Potato

June 30th, 2007

Botanical Name: Solanum tuberosum (LINN.)
Family: N.O. Solanaceae
Part Used: Edible tubers.
The potato (Solanum tuberosum) is a perennial plant of the Solanaceae, or nightshade, family, commonly grown for its starchy tuber. Potatoes are the world’s most widely grown tuber crop, and the fourth largest food crop in terms of fresh produce â€” after rice, wheat, and maize (’corn’). The potato was domesticated in southern Peru and northern Bolivia and is important to the culture of the Andes, where farmers grow many different varieties that have a remarkable diversity of colors and shapes. In pre-Colombian times they were also widely cultivated on Chiloe Island, in Chile. Potatoes spread from South America to Spain and from there to the rest of the world after European colonization in the late 1400s and early 1500s. They soon became an important field crop.

For instance, the potato was a staple food for sailors in Spanish ships. After the wreck of the Spanish Armada in 1588, English coastal villagers rescued potatoes and planted them.
In 1845, a fungal disease, Phytophthora infestans, also known as late blight, spread rapidly through the poorer communities of western Ireland, resulting in the Irish Potato Famine. Unfortunately the local population had begun to rely on the potato as a staple food and when crops failed, year after year, huge numbers of people died. Others emigrated, largely to the United States, blaming the British government for the situation.
The potato is also strongly associated with Idaho, Maine, Prince Edward Island, Ireland, Jersey and Russia because of its large role in the agricultural economy and/or history of these regions.

For both culinary & botanical purposes, it is a vegetable.

Description of Potato plant:
Potato plants grow low to the ground and bear white to purple flowers with yellow stamens.
Potato flowers are cross-pollinated by insects, mostly bumble bees, 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.

Flowers of a potato plant.

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 look similar to green cherry tomatoes. These produce seeds like other fruits. Each of the fruits 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. However, some horticulturists sell chimeras made by grafting a tomato plant onto a potato plant, which can produce both edible tomatoes and potatoes although that practice is not very widespread.

History & Origin:
There is general agreement between contemporary botanists that the potato originated in the Andes, all the way from Colombia to 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 potatoes cultivated in the Andes are not all the same species. The major species is Solanum tuberosum ssp. andigena (a tetraploid with 48 chromosomes,) then there are four diploid species (with 24 chromosomes) by the names of Solanum stenotomum, Solanum phureja, Solanum goniocalyx and Solanum ajanhuiri. There are two triploid species (with 36 chromosomes) Solanum chaucha and Solanum juzepczukii, and finally, there is one pentaploid cultivated species (with 60 chromosomes) called Solanum curtilobum.

Andean potatoes are adapted to short day conditions and Chilean potatoes to long day conditions. There is sufficient evidence that the tetraploid Andean short day potato was the one that first arrived in Southern Spain in about 1565, from where it spread to the rest of Europe, adapting to European long day conditions in a period of about two hundred years. In order to botanically distinguish potatoes adapted to short days from those thriving and producing tubers under long day conditions, Solanum tuberosum has been split into two subspecies by present-day taxonomists, Solanum tuberosum ssp. tuberosum (adapted to long days) and Solanum tuberosum ssp. andigena (adapted to short days.) Apart from their different photoperiodic reaction, these two subspecies are also distinct morphologically, you have to be an experienced taxonomist though to spot those differences. Russian taxonomists have, in fact, created two different species in the early part of the 20th century, Solanum tuberosum and Solanum andigenum, to mark the same distinction. The process of adaptation to long days has happened once before as the potato moved from the Andes to the south of the continent. This was before the Europeans arrived in South America. Chile still has a large amount of valuable potato germplasm adapted to long days.

Historical and genetic evidence suggests that the potato reached India not very much later than Europe, probably taken there by the Portuguese. In isolated areas in the Himalayas of India and Nepal, so called “desi” potatoes are still grown, and they are very similar to the short day adapted modern day Andean potato, Solanum tuberosum ssp. andigena.

There are about five thousand potato varieties world wide, three thousand of them are found in the Andes alone, mainly in Peru, Bolivia, Ecuador and Colombia. They belong to eight or nine species, depending on your taxonomic school. Apart from the five thousand cultivated varieties, there are about 200 wild species, many of which can be cross-bred with cultivated species, which has been done repeatedly to transfer resistances to certain pests and diseases from the genepool of wild to the genepool of cultivated potato species. The list of varieties found in European, North American or Asian markets is very limited, and these varieties are all of the same species, Solanum tuberosum ssp. tuberosum.

