Potato
2008/9 Schools Wikipedia Selection. Related subjects: Food; Plants
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| Solanum tuberosum L. |
Potato is the term which applies either to the starchy tuberous crop from the perennial plant Solanum tuberosum of the Solanaceae, or nightshade, family, or to the plant itself. Potato is the world's most widely grown tuber crop, and the fourth largest food crop in terms of fresh produce — after rice, wheat, and maize (corn).
The potato originated in the area of contemporary Peru and Bolivia, identified more specifically in research published by David Spooner in 2005 as an area of southern Peru, just north of Lake Titicaca. The potato was introduced to Europe around 1700, and subsequently by European mariners to territories and ports throughout the world. Thousands of varieties persist in the Andes, where over 100 varieties might be found in a single valley, and a dozen or more might be maintained by a single agricultural household.
Once established in Europe, potato soon became an important food staple and field crop. Lack of genetic diversity, due to the fact that very few varieties were initially introduced, left the crop vulnerable to disease. In 1845, a fungal disease, Phytophthora infestans, also known as late blight, spread rapidly through the poorer communities of western Ireland, resulting in the Great Irish Famine. The potato is also strongly associated with Idaho, Maine, North Dakota, Prince Edward Island, Ireland, Jersey and Russia because of its large role in the agricultural economy and history of these regions. But in recent decades, the greatest expansion of potato has been in Asia, where as of 2007 approximately eighty percent of the world potato crop is grown. Since the dissolution of the Soviet Union, China has become the world's largest potato producer, followed by India.
Etymology
The English word potato comes from Spanish patata. The Spanish Royal Academy says the Spanish word is a compound of the Taino batata ( sweet potato) and the Quechua papa (potato). This probably indicates that originally, the potato was regarded as a type of sweet potato rather than the other way around, despite the fact that there is actually no close relationship between the two plants at all.
Bulgarian картоф, as well as Russian картофель and German Kartoffel, derive from the Italian word tartufoli, which was given to potato because of its similarity to truffles (Italian: tartufo).
Another common name is "ground apple": pomme de terre in French, aardappel in Dutch, תפוח אדמה in Hebrew (often written just as פוד), and Erdapfel in Austrian German. An analogous name is Finnish as peruna, which comes from the old Swedish term jordpäron "earth pear". In 16th century French, pomme meant "fruit", thus pomme de terre meant "ground fruit" and was probably literally loan translated to other languages when potatoes were introduced. In Polish potato is called just ziemniaki, and in Slovak zemiak, from the word for "ground". In several northern Indian languages and in Nepali the potato is called alu/aloo and in Indonesian kentang.
Different names for the potato developed in China's various regions, the most widely used names in standard Chinese today are "horse-bell yam" (马铃薯 - mǎlíngshǔ), "earth bean" (土豆 - tǔdòu), and "foreign taro" (洋芋 - yángyù).
Description
Potato plants grow high to the ground and bear yellow to silver flowers with yellow stamens.
Potatoes are cross-pollinated mostly by bumblebees that carry pollen from other potato plants, but a substantial amount of self-fertilizing occurs as well. Any potato variety can also be propagated vegetatively by planting tubers, pieces of tubers, cut to include at least one or two eyes, or also by cuttings, a practice used in greenhouses for the production of healthy seed tubers.
Some commercial potato varieties do not produce seeds at all (they bear imperfect flowers) and are propagated only from tuber pieces. Confusingly, these tubers or tuber pieces are called "seed potatoes".
After potato plants flower, some varieties will produce small green fruits that resemble green cherry tomatoes. Each fruit can contain up to 300 true seeds. One can separate seeds from the fruits by putting them in a blender on a slow speed with some water, then leaving them in water for a day so that the seeds will sink and the rest of the fruit will float. All new potato varieties are grown from seeds, also called "true seed" or "botanical seed" to distinguish it from seed tubers. Potato fruit contains large amounts of the toxic alkaloid solanine, and is therefore unsuitable for consumption.
Origin and history
There is general agreement among contemporary botanists that the potato originated in the Andes, all the way from Colombia and Venezuela to Chile and northern Argentina, but with a concentration of genetic diversity, both in the form of cultivated and wild species, in the area of modern day Peru. The evidence thus far shows that the potato was first cultivated in Peru some 7,000 years ago.
