Lettuce
From Wikipedia, the free encyclopedia
For other uses, see Lettuce (disambiguation).
| Lettuce | |
|---|---|
| Iceberg lettuce field | |
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Eudicots |
| (unranked): | Asterids |
| Order: | Asterales |
| Family: | Asteraceae |
| Genus: | Lactuca |
| Species: | L. sativa |
| Binomial name | |
| Lactuca sativa L. | |
| Synonyms[1][2] | |
| |
Lettuce (Lactuca sativa) is an annual plant of the aster or sunflower family Asteraceae. It is most often grown as a leaf vegetable, but sometimes for its stem and seeds. Lettuce was first cultivated by the ancient Egyptians who turned it from a weed, whose seeds were used to produce oil, into a plant grown for its leaves. Lettuce spread to the Greeks and Romans, the latter of whom gave it the name "lactuca", from which the English "lettuce" is ultimately derived. By 50 AD, multiple types were described, and lettuce appeared often in medieval writings, including several herbals. The 16th through 18th centuries saw the development of many varieties in Europe, and by the mid-18th century cultivars were described that can still be found in gardens. Europe and North America originally dominated the market for lettuce, but by the late 1900s the consumption of lettuce had spread throughout the world.
Generally grown as a hardy annual, lettuce is easily cultivated, although it requires relatively low temperatures to prevent it from flowering quickly. It can be plagued with numerous nutrient deficiencies, as well as insect and mammal pests and fungal and bacterial diseases. L. sativa crosses easily within the species and with some other species within the Lactuca genus; although this trait can be a problem to home gardeners who attempt to save seeds, biologists have used it to broaden the gene pool of cultivated lettuce varieties. World production of lettuce and chicory for calendar year 2010 stood at 23,620,000 metric tons (23,250,000 long tons; 26,040,000 short tons), over half of which came from China.
Lettuce is most often used for salads, although it is also seen in other kinds of food, such as soups, sandwiches and wraps. One type is grown for its stems, which are eaten either raw or cooked. Lettuce is a good source of vitamin A and potassium, as well as a minor source for several other vitamins and nutrients. Despite its beneficial properties, lettuce when contaminated is often a source of bacterial, viral and parasitic outbreaks in humans, including E. coli and Salmonella. In addition to its main use as a leafy green, it has also gathered religious and medicinal significance over centuries of human consumption.
Taxonomy and etymology
Lactuca sativa is a member of the Lactuca (lettuce) genus and the Asteraceae (sunflower or aster) family.[3] The species was first described in 1753 byCarl Linnaeus in the second volume of his Species Plantarum.[4] Synonyms for L. sativa include Lactuca scariola var. sativa,[1] L. scariola var. integrataand L. scariola var. integrifolia.[5] L. scariola is itself a synonym for L. serriola, the common wild or prickly lettuce.[2] L. sativa also has many identified taxonomic groups, subspecies and varieties, which delineate the various cultivar groups of domesticated lettuce.[6] Lettuce is closely related to severalLactuca species from southwest Asia; the closest relationship is to L. serriola, an aggressive weed common in temperate and subtropical zones in much of the world.[7]
The Romans referred to lettuce as lactuca (lac meaning milk in Latin), an allusion to the white substance, now called latex, exuded by cut stems.[8]This word has become the genus name, while sativa (meaning "sown" or "cultivated") was added to create the species name.[9] The current wordlettuce, originally from Middle English, came from the Old French letues or laitues, which derived from the Roman name.[10] The name romaine came from that type's use in the Roman papal gardens, while cos, another term for romaine lettuce, came from the earliest European seeds of the type from the Greek island of Cos, a center of lettuce farming in the Byzantine period.[11]
Nutrition and health
| Nutritional value per 100 g (3.5 oz) | |
|---|---|
| Energy | 55 kJ (13 kcal) |
| Carbohydrates | 2.23 g |
| - Sugars | 0.94 |
| - Dietary fibre | 1.1 g |
| Fat | 0.22 g |
| Protein | 1.35 g |
| Water | 95.63 g |
| Vitamin A equiv. | 166 μg (21%) |
| - beta-carotene | 1987 μg (18%) |
| - lutein and zeaxanthin | 1223 μg |
| Thiamine (vit. B1) | 0.057 mg (5%) |
| Riboflavin (vit. B2) | 0.062 mg (5%) |
