Sweet potato

The sweet potato (Ipomoea batatas) is a dicotyledonous plant that belongs to the family Convolvulaceae. Its large, starchy, sweet tasting tuberous roots are an important root vegetable (Purseglove, 1991; Woolfe, 1992). The young leaves and shoots are sometimes eaten as greens. Of the approximately 50 genera and more than 1,000 species of Convolvulaceae, I. batatas is the only crop plant of major importance – some others are used locally, but many are actually poisonous.

The sweet potato is only distantly related to the potato (Solanum tuberosum). The softer, orange variety is commonly marketed as a "yam" in parts of North America, a practice intended to differentiate it from the firmer, white variety. The sweet potato is botanically very distinct from the actual yam, which is native to Africa and Asia and belongs to the monocot family Dioscoreaceae. To prevent confusion, the United States Department of Agriculture requires that sweet potatoes labeled as "yams" also be labeled as "sweet potatoes".^[1]

The genus Ipomoea that contains the sweet potato also includes several garden flowers called morning glories, though that term is not usually extended to Ipomoea batatas. Some cultivars of Ipomoea batatas are grown as ornamental plants; the name "tuberous morning glory" may be used in a horticultural context.

This plant is a herbaceous perennial vine, bearing alternate heart-shaped or palmately lobed leaves and medium-sized sympetalous flowers. The edible tuberous root is long and tapered, with a smooth skin whose colour ranges between red, purple, brown and white. Its flesh ranges from white through yellow, orange, and purple.

Contents 1 Origin, distribution and diversity 2 Cultivation 2.1 Diseases 3 Nutrition and health benefits 3.1 Culinary uses 3.1.1 Africa 3.1.2 Asia 3.1.3 North America 3.1.4 Other 3.2 Non-culinary uses 4 Names 4.1 Spain and Latin America 5 References 6 Further reading 7 External links

Origin, distribution and diversity

Sweet potatoes are native to the tropical parts of South America, and were domesticated there at least 5000 years ago.^[2]

Austin (1988) postulated that the centre of origin of I. batatas was between the Yucatán Peninsula of Mexico and the mouth of the Orinoco River in Venezuela. The 'cultigen' had most likely been spread by local people to the Caribbean and South America by 2500 BC. Zhang et al. (1998) provided strong supporting evidence that the geographical zone postulated by Austin is the primary centre of diversity. The much lower molecular diversity found in Peru–Ecuador suggests that this region be considered as secondary centre of sweet potato diversity.

The sweet potato was also grown before western exploration in Polynesia, where it is known as the kumara, remarkably similar to the Quechua kumar in Peru. Sweet potato has been radiocarbon-dated in the Cook Islands to 1000 AD, and current thinking is that it was brought to central Polynesia circa 700 AD, possibly by Polynesians who had traveled to South America and back, and spread across Polynesia to Hawaii and New Zealand from there.^[3] It is possible however, that South Americans brought it to the Pacific. The theory that the plant could spread by floating seeds across the ocean is not supported by evidence. Another point is that the sweet potato in Polynesia is the cultivated Ipomoea batatas, which is generally spread by vine cuttings, and not by seeds.^[4]

Sweet potatoes are now cultivated throughout tropical and warm temperate regions wherever there is sufficient water to support their growth.

According to the Food and Agriculture Organization (FAO) statistics, world production in 2004 was 127,000,000 tonnes.^[5] The majority comes from China, with a production of 105,000,000 tonnes from 49,000 km². About half of the Chinese crop is used for livestock feed.^[2]

Per-capita production is greatest in countries where sweet potatoes are a staple of human consumption, led by Papua New Guinea at 550 kg^[6] per person per year, the Solomon Islands at 160 kg, Burundi and Rwanda^[7] at 130 kg and Uganda at 100 kg.

About 20,000 tonnes of sweet potatoes are produced annually in New Zealand, where sweet potato is known by its Māori name, kūmara. It was a staple food for Māori before European contact.^[8]

In the U.S., North Carolina, the leading state in sweet potato production, provided 38.5% of the 2007 U.S. production of sweet potatoes. California, Louisiana, and Mississippi compete closely with each other in production. Louisiana has been a long-time major producer, once second only to North Carolina, and closely followed by California, until the latter began surpassing it in 2002. In 2007, California produced 23%, Louisiana 15.9%, and Mississippi 19% of the U.S. total.^[9][10]

The town of Opelousas, Louisiana's "Yambilee" has been celebrated every October since 1946. The Frenchmen who established the first settlement at Opelousas in 1760 discovered the native Attakapas, Alabama, Choctaw, and Opelousas tribes eating sweet potatoes. The sweet potato became a favourite food item of the French and Spanish settlers, and thus continued a long history of cultivation in Louisiana.^[11]

Mississippi has about 150 farmers presently growing sweet potatoes on about 8,200 acres (33 km²), contributing $19 million dollars to the state's economy. Mississippi's top five sweet potato producing counties are Calhoun, Chickasaw, Pontotoc, Yalobusha, and Panola. The National Sweet Potato Festival is held annually the entire first week in November in Vardaman (Calhoun County), which proclaims itself as "The Sweet Potato Capital".