The potatoes cultivated in the Andes are not all the same species. However, the major species grown worldwide is Solanum tuberosum (a tetraploid with 48 chromosomes). Modern varieties of this species are the most widely cultivated worldwide. There are also four diploid species (with 24 chromosomes): Solanum stenotomum, Solanum phureja, Solanum goniocalyx and Solanum ajanhuiri. There are two triploid species (with 36 chromosomes): Solanum chaucha and Solanum juzepczukii. There is one pentaploid cultivated species (with 60 chromosomes): Solanum curtilobum.
There are two major subspecies of Solanum tuberosum: andigena, or Andean; and tuberosum, or Chilean. The Andean potato is adapted to the short-day conditions prevalent in the mountainous equatorial and tropical regions where it originated. The Chilean potato is adapted to the long-day conditions prevalent in the higher latitude region of southern Chile, especially on Chiloe Island where it is thought to have originated. The Andean variety of tuberosum was the variety first introduced to Europe by way of the Canary Islands and Spain as early as 1700, and dominated European production until a few decades before the Irish Potato Famine, according to recently-published DNA analysis. The same research shows that in the early 19th century, the Chilean variety of tuberosum, adapted to long-day growing conditions, was introduced to Europe. It quickly replaced the Andean short-day variety. Today, over 99% of all cultivated potato varieties worldwide are descendants of the Chilean variety.
Historical and genetic evidence suggests that the potato reached India not very much later than Europe, taken there by either the British or the Portuguese. Genetic studies show that all 32 varieties of potato grown in India derive from the Chilean subspecies. The earliest unequivocal reference to the potato in India is in an 1847 British journal.
There are about five thousand potato varieties world wide. Three thousand of them are found in the Andes alone, mainly in Peru, Bolivia, Ecuador, Chile and Colombia. They belong to eight or nine species, depending on the taxonomic school. Apart from the five thousand cultivated varieties, there are about 200 wild species and subspecies, many of which can be cross-bred with cultivated varieties, which has been done repeatedly to transfer resistances to certain pests and diseases from the gene pool of wild species to the gene pool of cultivated potato species.
Potatoes are occasionally referred to as "Irish" potatoes in the English speaking world because in the earliest years, this signified a distinction from sweet potatoes. Potatoes were widely grown in Ireland after they were introduced, but in 1845, potato blight devastated the crop, precipitating the six-year-long Great Irish Famine.
Most modern potatoes grown in North America arrived through European settlement and not independently from the South American sources. However, at least one wild potato species, Solanum fendleri, is found as far north as Texas and used in breeding for resistance to a nematode species attacking cultivated potatoes. A secondary centre of genetic variability of the potato is Mexico, where important wild species are found that have been used extensively in modern breeding, such as the hexaploid Solanum demissum, as a source of resistance to the devastating late blight disease. Another plant native to this region, Solanum bulbocastanum, a close relative of the potato, has been used to genetically engineer the potato to effectively resist potato blight.
The potato became an important staple crop in northern Europe as the climate changed due to the Little Ice Age, when traditional crops in this region did not produce as reliably as before. At times when and where most other crops would fail, potatoes could still typically be relied upon to contribute adequately to food supplies during the colder years. The potato was not popular in France during this time, and it is believed that some of the infamous famines could have been lessened if French farmers had adopted it. Today, the potato forms an important part of the traditional cuisine of the British Isles, northern Europe, central Europe and eastern Europe. As of 2007, Germany has a higher consumption of potato per capita than any other country.
Nutrition
| Potato, raw, with peel Nutritional value per 100 g (3.5 oz) |
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| Energy 80 kcal 320 kJ | ||||||||||||||||||||||||||||||||
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| Percentages are relative to US recommendations for adults. |
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Nutritionally, potatoes are best known for their carbohydrate content (approximately 26 grams in a medium potato). Starch is the predominant form of carbohydrate found in potatoes. A small but significant portion of the starch in potatoes is resistant to enzymatic digestion in the stomach and small intestine and, thus, reaches the large intestine essentially intact. This resistant starch is considered to have similar physiological effects and health benefits of fibre (e.g., provide bulk, offer protection against colon cancer, improve glucose tolerance and insulin sensitivity, lower plasma cholesterol and triglyceride concentrations, increase satiety, and possibly even reduce fat storage) (Cummings et al. 1996; Hylla et al 1998; Raban et al. 1994). The amount of resistant starch found in potatoes is highly dependent upon preparation methods. Cooking and then cooling potatoes significantly increases resistant starch. For example, cooked potato starch contains about 7% resistant starch, which increases to about 13% upon cooling (Englyst et al. 1992).
