Pea

Pea
Peas are contained within a pod
Pea plant: Pisum sativum
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
Order:	Fabales
Family:	Fabaceae
Genus:	Pisum
Species:	P. sativum
Binomial name
Pisum sativum L.
Synonyms[1]
Lathyrus oleraceus Lam. Pisum arvense L. Pisum biflorum Raf. Pisum elatius M.Bieb. Pisum humile Boiss. & Noe Pisum vulgare Jundz.

Pisum sativum - MHNT

The pea is most commonly the small spherical seed or the seed-pod of the pod fruit Pisum sativum.^[2] Each pod contains several peas. Pea pods are botanically fruit,^[3] since they contain seeds and developed from the ovary of a (pea) flower. The name is also used to describe other edible seeds from the Fabaceae such as the pigeon pea (Cajanus cajan), the cowpea (Vigna unguiculata), and the seeds from several species of Lathyrus.

P. sativum is an annual plant, with a life cycle of one year. It is a cool season crop grown in many parts of the world; planting can take place from winter to early summer depending on location. The average pea weighs between 0.1 and 0.36 grams.^[4] The immature peas (and in snow peas the tender pod as well) are used as a vegetable, fresh, frozen or canned; varieties of the species typically called field peas are grown to produce dry peas like the split pea shelled from the matured pod. These are the basis of pease porridge and pea soup, staples of medieval cuisine; in Europe, consuming fresh immature green peas was an innovation of Early Modern cuisine.

The wild pea is restricted to the Mediterranean basin and the Near East. The earliest archaeological finds of peas date from the late neolithic era of current Greece, Syria, Turkey and Jordan. In Egypt, early finds date from ca. 4800–4400 BC in the Nile delta area, and from ca. 3800–3600 BC in Upper Egypt. The pea was also present in Georgia in the 5th millennium BC. Farther east, the finds are younger. Peas were present in Afghanistan ca. 2000 BC, in Harappa, Pakistan, and in northwest India in 2250–1750 BC. In the second half of the 2nd millennium BC, this pulse crop appears in the Gangetic basin and southern India.^[5]

Description

A pea is a most commonly green, occasionally golden yellow,^[6] or infrequently purple^[7] pod-shaped vegetable, widely grown as a cool season vegetable crop. The seeds may be planted as soon as the soil temperature reaches 10 °C (50 °F), with the plants growing best at temperatures of 13 to 18 °C (55 to 64 °F). They do not thrive in the summer heat of warmer temperate and lowland tropical climates, but do grow well in cooler, high altitude, tropical areas. Many cultivars reach maturity about 60 days after planting.

Worldwide pea yield

Peas have both low-growing and vining cultivars. The vining cultivars grow thin tendrils from leaves that coil around any available support and can climb to be 1–2 m high. A traditional approach to supporting climbing peas is to thrust branches pruned from trees or other woody plants upright into the soil, providing a lattice for the peas to climb. Branches used in this fashion are sometimes called pea brush. Metal fences, twine, or netting supported by a frame are used for the same purpose. In dense plantings, peas give each other some measure of mutual support. Pea plants can self-pollinate.^[8]

History

Pea in a painting by Mateusz Tokarski, ca. 1795 (National Museum in Warsaw).

In early times, peas were grown mostly for their dry seeds.^[9] From plants growing wild in the Mediterranean basin, constant selection since the Neolithic dawn of agriculture^[10] improved their yield. In the early 3rd century BC Theophrastus mentions peas among the pulses that are sown late in the winter because of their tenderness.^[11] In the first century AD Columella mentions them in De re rustica, and Roman legionaries still gathered wild peas from the sandy soils of Numidia and Palestine, to supplement their rations.

Lindsey Davis' historically accurate crime novel set in Ancient Rome, The Silver Pigs, notes a recipe for mushy peas was named after Emperor Vitellius. (Chapter XX, p. 3)^[12]

In the Middle Ages, field peas are constantly mentioned, as they were the staple that kept famine at bay, as Charles the Good, count of Flanders noted explicitly in 1124.^[13] In the 13th century the poet Guillaume de Villeneuve noted

J'ay pois en cosse touz noviaux

among the street cries of Paris.^[14]