The town of Benton, Kentucky celebrates the sweet potato annually with its Tater Day Festival on the first Monday of April. The town of Gleason, Tennessee celebrates the sweet potato on Labor Day weekend with its Tater Town Special.

Cultivation

The plant does not tolerate frost. It grows best at an average temperature of 24 °C (75 °F), abundant sunshine and warm nights. Annual rainfalls of 750–1000 mm are considered most suitable, with a minimum of 500 mm in the growing season. The crop is sensitive to drought at the tuber initiation stage 50–60 days after planting and is not tolerant to water-logging, as it may cause tuber rots and reduce growth of storage roots if aeration is poor (Ahn, 1993).

Depending on the cultivar and conditions, tuberous roots mature in two to nine months. With care, early-maturing cultivars can be grown as an annual summer crop in temperate areas, such as the northern United States. Sweet potatoes rarely flower when the daylight is longer than 11 hours, as is normal outside of the tropics. They are mostly propagated by stem or root cuttings or by adventitious roots called "slips" that grow out from the tuberous roots during storage. True seeds are used for breeding only.

Under optimal conditions of 85 to 90% relative humidity at 13 to 16 °C (55 to 61 °F), sweet potatoes can keep for six months. Colder temperatures injure the roots.

They grow well in many farming conditions and have few natural enemies; pesticides are rarely needed. Sweet potatoes are grown on a variety of soils, but well-drained light and medium textured soils with a pH range of 4.5-7.0 are more favourable for the plant (Woolfe, 1992; Ahn, 1993). They can be grown in poor soils with little fertilizer. However, sweet potatoes are very sensitive to aluminium toxicity and will die about 6 weeks after planting if lime is not applied at planting in this type of soil (Woolfe, 1992). Because they are sown by vine cuttings rather than seeds, sweet potatoes are relatively easy to plant. Because the rapidly growing vines shade out weeds, little weeding is needed, and farmers can devote time to other crops. In the tropics, the crop can be maintained in the ground and harvested as needed for market or home consumption. In temperate regions, sweet potatoes are most often grown on larger farms and are harvested before first frosts.

China is the largest grower of sweet potatoes, providing about 80% of the world's supply; 130 million tons were produced in one year (in 1990; about half that of common potatoes). Historically, most of China's sweet potatoes were grown for human consumption, but now most (60%) are grown to feed pigs. The rest are grown for human food and for other products. Some are grown for export, mainly to Japan. China grows over 100 varieties of sweet potato.

Sweet potatoes very early became popular in the islands of the Pacific Ocean, spreading from Polynesia to Japan and the Philippines. One reason is that they were a reliable crop in cases of crop failure of other staple foods due to typhoon flooding. They are featured in many favorite dishes in Japan, Taiwan, the Philippines, and other island nations. Indonesia, Vietnam, India, and some other Asian countries are also large sweet potato growers. Uganda (the third largest grower after Indonesia), Rwanda, and some other African countries also grow a large crop which is an important part of their peoples' diets. North and South America, the original home of the sweet potato, together grow less than three percent of the world's supply. Europe has only a very small sweet potato production, mostly in Portugal. In the Caribbean, a variety of the sweet potato called the boniato is very popular. The flesh of the boniato is cream-coloured, unlike the more popular orange hue seen in other varieties. Boniatos are not as sweet and moist as other sweet potatoes, but many people prefer their fluffier consistency and more delicate flavor. Boniatos have been grown throughout the subtropical world for centuries, but became an important commercial crop in Florida in recent years.

Sweet potatoes have been an important part of the diet in the United States for most of its history, especially in the Southeast. From the middle of the 20th century, however, they have become less popular. The average per capita consumption of sweet potatoes in the United States is only about 1.5–2 kg (3.3–4.4 lb) per year, down from 13 kg (29 lb) in 1920. Southerner Kent Wrench writes: "The Sweet Potato became associated with hard times in the minds of our ancestors and when they became affluent enough to change their menu, the potato was served less often."^[12]

New Zealanders grow enough kūmara to provide each person with 7 kg (15 lb) per year, and also import substantially more than this from China.