Potatoes contain a number of important vitamins and minerals. A medium potato (150g/5.3 oz) with the skin provides 27 mg vitamin C (45% of the Daily Value (DV)), 620 mg of potassium (18% of DV), 0.2 mg vitamin B6 (10% of DV) and trace amounts of thiamin, riboflavin, folate, niacin, magnesium, phosphorus, iron, and zinc. Moreover, the fiber content of a potato with skin (2 grams) equals that of many whole grain breads, pastas, and cereals. In addition to vitamins, minerals and fibre, potatoes also contain an assortment of phytochemicals, such as carotenoids and polyphenols. The notion that “all of the potato’s nutrients” are found in the skin is an urban legend. While the skin does contain approximately half of the total dietary fibre, the majority (more than 50%) of the nutrients are found within the potato itself. The cooking method used can significantly impact the nutrient availability of the potato.
Potatoes are often broadly classified as “high” on the glycemic index (GI) and thus are frequently excluded from the diets of individuals trying to follow a “low GI” eating regimen. In fact, the GI of potatoes can vary considerably depending on the type (i.e., red vs. russet vs. white vs. Prince Edward), origin (i.e., where it was grown), preparation methods (i.e., cooking method, whether it is eaten hot or cold, whether it is mashed or cubed or consumed whole, etc), and what it is consumed with (i.e., the addition of various high fat or high protein toppings) (Fernandes et al. 2006).
Potatoes are prepared in many ways: skin-on or peeled, whole or cut up, with seasonings or without. The only requirement involves cooking to break down the starch. Most potato dishes are served hot, but some are first cooked then served cold, notably potato salad and potato chips/crisps.
Common dishes are: mashed potatoes, which are first boiled (usually peeled), and then mashed with milk or yogurt and butter; whole baked potatoes; boiled or steamed potatoes; French-fried potatoes or chips; cut into cubes and roasted; scalloped, diced, or sliced and fried (home fries); grated into small thin strips and fried (hash browns); grated and formed into dumplings, Rösti or potato pancakes. Unlike many foods, potatoes can also be easily cooked in a microwave oven and still retain nearly all of their nutritional value, provided that they are covered in ventilated plastic wrap to prevent moisture from escaping—this method produces a meal very similar to a steamed potato while retaining the appearance of a conventionally baked potato. Potato chunks also commonly appear as a stew ingredient.
Potatoes are boiled between 10 and 25 minutes, depending on size and type, to become soft.
Regional dishes
Latin America
Peruvian Cuisine naturally contains the potato as a primary ingredient in many dishes, as around 3,000 varieties of this tuber are grown there. Some of the more famous dishes include Papa a la huancaina, Papa rellena, Ocopa, Carapulcra, Causa and Cau Cau among many others.
Europe
In Britain potatoes form part of the traditional staple fish and chips. Mashed, potatoes also form a major component of several other traditional British dishes such as shepherd's pie, bubble and squeak, champ and the 'mashit tatties' ( Scots language) which accompany haggis. The Tattie scone is another popular Scottish dish containing potatoes. They are also often sautéed to accompany a meal.
Colcannon is a traditional Irish dish involving mashed potato combined with shredded cabbage and onion. Boxty pancakes are eaten all over Ireland, although associated especially with the north, and in Irish diaspora communities: they are traditionally made with grated potatoes, soaked to loosen the starch and mixed with flour, buttermilk and baking powder. A variant eaten and sold in Lancashire, especially Liverpool, is made with cooked and mashed potatoes.
In Northern Europe, especially Denmark,Norway, Sweden and Finland, newly harvested, early ripening varieties are considered a special delicacy. Boiled whole and served with dill, these "new potatoes" are traditionally consumed together with Baltic herring. In the UK, new potatoes are typically cooked with mint and served with a little melted butter - Jersey Royal potatoes are the most prized new potatoes, and have their own Protected Designation of Origin.
In Western Europe, especially in Belgium, sliced potatoes are fried to get frieten, the original French fried potatoes.
Potatoes are very popular in continental Europe as well. In Italy, they serve to make a type of pasta called gnocchi. Similarly, cooked and mashed potatoes or potato flour can be used in the knödel or dumpling eaten with or added to meat dishes all over central and Eastern Europe, but especially in Bavaria and Luxembourg. Potatoes form one of the main ingredients in many soups such as the pseudo-French vichyssoise and Albanian potato and cabbage soup. In western Norway, komle is popular.