Food Value:
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 fiber (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 fiber, potatoes also contain an assortment of phytochemicals, such as carotenoids and polyphenols. The notion that â€œall of the potatoâ€™s nutrientsâ€ are found in the skin is a myth. While the skin does contain approximately half of the total dietary fiber, 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.

New and fingerling potatoes offer the advantage that they contain fewer toxic chemicals. Such potatoes offer an excellent source of nutrition. Peeled, long-stored potatoes have less nutritional value, although they still have potassium and vitamin B.

Potatoes are often broadly classified as â€œhighâ€ on the glycemic index (GI) and thus are frequently excluded from the diets of individuals trying to follow a â€œlow GIâ€ 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).

Constituents:

The tuber is composed mainly of starch, which affords animal heat and promotes fatness, but the proportion of muscle-forming food is very small - it is said that 10 1/2 lb. of the tubers are only equal in value to 1 lb. of meat. The raw juice of the Potato contains no alkaloid, the chief ingredient being potash salts, which are present in large quantity. The tuber also contains a certain amount of citric acid - which, like Potash, is antiscorbutic - and phosphoric acid, yielding phosphorus in a quantity less only than that afforded by the apple and by wheat.

It is of paramount importance that the valuable potash salts should be retained by the Potato during cooking. If peeled and then boiled, the tubers lose as much as 33 per cent of potash and 23 per cent of phosphoric acid, and should, therefore, invariably be boiled or steamed with their coats on. Too much stress cannot be laid on this point. Peeled potatoes have lost half their food-value in the water in which they have been boiled.

The Potato is not only important as a valuable article of diet, but has many other uses, both medicinal and economic:

To carry a raw potato in the pocket was an old-fashioned remedy against rheumatism that modern research has proved to have a scientific basis. Ladies in former times had special bags or pockets made in their dresses in which to carry one or more small raw potatoes for the purpose of avoiding rheumatism if predisposed thereto. Successful experiments in the treatment of rheumatism and gout have in the last few years been made with preparations of raw potato juice. In cases of gout, rheumatism and lumbago the acute pain is much relieved by fomentations of the prepared juice followed by an application of liniment and ointment. Sprains and bruises have also been successfully treated by the Potato-juice preparations, and in cases of synovitis rapid absorption of the fluid has resulted. Although it is not claimed that the treatment in acute gout will cure the constitutional symptoms, local treatment by its means relieves the pain more quickly than other treatment.

Potato starch is much used for determining the diastatic value of malt extract.

Hot potato water has in years past been a popular remedy for some forms of rheumatism, fomentations to swollen and painful parts, as hot as can be borne, being applied from water in which 1 lb. of unpeeled potatoes, divided into quarters, has been boiled in 2 pints slowly boiled down to 1 pint Another potato remedy for rheumatism was made by cutting up the tubers, infusing them together with the fresh stalks and unripe berries for some hours in cold water, and applying in the form of a cold compress. The potatoes should not be peeled.

Uncooked potatoes, peeled and pounded in a mortar, and applied cold, have been found to make a very soothing plaster to parts that have been scalded or burnt.

The mealy flour of baked potato, mixed with sweet oil, is a very healing application for frost-bites. In Derbyshire, hot boiled potatoes are used for corns.

Boiled with weak sulphuric acid, potato starch is changed into glucose, or grape sugar, which by fermentation yields alcohol this spirit being often sold under the name of British Brandy.

A volatile oil - chemically termed Amylic alcohol, in Germany known as FuselÃ¶l - is distilled by fermentation from potato spirit.

Although young potatoes contain no citric acid, the mature tubers yield enough even for commercial purposes, and ripe potato juice is an excellent cleaner of silks, cottons and woollens.

A fine flour is prepared from the Potato, and more used on the Continent than in this country for cake-making.

Potato Derivative Used to Stop Bleeding

Toxic Compoumds in Potatoes:
Potatoes contain glycoalkaloids, toxic compounds, of which the most prevalent are solanine and chaconine. Cooking at high temperatures (over 170 Â°C or 340 Â°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 0.2 mg/g (200 ppmw). However, when even these commercial varieties turn green, they can approach concentrations of solanine of 1 mg/g (1000 ppmw). The National Toxicology Program suggests that the average American consumes at most 12.5 mg/person/day of solanine from potatoes. 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.

Cultivation:
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.

Resources:

http://en.wikipedia.org/wiki/Potato

http://www.botanical.com/botanical/mgmh/p/potato65.html