Diseases

Nutrition and health benefits

Raw Sweet Potato

Nutritional value per 100 g (3.5 oz)
Energy	360 kJ (86 kcal)
Carbohydrates	20.1 g
Starch	12.7 g
Sugars	4.2 g
Dietary fibre	3.0 g
Fat	0.1 g
Protein	1.6 g
Vitamin A equiv.	709 μg (79%)
- beta-carotene	8509 μg (79%)
- lutein and zeaxanthin	0 μg
Thiamine (Vit. B1)	0.1 mg (8%)
Riboflavin (Vit. B2)	0.1 mg (7%)
Niacin (Vit. B3)	0.61 mg (4%)
Pantothenic acid (B5)	0.8 mg (16%)
Vitamin B6	0.2 mg (15%)
Folate (Vit. B9)	11 μg (3%)
Vitamin C	2.4 mg (4%)
Calcium	30.0 mg (3%)
Iron	0.6 mg (5%)
Magnesium	25.0 mg (7%)
Phosphorus	47.0 mg (7%)
Potassium	337 mg (7%)
Sodium	55 mg (2%)
Zinc	0.3 mg (3%)
Percentages are relative to US recommendations for adults. Source: nutritiondata.comSource: USDA Nutrient database

Besides simple starches, sweet potatoes are rich in complex carbohydrates, dietary fiber, beta carotene (a vitamin A equivalent nutrient), vitamin C, and vitamin B₆. Pink and yellow varieties are high in carotene, the precursor of vitamin A.

In 1992, the Center for Science in the Public Interest compared the nutritional value of sweet potatoes to other vegetables. Considering fibre content, complex carbohydrates, protein, vitamins A and C, iron, and calcium, the sweet potato ranked highest in nutritional value. According to these criteria, sweet potatoes earned 184 points, 100 points over the next on the list, the common potato.(NCSPC)

Sweet potato varieties with dark orange flesh have more beta carotene than those with light coloured flesh, and their increased cultivation is being encouraged in Africa, where vitamin A deficiency is a serious health problem. Despite the name "sweet", it may be a beneficial food for diabetics, as preliminary studies on animals have revealed that it helps to stabilize blood sugar levels and to lower insulin resistance.^[13]

The peptic substance (0.78 percent total, 0.43 percent soluble) present in fresh tubers contains uronic acid (60 percent) and methoxyl (4 to 5 percent). Other constituents include phytin (1.05 percent), two monoaminophosphatides (probably lecithin and cephalin), organic acids (oxalic acid), phytosterolin, phytosterol, resins, tannins, and colouring matter. (Hug et al., 1983).

Culinary uses

Although the leaves and shoots are also edible, the starchy tuberous roots are by far the most important product. In some tropical areas, they are a staple food-crop.

Africa

• "Amukeke" (sun dried slices of storage roots) and "inginyo" (sun dried crushed storage roots) are a staple food for people in northeastern Uganda (Abidin, 2004). Amukeke is mainly for breakfast, eaten with peanut sauce. People generally eat this food while they are drinking a cup of tea in the morning, around 10 am. Inginyo will be mixed with cassava flour and tamarind, to make food called "atapa". People eat "atapa" with smoked fish cooked in peanut sauce or with dried cowpea leaves cooked in peanut sauce.
• The young leaves and vine tips of sweet potato leaves are widely consumed as a vegetable in West African countries (Guinea, Sierra Leone and Liberia, for example), as well as in northeastern Uganda, East Africa (Abidin, 2004). According to FAO leaflet No. 13 - 1990, sweet potato leaves and shoots are a good source of vitamins A, C, and B₂ (Riboflavin), and according to research done by A. Khachatryan, are an excellent source of lutein.
• Steamed/boiled chunks are boiled in water or cooked by microwave.