A traditional Canary Islands dish is Canarian wrinkly potatoes or Papas arrugadas. Tortilla de patatas (potato omelete) and Patatas bravas (a dish of fried potatoes in a spicy tomato sauce) are near-universal constituent of Spanish tapas.
North America
In the United States, potatoes have become one of the most widely consumed crops, and thus have a variety of preparation methods and condiments. French fries and often hash browns are commonly found in typical American fast-food burger joints and cafeterias. One popular favorite involves a baked potato with cheddar cheese (or sour cream and chives) on top, and in New England "smashed potatoes" (a chunkier variation on mashed potatoes, retaining the peel) have great popularity. Potato flakes are popular as an instant variety of mashed potatoes, which reconstitute into mashed potatoes by adding water, plus butter & salt for taste. A regional dish of Central New York, salt potatoes are bite-sized new potatoes boiled in water saturated with salt then served with melted butter.
A traditional Acadian dish from New Brunswick is known as poutine râpée. The Acadian poutine is a ball of grated and mashed potato, salted, sometimes filled with pork in the centre, and boiled. The result is a moist ball about the size of a baseball. It is commonly eaten with salt and pepper or brown sugar. It is believed to have originated from the German Klöße, prepared by early German settlers who lived among the Acadians.
Poutine, by contrast, is a hearty serving of french fries, fresh cheese curds and hot gravy. Tracing its origins to Quebec in the 1950s, it has become popular across Canada and can usually be found where Canadians gather abroad.
Toxic compounds in potatoes
Early Rose variety
Potatoes contain glycoalkaloids, toxic compounds, of which the most prevalent are solanine and chaconine. Cooking at high temperatures (over 170 °C or 340 °F) partly destroys these. The concentration of glycoalkaloid in wild potatoes suffices to produce toxic effects in humans. Glycoalkaloids occur in the greatest concentrations just underneath the skin of the tuber, and they increase with age and exposure to light. Glycoalkaloids may cause headaches, diarrhea, cramps and in severe cases coma and death; however, poisoning from potatoes occurs very rarely. Light exposure also causes greening, thus giving a visual clue as to areas of the tuber that may have become more toxic; however, this does not provide a definitive guide, as greening and glycoalkaloid accumulation can occur independently of each other. Some varieties of potato contain greater glycoalkaloid concentrations than others; breeders developing new varieties test for this, and sometimes have to discard an otherwise promising cultivar.
Breeders try to keep solanine levels below 200 mg/kg (200 ppmw). However, when these commercial varieties turn green, even they can approach concentrations of solanine of 1000 mg/kg (1000 ppmw). In normal potatoes, however, analysis has shown solanine levels may be as little as 3.5% of the breeders' maximum, with 7–187 mg/kg being found. The National Toxicology Program suggests that the average American consumes at most 12.5 mg/day of solanine from potatoes (note that the toxic dose is actually several times this, depending on body weight). Dr. Douglas L. Holt, the State Extension Specialist for Food Safety at the University of Missouri - Columbia, notes that no reported cases of potato-source solanine poisoning have occurred in the U.S. in the last 50 years and most cases involved eating green potatoes or drinking potato-leaf tea.
Solanine is also found in other plants, mainly in the mostly-deadly nightshade family, which includes a minority of edible plants including the potato and the tomato, and other typically more dangerous plants like tobacco. This poison affects the nervous system causing weakness and confusion.
- Solanine
- List of poisonous plants
- Sites with information about the safety of green potatoes:
- http://www.straightdope.com/classics/a2_055b.html
- http://www.foodscience.afisc.csiro.au/spuds.htm
- http://www.promolux.com/english/retail_produce_greening.html
Cultivation
Washington
Fort Fairfield, Maine
Potatoes are generally grown from the eyes of another potato and not from seed. Home gardeners often plant a piece of potato with two or three eyes in a hill of mounded soil. Commercial growers plant potatoes as a row crop using seed tubers, young plants or microtubers and may mound the entire row.
At harvest time, gardeners generally dig up potatoes with a long-handled, three-prong "grape" (or graip), i.e. a spading fork, or a potato hook which is similar to the graip, except the tines are at a 90 degree angle to the handle as is the blade of a hoe. In larger plots, the plow can serve as the most expeditious implement for unearthing potatoes. Commercial harvesting is typically done with large potato harvesters which scoop up the plant and the surrounding earth. This is transported up an apron chain consisting of steel links several feet wide, which separates some of the dirt. The chain deposits into an area where further separation occurs. Different designs employ different systems at this point. The most complex designs use vine choppers and shakers, along with a blower system or "Flying Willard" to separate the potatoes from the plant. The result is then usually run past workers who continue to sort out plant material, stones, and rotten potatoes before the potatoes are continuously delivered to a wagon or truck. Further inspection and separation occurs when the potatoes are unloaded from the field vehicles and put into storage.