Green "garden" peas, eaten immature and fresh, were an innovative luxury of Early Modern Europe. In England, the distinction between "field peas" and "garden peas" dates from the early 17th century: John Gerard and John Parkinson both mention garden peas. Sugar peas, which the French soon called mange-tout, for they were consumed pods and all, were introduced to France from the market gardens of Holland in the time of Henri IV, through the French ambassador. Green peas were introduced from Genoa to the court of Louis XIV of France in January 1660, with some staged fanfare; a hamper of them were presented before the King, and then were shelled by the Sovoyan comte de Soissons, who had married a niece of Cardinal Mazarin; little dishes of peas were then presented to the King, the Queen, Cardinal Mazarin and Monsieur, the king's brother.^[15] Immediately established and grown for earliness warmed with manure and protected under glass, they were still a luxurious delicacy in 1696, when Mme de Maintenon and Mme de Sevigné each reported that they were "a fashion, a fury."^[16]

Modern split peas, with their indigestible skins rubbed off, are a development of the later 19th century.

Modern culinary use

Fresh peas for sale in their pods on a UK market stall

Frozen green peas

In modern times peas are usually boiled or steamed, which breaks down the cell walls and makes the taste sweeter and the nutrients more bioavailable. Along with broad beans and lentils, these formed an important part of the diet of most people in the Middle East, North Africa and Europe during the Middle Ages.^[17] By the 17th and 18th centuries, it had become popular to eat peas "green", that is, while they are immature and right after they are picked. This was especially true in France and England, where the eating of green peas was said to be "both a fashion and a madness".^[18] New cultivars of peas were developed by the English during this time, which became known as "garden" or "English" peas. The popularity of green peas spread to North America. Thomas Jefferson grew more than 30 cultivars of peas on his estate.^[19] With the invention of canning and freezing of foods, green peas became available year-round, and not just in the spring as before.

Peas in fried rice

Fresh peas are often eaten boiled and flavored with butter and/or spearmint as a side dish vegetable. Salt and pepper are also commonly added to peas when served. Fresh peas are also used in pot pies, salads and casseroles. Pod peas (particularly sweet cultivars called mange tout and "sugar peas", or the flatter "snow peas," called hé lán dòu, 荷兰豆 in Chinese) are used in stir-fried dishes, particularly those in American Chinese cuisine.^[20] Pea pods do not keep well once picked, and if not used quickly, are best preserved by drying, canning or freezing within a few hours of harvest.

In India, fresh peas are used in various dishes such as aloo matar (curried potatoes with peas) or matar paneer (paneer cheese with peas), though they can be substituted with frozen peas as well. Peas are also eaten raw, as they are sweet when fresh off the bush. Split peas are also used to make dhal, particularly in Guyana, and Trinidad, where there is a significant population of Indians.

Dried peas are often made into a soup or simply eaten on their own. In Japan, China, Taiwan and some Southeast Asian countries, including Thailand, the Philippines and Malaysia, peas are roasted and salted, and eaten as snacks. In the Philippines, peas, while still in their pods, are a common ingredient in viands and pansit. In the UK, dried yellow split peas are used to make pease pudding (or "pease porridge"), a traditional dish. In North America, a similarly traditional dish is split pea soup.

Pea soup is eaten in many other parts of the world, including northern Europe, parts of middle Europe, Russia, Iran, Iraq and India.^[21] In Sweden it is called ärtsoppa, and is eaten as a traditional Swedish food which predates the Viking age. This food was made from a fast-growing pea that would mature in a short growing season. Ärtsoppa was especially popular among the many poor who traditionally only had one pot and everything was cooked together for a dinner using a tripod to hold the pot over the fire.

In Chinese cuisine, the tender new growth [leaves and stem] (豆苗; dòu miáo) are commonly used in stir-fries. Much like picking the leaves for tea, the farmers pick the tips off of the pea plant.

In Greece, Tunisia, Turkey, Cyprus, and other parts of the Mediterranean, peas are made into a stew with meat and potatoes.

In Hungary and Serbia, pea soup is often served with dumplings and spiced with hot paprika.

In the United Kingdom, dried, rehydrated and mashed marrowfat peas, known by the public as mushy peas, are popular, originally in the north of England, but now ubiquitously, and especially as an accompaniment to fish and chips or meat pies, particularly in fish and chip shops. Sodium bicarbonate is sometimes added to soften the peas. In 2005, a poll of 2,000 people revealed the pea to be Britain's seventh favourite culinary vegetable.^[22]

Processed peas are mature peas which have been dried, soaked and then heat treated (processed) to prevent spoilage—in the same manner as pasteurising. Cooked peas are sometimes sold dried and coated with wasabi, salt, or other spices.