Asia

• In China, sweet potatoes, typically of the yellow variety, are often baked in a large iron drum and sold as street food during winter.^[14]. In Japan, this is called Yaki-imo (roasted sweeted potato) and typically use the purple colored yam, which is not a sweet potato
• Sweet potato soup a type of Chinese tong sui (sweet soup) that is served during winter consists of boiling sweet potato in water with rock sugar and ginger.
• Sweet potato greens are a common side dish in Taiwanese cuisine, often boiled or sautéed and served with a garlic and soy sauce mixture, or simply salted before serving. They, as well as dishes featuring the sweet potato root, are commonly found at bento (POJ: piān-tong) restaurants, .
• In northeastern Chinese cuisine, sweet potatoes are often cut into chunks and fried, before being drenched into a pan of boiling syrup.^[15]
• In Korean cuisine, sweet potato starch is used to produce dangmyeon (cellophane noodles). Sweet potatoes are also boiled, steamed, or roasted, and young stems are eaten as namul. Pizza Restaurants such as Pizza Hut and Dominoes in Korea are using sweet potatoes as a popular topping.
• In Japan, boiled sweet potato is the most common way to eat it at home. Also, the use in vegetable tempura is common.
  • Daigaku-imo is a baked sweet potato dessert.
  • Because it is sweet and starchy, it is used in imo-kinton and some other wagashi (Japanese sweets), such as ofukuimo.
  • Shōchū, a Japanese spirit normally made from the fermentation of rice, can also be made from sweet potato, in which case it is called imo-jōchū.
• Imo-gohan, sweet potato cooked with rice, is popular in both Japan and Taiwan. It is also served in nimono or nitsuke, boiled and typically flavoured with soy sauce, mirin and dashi.
• In Malaysia, sweet potato is often cut into small cubes and cooked with yam and coconut milk (santan) to make a sweet dessert called bubur caca. A favourite way of cooking sweet potato is deep frying slices of sweet potato in batter, and served as a tea-time snack. In houses, sweet potatoes are usually boiled. The leaves of sweet potatoes are usually stir-fried with only garlic or with sambal belacan and dried shrimp by the Malaysian Chinese.
• In India, in some regions fasts of religious nature are an occasion for a change in normal diet, and a total absence from cooking or eating is held as elective while a normal diet for a fasting day is a light feast consisting of different foods from usual, amongst which sweet potato is one of the prime sources of sustainance. Sweet potato is eaten otherwise too, and a popular variety of preparation in most parts is roasted slow over kitchen coals at night and eaten with some dressing - primarily salt, possibly yogurt - while the easier way in south is simply boiling or pressure cooking before peeling, cubing and seasoning for a vegetable dish as part of the meal. Usually the preparations for sweet potato are similar to the blander ones for potato, while the sharper versions - with more green chilly or red pepper - are reserved for potato.
• In the Philippines- called "Camote" -it is an important crop and food for many poor inhabitants in the provinces. The leaves and shoots are eaten with salted shrimp paste "bagoong alamang" or fish sauce or salted fish for viand. The tubers are cooked as boiled, or put under the coals. Most street vendors in the metropolis cooked it with sugary syrup and called "camote cue".

North America

• Candied sweet potatoes are a side dish consisting mainly of sweet potatoes prepared with brown sugar, marshmallows, maple syrup, molasses, orange juice, marron glacé, or other sweet ingredients. Often served in America on Thanksgiving, this dish represents traditional American cooking and of that prepared with the indigenous peoples of the Americas when European American settlers first arrived.
• Sweet potato pie is also a traditional favourite dish in southern U.S. cuisine.
• Sweet potatoes slices are fried in bacon drippings and eaten with the bacon on toast. This is a traditional autumn breakfast food in rural Kentucky.
• Sweet potato fries or chips are another common preparation, and are made by julienning and deep frying sweet potatoes, in the fashion of French fried potatoes.
• Baked sweet potatoes are sometimes offered in restaurants as an alternative to baked potatoes. They are often topped with brown sugar and butter.
• In Dominican Republic, sweet potato is enjoyed for breakfast.
• Sweet potato butter can be cooked into a gourmet spread.

Other

• In New Zealand, Māori traditionally cooked their kūmara in hāngi (earth ovens). Rocks were placed on a fire in a large hole. When the fire died out, kūmara and other food was wrapped in leaves and placed on the hot rocks, then covered with earth. The kūmara was dug up again several hours later. The resulting food was very soft and tender, as though steamed. However, hangi are rare in modern New Zealand, and New Zealanders, Maori or Pakeha are more likely to consume it baked, boiled, or deep-fried (such as in kumara chips) than they are in hāngi.
• In the Solomon Islands, and neighbouring Melanesian countries (as well as some parts of Polynesia), the sweet potato, along with the yam, also goes by the name common desert truffle.^[16]
• In Catalonia (northeastern Spain), sweet potato is called "boniato." On the evening of All Souls' Day, it's traditional to serve roasted sweet potato and chestnuts, panellets, and sweet wine. The occasion is called La Castanyada ^[17].

