". Library of Congress, United States of America. 2011.
^ Jump up to: a b Calverly (1998). "Storage and Processing of Roots and Tubers in the Tropics". Food and Agriculture Association of the United Nations.
Jump up ^ Dumont, R.; Vernier, P. (2000). "Domestication of yams (Dioscorea cayenensis-rotundata) within the Bariba ethnic group in Benin". Outlook on Agriculture. 29 (2): 137. doi:10.5367/000000000101293149.
^ Jump up to: a b c d e f Kay, D.E. (1987). Root Crops. Tropical Development and Research Institute : London
Jump up ^ Mignouna, H.D., Abang, M.M., & Asiedu, R. (2003). Harnessing Modern Biotechnology for Tropical Tuber Crop Improvement: Yam (Dioscorea spp.) Molecular Breeding. Available online.
Jump up ^ * White, L.D. (2003). Canoe Plants of Ancient Hawai'i: Uhi
Jump up ^ Schultz, G.E. (1993). Element Stewardship Abstract for Dioscorea bulbifera, Air potato. Nature Conservancy
^ Jump up to: a b Linus Opara (2003). "YAMS: Post-Harvest Operation" (PDF).
^ Jump up to: a b c "Yam production in 2014; Crops/Regions/World/Production Quantity; from pick lists". FAOSTAT, Statistics Division of the UN Food and Agriculture Organization. 2017. Retrieved 31 May 2017.
^ Jump up to: a b c Oke (1990). "Roots, tubers, plantains and bananas in human nutrition". FAO. ISBN 92-5-102862-1.
Jump up ^ "Roots, Tubers, and Plantains in Food Security: In Sub-Saharan Africa, in Latin America and the Caribbean, in the Pacific". FAO. 1989. ISBN 978-92-5-102782-0. Missing or empty |url= (help)
Jump up ^ Uwaegbute, Osho and Obatolu (1998). Postharvest technology and commodity marketing: Proceedings of a postharvest conference. International Institute of Tropical Agriculture. p. 172. ISBN 978-978-131-111-6.
Jump up ^ "Glycemic index and glycemic load for 100+ foods". Harvard Health Publications, Harvard Medical School. 2008.
Jump up ^ "Kwashiorkor (Protein-Calorie Malnutrition)". Tropical Medicine Central Resource. 2006.
Jump up ^ "Undernutrition". The Merck Manual: The Home Health Handbook. 2010.
Jump up ^ Izekor and Olumese (December 2010). "Determinants of yam production and profitability in Edo State, Nigeria" (PDF). African Journal of General Agriculture. 6 (4).
^ Jump up to: a b Jesus, M; Martins, A. P; Gallardo, E; Silvestre, S (2016). "Diosgenin: Recent Highlights on Pharmacology and Analytical Methodology". Journal of Analytical Methods in Chemistry. 2016: 4156293. doi:10.1155/2016/4156293. PMC 5225340  . PMID 28116217.
Jump up ^ Marker RE, Krueger J (1940). "Sterols. CXII. Sapogenins. XLI. The Preparation of Trillin and its Conversion to Progesterone". J. Am. Chem. Soc. 62 (12): 3349–3350. doi:10.1021/ja01869a023.
Jump up ^ Djerassi C (December 1992). "Steroid research at Syntex: "the pill" and cortisone". Steroids. 57 (12): 631–41. doi:10.1016/0039-128X(92)90016-3. PMID 1481227.
Jump up ^ Liu MJ, Wang Z, Ju Y, Wong RN, Wu QY (2005). "Diosgenin induces cell cycle arrest and apoptosis in human leukemia K562 cells with the disruption of Ca2+ homeostasis". Cancer Chemother. Pharmacol. 55 (1): 79–90. doi:10.1007/s00280-004-0849-3. PMID 15372201.
Jump up ^ "Nutrient data laboratory". United States Department of Agriculture. Retrieved August 10, 2016.
^ Jump up to: a b Felix Nweke; Robert Aidoo; Benjamin Okoye (July 2013). "Yam Consumption Patterns in West Africa". Bill and Melinda Gates Foundation. Retrieved 5 December 2017.
^ Jump up to: a b Naleba, Mere (25 April 2015). "Million dollar aim". The Fiji Times Online. Retrieved 1 June 2017.
Jump up ^ Jack Goody (1996). Cooking, Cuisine and Class: A Study in Comparative Sociology. pp. 78–81. ISBN 978-0-521-28696-1.
Jump up ^ "Roots, tubers, plantains and bananas in human nutrition – Acknowledgments, Preface, Introduction, Origins and distribution". fao.org.
External links[edit]
IITA: Yam crop improvement
Wikisource has the text of the 1905 New International Encyclopedia article Yam.
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value: يام (نبات) – Arabic

value:
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Ku – Bambara
bm
bm
interlanguage-link-target

value:
https://bi.wikipedia.org/wiki/Yam
Yam – Bislama
bi
bi
interlanguage-link-target

value: ཞོག་རྒོད། – Tibetan

value:
https://bs.wikipedia.org/wiki/Jam
Jam – Bosnian
bs
bs
interlanguage-link-target

value:
https://ca.wikipedia.org/wiki/Nyam
Nyam – Catalan
ca
ca
interlanguage-link-target

value:
https://da.wikipedia.org/wiki/Yams
Yams – Danish
da
da
interlanguage-link-target

value: Γιαμ – Greek

value:
https://es.wikipedia.org/wiki/%C3%91ame
Ñame – Spanish
es
es
interlanguage-link-target

value:
https://eo.wikipedia.org/wiki/Ignamo
Ignamo – Esperanto
eo
eo
interlanguage-link-target

value:
https://eu.wikipedia.org/wiki/%C3%91ame
Ñame – Basque
eu
eu
interlanguage-link-target

value: یم (سبزیجات) – Persian

value:
https://fr.wikipedia.org/wiki/Igname
Igname – French
fr
fr
interlanguage-link-target

value:
https://ff.wikipedia.org/wiki/Kappe
Kappe – Fulah
ff
ff
interlanguage-link-target

value:
https://ga.wikipedia.org/wiki/Ionam
Ionam – Irish
ga
ga
interlanguage-link-target

value:
https://ha.wikipedia.org/wiki/Doya
Doya – Hausa
ha
ha
interlanguage-link-target

value:
https://hr.wikipedia.org/wiki/Jam
Jam – Croatian
hr
hr
interlanguage-link-target

value:
https://io.wikipedia.org/wiki/Inyamo
Inyamo – Ido
io
io
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value:
https://ig.wikipedia.org/wiki/J%C3%AD
Jí – Igbo
ig
ig
interlanguage-link-target

value:
https://ht.wikipedia.org/wiki/Yanm
Yanm – Haitian Creole
ht
ht
interlanguage-link-target

value:
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Jamsz – Hungarian
hu
hu
interlanguage-link-target

value:
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Uvi – Fijian
fj
fj
interlanguage-link-target

value:
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Yam – Dutch
nl
nl
interlanguage-link-target

value:
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Yam – Norwegian
no
no
interlanguage-link-target

value:
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Jams – Norwegian Nynorsk
nn
nn
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value:
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Nham – Occitan
oc
oc
interlanguage-link-target

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Yams – Uzbek
uz
uz
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Inhame – Portuguese
pt
pt
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Yam – Simple English
simple
simple
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Jamssit – Finnish
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Jams – Swedish
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sv
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Khoai – Vietnamese
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Isu – Yoruba
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