Manufacturing frozen peas

In order to freeze and preserve peas, they must first be grown, picked, and shelled. Usually, the more tender the peas are, the more likely the peas will be used in the final product. The peas must be put through the process of freezing shortly after being picked so that they do not spoil too soon. Once the peas have been selected, they are placed in ice water and allowed to cool. After, they are sprayed with water to remove any residual dirt or dust that may remain on the vegetable. The next step in processing peas is blanching. The peas are boiled for a few minutes to remove any enzymes that may shorten the shelf life of the pea. The peas are then cooled and removed from the water. The final step to freezing peas is the actual freezing to produce the final product.^[23] This step may vary largely from company to company. Some companies may freeze their peas by air blast freezing, where the vegetables are put through a tunnel at high speeds and frozen by cold air . Another method of freezing peas is by placing the product on a metal plate which was cooled by the compound Ammonia. Finally, the peas are packaged and shipped out for retail.

Grading

Pea grading involves sorting peas by size, in which the smallest peas are graded as the highest quality for their tenderness.^[24] Brines may be used, in which peas are floated, from which their density can be determined.^[24]

Nutritional value

Peas are starchy, but high in fiber, protein, vitamin A, vitamin B6, vitamin C, vitamin K, phosphorus, magnesium, copper, iron, zinc and lutein.^[25] Dry weight is about one-quarter protein and one-quarter sugar.^[26] Pea seed peptide fractions have less ability to scavenge free radicals than glutathione, but greater ability to chelate metals and inhibit linoleic acid oxidation.^[27]

Varieties

There are many varieties (cultivars) of garden peas. Some of the most common varieties are listed here. PMR indicates some degree of powdery mildew resistance; afila types, also called semi-leafless, have clusters of tendrils instead of leaves.^[28] Unless otherwise noted these are so called dwarf varieties which grow to an average height of about 1m. Extra dwarf are suitable for container growing, reaching only about 25 cm. Semi-tall reaches about 1.5m and tall grows to about 2m.

• Alaska, 55 days (smooth seeded)
• Tom Thumb / Half Pint, 55 days (heirloom, extra dwarf)^[29]
• Thomas Laxton (heirloom) / Laxton's Progress / Progress #9, 60–65 days
• Mr. Big, 60 days, 2000 AAS winner
• Little Marvel, 63 days, 1934 AAS winner
• Early Perfection, 65 days^[30]
• Kelvedon Wonder, 65 days, 1997 RHS AGM winner^[31]
• Sabre, 65 days, PMR
• Homesteader / Lincoln, 67 days (heirloom, known as Greenfeast in Australia and New Zealand)
• Miragreen, 68 days (semi-tall climber)
• Serge, 68 days, PMR, afila
• Wando, 68 days
• Green Arrow, 70 days
• Recruit, 70 days, PMR, afila^[32]
• Tall Telephone / Alderman, 75 days (heirloom, tall climber)

Other variations of P. sativum include:

• Pisum sativum var. macrocarpon is commonly known as the snow pea.
• Pisum sativum var. macrocarpon ser. cv. is known as the sugar or snap pea.

Both of these are eaten whole before the pod reaches maturity and are hence also known as mange-tout, French for "eat all". The snow pea pod is eaten flat, while in sugar/snap peas, the pod becomes cylindrical, but is eaten while still crisp, before the seeds inside develop.

Pests and diseases

A variety of diseases affect peas through a number of pathogens, including insects, viruses, bacteria and fungi.^[33] In particular, virus disease of peas has worldwide economic importance.^[34]

Additionally, insects such as the pea leaf weevil (Sitona lineatus) can damage peas and other pod fruits. The pea leaf weevil is native to Europe, but has spread to other places such as Alberta, Canada. They are about 3.5 millimetres (0.14 in)—5.5 millimetres (0.22 in) long and are distinguishable by three light-coloured stripes running length-wise down the thorax. The weevil larvae feed on the root nodules of pea plants, which are essential to the plants' supply of nitrogen, and thus diminish leaf and stem growth. Adult weevils feed on the leaves and create a notched, "c-shaped" appearance on the outside of the leaves.^[35]

