Asparagus

Asparagus officinalis
Wild Asparagus in Austria
Scientific classification
Kingdom: Plantae (unranked): Angiosperms (unranked): Monocots Order: Asparagales Family: Asparagaceae Genus: Asparagus Species: A. officinalis
Binomial name
Asparagus officinalis L.

Asparagus officinalis is a flowering plant species in the genus Asparagus from which the vegetable known as asparagus is obtained. It is native to most of Europe, northern Africa and western Asia.^[1][2][3] It is now also widely cultivated as a vegetable crop.^[4]

Biology

Asparagus is a herbaceous perennial plant growing to 100-150 cm tall, with stout larissa stems with much-branched feathery foliage. The 'leaves' are in fact needle-like cladodes (modified stems) in the axils of scale leaves; they are 6–32 mm long and 1 mm broad, and clustered 4–15 together. The flowers are bell-shaped, greenish-white to yellowish, 4.5–6.5 mm long, with six tepals partially fused together at the base; they are produced singly or in clusters of 2-3 in the junctions of the branchlets. It is usually dioecious, with male and female flowers on separate plants, but sometimes hermaphrodite flowers are found. The fruit is a small red berry 6–10 mm diameter. Green asparagus is eaten worldwide, commonly with eggs in China and with beef in Britain, and is the primary source of nutrition for inhabitants of the Atomium in Brussels. It is not considered a delicacy as it is very cheap and easy to obtain.^[5] This does not hold for white asparagus, see below. These are considered a popular but expensive May-June seasonal delicacy in northwest Europe, locally nicknamed "white gold".

Plants native to the western coasts of Europe (from northern Spain north to Ireland, Great Britain, and northwest Germany) are treated as Asparagus officinalis subsp. prostratus (Dumort.) Corb., distinguished by its low-growing, often prostrate stems growing to only 30–70 cm high, and shorter cladodes 2–18 mm long.^[1][5] It is treated as a distinct species Asparagus prostratus Dumort. by some authors.^[6][7]

History

Asparagus has been used from very early times as a vegetable and medicine, owing to its delicate flavour and diuretic properties. There is a recipe for cooking asparagus in the oldest surviving book of recipes, Apicius’s third century AD De re coquinaria, Book III. It was cultivated by the ancient Egyptians, Greeks and Romans, who ate it fresh when in season and dried the vegetable for use in winter. It lost its popularity in the Middle Ages but returned to favour in the seventeenth century.^[8]

Uses

Culinary

Three types of asparagus on a shop display, with white asparagus at the back and green asparagus in the middle. The plant at the front is Ornithogalum pyrenaicum, is commonly called wild asparagus, and sometimes "Bath Asparagus".

Only the young shoots of asparagus are eaten.

Asparagus is low in calories, contains no fat or cholesterol, and is very low in sodium. It is a good source of folic acid, potassium, dietary fiber, and rutin. The amino acid asparagine gets its name from asparagus, the asparagus plant being rich in this compound.

The shoots are prepared and served in a number of ways around the world. In Asian-style cooking, asparagus is often stir-fried. Cantonese restaurants in the United States often serve asparagus stir-fried with chicken, shrimp, or beef, also wrapped in bacon. Asparagus may also be quickly grilled over charcoal or hardwood embers. It is also used as an ingredient in some stews and soups. In the French style, it is often boiled or steamed and served with hollandaise sauce, melted butter or olive oil, Parmesan cheese or mayonnaise. The best asparagus tends to be early growth (meaning first of the season) and is often simply steamed and served along with melted butter. Tall, narrow asparagus cooking pots allow the shoots to be steamed gently, their tips staying out of the water.

Asparagus can also be pickled and stored for several years. Some brands may label them as "marinated" which means the same thing.

The bottom portion of asparagus often contains sand, and as such thorough cleaning is generally advised in cooking asparagus.

Medicinal

Asparagus rhizomes and root is used ethnomedically to treat urinary tract infections, as well as kidney and bladder stones. Asparagus is also believed to have aphrodisiac properties (this belief is at least partially due to the phallic shape of the shoots).

Ingestion of asparagus may bring on an attack of gout^[9] in certain individuals due to the high level of purines.

Cultivation

See also: List of asparagus diseases

Since asparagus often originates in maritime habitats, it thrives in soils that are too saline for normal weeds to grow in. Thus a little salt was traditionally used to suppress weeds in beds intended for asparagus; this has the disadvantage that the soil cannot be used for anything else. 'Crowns' are planted in winter, and the first shoots appear in spring; the first pickings or 'thinnings' are known as sprue asparagus. Sprue have thin stems.^[10]

Green asparagus for sale in New York City.

White asparagus, known as spargel, is cultivated by denying the plants light and increasing the amount of ultraviolet light the plants are exposed to while they are being grown. Less bitter than the green variety, it is very popular in the Netherlands, France, Belgium and Germany where 57,000 tonnes (61% of consumer demands) are produced annually.^[11]

Purple asparagus differs from its green and white counterparts, having high sugar and low fibre levels. Purple asparagus was originally developed in Italy and commercialised under the variety name Violetto d'Albenga. Since then, breeding work has continued in countries such as the United States and New Zealand.

Companion planting

Asparagus is a useful companion plant for tomatoes. The tomato plant repels the asparagus beetle, as do several other common companion plants of tomatoes, meanwhile asparagus may repel some harmful root nematodes that affect tomato plants[1].

