LETTUCE

Lettuce (Lactuca sativa) is an annual plant of the aster or sunflower family Asteraceae. It is most often grown as a leaf vegetable, but also 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 make oil into a plant grown for its leaves. It spread to the Greeks and Romans, who gave it the name "lactuca", from which the modern "lettuce" ultimately derives. By 50 AD, multiple types were described, and it 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 quickly flowering. 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, and 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.


NUTRITION HEALTH


Depending on the variety, lettuce is a good source of vitamin A 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.
[edit]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 is Listeria 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.
Other bacteria found on lettuce include Aeromonas species, which have not been linked to any outbreaks; Campylobacter species, which cause campylobacteriosis and Yersinia intermedia and Yersinia kristensenii (species of Yersinia), which have been found mainly in lettuce. 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. 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.Salmonella bacteria, including the uncommon Salmonella braenderup type, have also caused outbreaks traced to contaminated lettuce.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.