| Pantothenic acid (B5) | 0.15 mg (3%) |
| Vitamin B6 | 0.082 mg (6%) |
| Folate (vit. B9) | 73 μg (18%) |
| Vitamin C | 3.7 mg (4%) |
| Vitamin E | 0.18 mg (1%) |
| Vitamin K | 102.3 μg (97%) |
| Calcium | 35 mg (4%) |
| Iron | 1.24 mg (10%) |
| Magnesium | 13 mg (4%) |
| Manganese | 0.179 mg (9%) |
| Phosphorus | 33 mg (5%) |
| Potassium | 238 mg (5%) |
| Sodium | 5 mg (0%) |
| Zinc | 0.2 mg (2%) |
| Link to USDA Database entry Percentages are relative to US recommendations for adults. Source: USDA Nutrient Database | |
Depending on the variety, lettuce is a good source of vitamin A, vitamin K and potassium, with higher concentrations of vitamin A found in darker green lettuces. It also provides some dietary fiber (concentrated in the spine and ribs), carbohydrates, protein and a small amount of fat. With the exception of the iceberg type, lettuce also provides some vitamin C, calcium, iron and copper, with vitamins and minerals largely found in the leaf.[30] Lettuce naturally absorbs and concentrates lithium.[45]
Food-borne illness
Although most food-borne pathogens can survive on stored lettuce, they tend to decline in number during the storage period. The exception to this isListeria monocytogenes, the causative agent of listeriosis, which multiplies in storage. However, despite very high levels of the bacteria being found on ready-to-eat lettuce products, a 2008 study found no incidences of food-borne illness related to listeriosis. The researcher posited that this may be due to the product's short shelf life, indigenous microflora competing with the Listeria bacteria or possible properties within the lettuce that cause the bacteria to be unable to cause listeriosis.[46]
Other bacteria found on lettuce include Aeromonas species, which have not been linked to any outbreaks; Campylobacter species, which causecampylobacteriosis and Yersinia intermedia and Yersinia kristensenii (species of Yersinia), which have been found mainly in lettuce.[47] Lettuce has been linked to numerous outbreaks of the bacteria E. coli O157:H7 and Shigella; the plants were most likely contaminated through contact with animal feces.[48] A 2007 study determined that the vacuum cooling method, especially prevalent in the California lettuce industry, increased the uptake and survival rates of E. coli O157:H7.[49] Salmonella bacteria, including the uncommon Salmonella braenderup type, have also caused outbreaks traced to contaminated lettuce.[50] Viruses, including hepatitis A, calicivirus and a Norwalk-like strain, have been found in lettuce. The vegetable has also been linked to outbreaks of parasitic infestations, including Giardia lamblia.[47]
Religious and medicinal lore
In addition to its usual purpose as an edible leafy vegetable, lettuce has had a number of uses in ancient (and even some more modern) times as a medicinal herb and religious symbol. For example, ancient Egyptians thought lettuce to be a symbol of sexual prowess[41] and a promoter of love and childbearing in women. The Romans likewise claimed that it increased sexual potency.[51] In contrast, the ancient Greeks connected the plant with male impotency,[8] and served it during funerals (probably due to its role in the myth of Adonis's death), and British women in the 1800s believed it would cause infertility and sterility. Lettuce has mild narcotic properties – it was called "sleepwort" by the Anglo-Saxons because of this attribute – although the cultivated L. sativa has lower levels of the narcotic than its wild cousins.[51] This narcotic effect is a property of two sesquiterpene lactones which are found in the white liquid (latex) in the stems of lettuce,[28] called lactucarium or "lettuce opium".
Lettuce extracts are sometimes used in skin creams and lotions for treating sunburn and rough skin. It was once thought to be useful in relieving liverissues. Some American settlers claimed that smallpox could be prevented through the ingestion of lettuce,[51] and an Iranian belief suggested consumption of the seeds when afflicted with typhoid.[52] Folk medicine has also claimed it as a treatment for pain, rheumatism, tension and nervousness, coughs and insanity; scientific evidence of these benefits in humans has not been found, although some similar effects have been demonstrated in mice and toads.[28] The religious ties of lettuce continue into the present day among the Yazidi people of northern Iraq, who have a religious prohibition against eating the plant.[53]
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