Correct potato husbandry is an arduous task in the best of circumstances. Good ground preparation, harrowing, plowing, and rolling are always needed, along with a little grace from the weather and a good source of water. Three successive plowings, with associated harrowing and rolling, are desirable before planting. Eliminating all root-weeds is desirable in potato cultivation. Potatoes are the most fruitful of the root crops, but much care and consideration is needed to keep them satisfied and fruitful.
It is important to harvest potatoes before heavy frosts begin, since field frost damages potatoes in the ground, and even cold weather makes potatoes more susceptible to bruising and possibly later rotting which can quickly ruin a large stored crop.
Seed potato crops are 'rogued' in some countries to eliminate diseased plants or those of a different variety from the seed crop.
Storage facilities need to be carefully designed to keep the potatoes alive and slow the natural process of decomposition, which involves the breakdown of starch. It is crucial that the storage area is dark, well ventilated and for long-term storage maintained at temperatures near 40°F (4°C). For short-term storage prior to cooking, temperatures of about 45-50°F (7-10°C) are preferred. Temperatures below 40°F (4°C) convert potatoes' starch into sugar, which alters their taste and cooking qualities and leads to higher acrylamide levels in the cooked product, especially in deep-fried dishes.
Under optimum conditions possible in commercial warehouses, potatoes can be stored for up to six months, but several weeks is the normal shelf life in homes. If potatoes develop green areas or start to sprout, these areas should be trimmed before using.
FAO reports that the world production of potatoes in 2005 was 319 million tonnes. The largest producer, China, accounted for one-fourth of the global output followed by Russia and India.
Varieties
Potatoes have been bred into many standard or well-known varieties, each of which have particular agricultural or culinary attributes. Varieties are generally categorized into a few main groups, such as Russets, Reds, Whites, Yellows (aka Yukons), and Purples based on common characteristics. Popular varieties found in markets may include:
- Désirée
- Fianna
- King Edward
- Kipfler
- New
- Nicola
- Pink Eye
- Pink Fir Apple
- Red Pontiac
- Russet Burbank
- Spunta
Genetic research on the potato has resulted in at least one genetically-modified variety, the New Leaf, owned by Monsanto corporation.
Potatoes of all varieties are generally cured after harvest to thicken the skin. Prior to curing, the skin is very thin and delicate. These potatoes are sometimes sold as "New Potatoes" and are particularly flavorful. New potatoes are often harvested by the home gardener or farmer by "grabbling", i.e. pulling out the young tubers by hand while leaving the plant in place. In additions, markets may sometimes present various thin-skinned potato varieties as "new potatoes".
Some horticulturists sell chimeras, made by grafting a tomato plant onto a potato plant, producing both edible tomatoes and potatoes. This practice is not very widespread.
Philippines
On September 22, 2007, Benguet State University (BSU) announce that 4 potato varieties -- Igorota, Solibao, Ganza and a 4th one yet to be given an official tag -- possess more than 18% dry matter content required by fast-food chains to make crispy and sturdy French fries.
Pests
A major pest of potato plants is the Colorado potato beetle.
The potato root nematode is a microscopic worm that thrives on the roots, thus causing the potato plants to wilt. Since its eggs can survive in the soil for several years, crop rotation is recommended.
Other pests include Aphids, both the Green Peach Aphid and the Potato Aphid. Beetleafhoppers, Thrips, and Mites are also very common potato insect pests.
A major disease of potato plants is potato blight caused by Phytophthora infestans.
Other major diseases include Rhizoctonia, Sclerotinia, Black Leg, Powdery Mildew, Powdery Scab, Leafroll Virus, Purple Top, and others.
Potatoes and Art
The potato has been an essential crop in the Andes since the pre-Columbian Era. The Moche culture from Northern Peru made ceramics from earth, water, and fire. This pottery was a sacred substance, formed in significant shapes and used to represent important themes. Potatoes are represented anthropomorphically as well as naturally.
Maine companies are exploring the possibilities of using waste potatoes to obtain polylactic acid for use in plastic products.
International Year of the Potato
The United Nations have officially declared the year 2008 the International Year of the Potato in order to “increase awareness of the importance of the potato as a food in developing nations”. There was already the International Rice Year in 2004.