Peas in science

Pea flowers

In the mid-19th century, Austrian monk Gregor Mendel's observations of pea pods led to the principles of Mendelian genetics, the foundation of modern genetics.^[36] He ended up growing and examining about 28,000 pea plants in the course of his experiments.^[37] Mendel chose peas for his experiments because he could grow them easily, develop pure-bred strains, protect them from cross-pollination, and control their pollination. Mendel cross-bred tall & dwarf pea plants, green & yellow peas, purple & white flowers, wrinkled & smooth peas, and a few other traits. He then observed the resulting offspring. In each of these cases, one trait is dominant and all the offspring, or Filial-1 (abbreviated F₁) generation, showed the dominant trait. Then he crossed members of the F₁ generation together and observed their offspring, the Filial-2 (abbreviated F₂) generation. The F₂ plants had the dominant trait in approximately a 3:1 ratio. Mendel reasoned that each parent had a 'vote' in the appearance of the offspring and the non-dominant or recessive trait appeared only when it was inherited from both parents. He did further experiments that showed each trait is separately inherited. Unwittingly, Mendel had solved a major problem with Charles Darwin's theory of evolution: how could new traits be preserved and not blended back into the population? But Darwin never learned about it. Mendel's work was published in an obscure Austrian journal and was not rediscovered until about 1900.^[38]

Peas in medicine

Some people are allergic to peas, as well as lentils. Favism, or Fava-bean-ism, is a genetic deficiency that affects Jews and other descendents of the Mediterranean with an allergic-like reaction. The reaction to eating most, if not all, beans is hemolytic anemia, and in severe cases a delayed reaction of acute kidney injury.^[39][40][41]

Nitrogen-fixing ability

Peas, like many legumes, contain symbiotic bacteria called Rhizobia within root nodules of their root systems. These bacteria have the special ability of fixing nitrogen from atmospheric, molecular nitrogen (N₂) into ammonia (NH₃).^[42] The chemical reaction is:

Ammonia is then converted to another form, ammonium (NH₄⁺), usable by (some) plants by the following reaction:

This arrangement means that the root nodules are sources of nitrogen for peas and many legumes, making them relatively rich in plant proteins. All proteins contain nitrogenous amino acids. Nitrogen is therefore a necessary ingredient in the production of proteins. Hence, peas and many legumes are among the best sources of plant protein.

When a pea plant dies in the field, for example following the harvest, all of its remaining nitrogen, incorporated into amino acids inside the remaining plant parts, is released back into the soil. In the soil, the amino acids are converted to nitrate (NO₃⁻), making the nitrogen available to other plants, thereby serving as fertilizer for future crops.^[43][44]

Bioplastics

Bioplastics can be made using pea starch.

Etymology

The term pea originates from the Latin word pisum, which is the latinisation of the Greek πίσον (pison), neuter of πίσος (pisos) "pea".^[45][46] It was adopted into English as the noun pease (plural peasen), as in pease pudding. However, by analogy with other plurals ending in -s, speakers began construing pease as a plural and constructing the singular form by dropping the -s, giving the term pea. This process is known as back-formation.

The name marrowfat pea for mature dried peas is recorded by the Oxford English Dictionary as early as 1733. The fact that an export cultivar popular in Japan is called Maro has led some people to assume mistakenly that the English name marrowfat is derived from Japanese.

Pea festival

The annual 'Peasenhall Pea Festival' in the English village of Peasenhall, Suffolk attracts hundreds of visitors every year, with events such as Pea Shooting, the World Pea Podding Championships and National Pea Eating competition. In 2012, the Pea Festival had an OlymPEAn theme, celebrating the London 2012 Olympics.

See also

• Black-eyed pea
• Black pea
• Chickpea
• Dixie lee pea
• Sweet pea

Notes

References

• European Association for Grain Legume Research (AEP). Pea. http://www.grainlegumes.com/default.asp?id_biblio=52 .
• Hernández Bermejo, J. E. & León, J., (1992). Neglected crops: 1492 from a different perspective, Food and Agricultural Organization of the United Nations (FAO) Contents
• Muehlbauer, F. J. and Tullu, A., (1997). Pisum sativum L. Purdue University. Pea
• Oelke, E. A., Oplinger E. S., et al. (1991). Dry Field Pea. University of Wisconsin.Dry Field Pea

External links

Wikimedia Commons has media related to Pisum sativum.

Wikibooks Cookbook has a recipe/module on Pea

• Sorting Pisum names
• USDA plant profile
• http://www.nal.usda.gov/fnic/foodcomp/search/