Non-culinary uses

In South America, the juice of red sweet potatoes is combined with lime juice to make a dye for cloth. By varying the proportions of the juices, every shade from pink to purple to black can be obtained. (Verrill p. 47)

All parts of the plant are used for animal fodder.

Sweet potatoes or camotes are often found in Moche ceramics.^[18]

Several selections are cultivated in gardens as ornamental plants for their attractive foliage, including the dark-leafed cultivars 'Blackie' and 'Ace of Spades' and the chartreuse-foliaged 'Margarita'. The species called wild sweet potato vine, man root, or man-of-the-earth is not edible, but it is cultivated as an ornamental vine.

Taiwanese companies are making alcohol fuel from sweet potato.

Names

Although it is sometimes called a yam, the sweet potato is not in the yam family, nor is it closely related to the common potato. The first Europeans to taste sweet potatoes were members of Columbus' expedition in 1492. Later explorers found many varieties under an assortment of local names, but the name which stayed was the indigenous Taino name of batata. This name was later transmuted to the similar name for a different vegetable—the ordinary potato, causing confusion from which it never recovered. The first record of the name "sweet potato" is found in the Oxford English Dictionary of 1775.

In the Tok Pisin language of Papua New Guinea the edible tubers are known as kaukau.^[19]

Spain and Latin America

The Spanish took the Taino name batata directly, and also combined it with the Quechua word for potato, papa, to create the word patata for the common potato. In Mexico and Central America, the sweet potato is called by the Nahuatl-derived name camote. In Peru, the Quechua name for a type of sweet potato is kumar, strikingly similar to the Polynesian name kumara (see below).

In South America, Peruvian sweet potato remnants dating as far back as 8,000 BC have been found.^[20]

For other languages' native words for sweet potato, see the Wiktionary entry for "sweet potato"

References

Further reading

• Abidin, P.E. 2004. Sweetpotato breeding for northeastern Uganda: Farmer varieties, farmer-participatory selection, and stability of performance. PhD Thesis, Wageningen University, The Netherlands, 152 pp. ISBN 90-8504-033-7.
• Ahn, P.M., 1993, "Tropical soils and fertilizer use", Intermediate Trop. Agric. Series. Longman Sci. and Tech. Ltd. UK.
• Austin, D.F. 1988. The taxonomy, evolution and genetic diversity of sweetpotatoes and related wild species. In: P. Gregory (ed.). Exploration, maintenance, and utilization of sweetpotato genetic resources, pp. 27–60. CIP, Lima, Peru.
• Hartemink, A.E., S. Poloma, M. Maino, K.S. Powell, J. Egenae & J. N. Sullivan, (2000). Yield decline of sweet potato in the humid lowlands of Papua New Guinea. Agriculture, Ecosystems and Environment 79 (2-3), 259-269.
• Verrill, A.H., Foods America Gave the World, 1937, Boston: L.C. Page & Co.
• Woolfe, J.A., 1992, "Sweetpotato: an untapped food resource", Cambridge Univ. Press and the International Potato Center (CIP). Cambridge, UK.
• Zhang, D.P., M. Ghislain, Z. Huamán, J.C. Cervantes and E.E. Carey 1998. AFLP assessment of sweetpotato genetic diversity in four tropical American regions. CIP Program Report 1997-1998, pp. 303–310.

External links

• Batatas, not potatoes
• The mystery of the sweet potato
• Consultative Group on International Agricultural Research (CGIAR), "Sweet Potato"
• Food and Agricultural Organization of the United Nations (FAO), 1990, "Roots, tubers, plantains and bananas in human nutrition"
• FAO Leaflet No. 13 - 1990 - Sweet Potato
• Purseglove, J.W. 1991. Tropical crops. Dicotyledons. Longman Scientific and Technical. John Wiley and Sons, Inc. NY. USA.
• The Japanese Society of Root and Tuber Crops (JRT), "Mini White Paper: Sweetpotato in Japan" 2000
• Wrench, K., "The Sweet Potato Patch"
• Sweetpotato DiagNotes is a free comprehensive tool for sweetpotato management, providing information across the disciplines of plant pathology, crop nutrition, entomology and pest management, all integrated in a single expert system.
• Identification of sweet potato leaves (Ipomoea batatas) as an excellent source of lutein. A. KHACHATRYAN
• World's Healthiest Foods: Benefits of Sweet Potatoes
• Can camote tops cure dengue? - 01/25/2008