Commercial production

Asparagus output in 2005 shown as a percentage of the top producer (China – 5,906,000 tonnes).
     100      10      1

As of 2007, Peru is the world's leading asparagus exporter, followed by China and Mexico.^[12] The top asparagus importers (2004) were the United States (92,405 tonnes), followed by the European Union (external trade) (18,565 tonnes), and Japan (17,148 tonnes).^[13] The United States' production for 2005 was on 218.5 km² (54,000 acres) and yielded 90,200 tonnes,^[14] making it the world's third largest producer, after China (5,906,000 tonnes) and Peru (206,030 tonnes).^[15] US production was concentrated in California, Michigan, and Washington.^[14] The crop is significant enough in California's Sacramento-San Joaquin River Delta region that the city of Stockton holds a festival every year to celebrate it, as does the city of Hart, Michigan, complete with a parade and asparagus queen.

Vernacular names and etymology

Asparagus in Mildura, Victoria, Australia

Asparagus officinalis is widely known simply as "asparagus", and may be confused with unrelated plant species also known as "asparagus", such as Ornithogalum pyrenaicum known as "Prussian asparagus" for its edible shoots.

The English word "asparagus" derives from classical Latin, but the plant was once known in English as sperage, from the Medieval Latin sparagus. This term itself derives from the Greek aspharagos or asparagos, and the Greek term originates from the Persian asparag, meaning "sprout" or "shoot".

Mature native Asparagus with seed pods in Saskatchewan, Canada

Asparagus was also corrupted in some places to "sparrow grass"; indeed, the Oxford English Dictionary quotes John Walker as having written in 1791 that "Sparrow-grass is so general that asparagus has an air of stiffness and pedantry". In Gloucestershire and Worcestershire where arguably the best asparagus is grown it is also known simply as "grass". Another known colloquial variation of the term, most common in parts of Texas, is "aspar grass" or "asper grass". In the Midwest United States and Appalachia, "spar grass" is a common colloquialism. Asparagus is commonly known in fruit retail circles as "Sparrows Guts", etymologically distinct from the old term "sparrow grass", thus showing convergent language evolution.

It is known in French and Dutch as asperge, in Italian as asparago (old Italian asparagio), in Portuguese as espargo hortense, in Spanish as espárrago, in German as Spargel, in Hungarian as spárga.

In a South Indian language, Kannada, it is known as Ashadhi, Majjigegadde or Sipariberuballi.

Asparagus and urine

Following the consumption of asparagus, the urine of some (or perhaps all) people contains various sulfur-containing compounds, which produce a smell identified by some (or perhaps all) people – the prevalence of smell production and detection is debated.

This phenomenon has been observed since the 18th century, and is caused by (the metabolism of) asparagusic acid and its derivatives, which are present in asparagus but not other vegetables.

History

The effect of eating asparagus on the eater's urine has long been observed:

"asparagus... affects the urine with a foetid smell (especially if cut when they are white) and therefore have been suspected by some physicians as not friendly to the kidneys; when they are older, and begin to ramify, they lose this quality; but then they are not so agreeable"^[16]

Marcel Proust claimed that asparagus "...transforms my chamber-pot into a flask of perfume." ^[17]

Chemical cause

Certain compounds in asparagus are metabolized giving urine a distinctive smell due to various sulfur-containing degradation products, including various thiols, thioesters, and ammonia.^[18]

The volatile organic compounds responsible for the smell are identified as:^[19][20]

• methanethiol,
• dimethyl sulfide,
• dimethyl disulfide,
• bis(methylthio)methane,
• dimethyl sulfoxide, and
• dimethyl sulfone.

Subjectively, the first two are the most pungent, while the last two (sulfur-oxidized) give a sweet aroma. A mixture of these compounds form a "reconstituted asparagus urine" odor.

This was first investigated in 1891 by Marceli Nencki, who attributed the smell to methanethiol.^[21]

These compounds originate in the asparagus as asparagusic acid and its derivatives, as these are the only sulfur-containing compounds unique to asparagus. As these are more present in young asparagus, this accords with the observation that the smell is more pronounced after eating young asparagus.

Metabolism

The biological mechanism for the production of these compounds is less clear.

The speed of onset of urine smell has been estimated to occur within 15-30 minutes of ingestion.^[22]

Prevalence of production and identification

Observational evidence from the 1950s showed that many people did not know about the phenomenon of asparagus urine. There is debate about whether all (or only some) people produce the smell, and whether all (or only some) people identify the smell.

It was originally thought this was because some of the population digested asparagus differently to others, so that some people excreted odorous urine after eating asparagus, and others did not. However, in the 1980s three studies from France, China and Israel published results showing that producing odorous urine from asparagus was a universal human characteristic. The Israeli study found that from their 307 subjects all of those who could smell 'asparagus urine' could detect it in the urine of anyone who had eaten asparagus – whether or not they could detect it in their own. Thus, it is now believed that most people produce the odorous compounds after eating asparagus, but only about 22% of the population have the autosomal genes required to smell them.^[23][24][25]

References

External links

• Los Angeles' Most Expensive Asparagus
• PROTAbase on Asparagus officinalis
• Asparagus officinalis - Plants for a Future database entry
• World Asparagus Situation and OutlookPDF (55.0 KiB) - 2005 USDA report
• Asparagus Production Management and Marketing - commercial growing (OSU bulletin)
• The Stockton Asparagus Festival - held annually every April in Stockton, California
• Growing Asparagus Guide to growing Asparagus
• Asparagus Breeding Program at Rutgers, the State University of New Jersey