Coffea

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This article is about the biology of coffee. For the beverage, see Coffee.
Coffea
File:Coffee Tree.JPG
Coffea arabica trees in Brazil
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Gentianales
Family: Rubiaceae
Subfamily: Ixoroideae
Tribe: Coffeeae[1]
Genus: Coffea
L.
Type species
Coffea arabica
L.[2]
Species

Coffea ambongensis
Coffea anthonyi
Coffea arabica - Arabica Coffee
Coffea benghalensis - Bengal coffee
Coffea boinensis
Coffea bonnieri
Coffea canephora - Robusta coffee
Coffea charrieriana - Cameroonian coffee - caffeine free
Coffea congensis - Congo coffee
Coffea dewevrei - Excelsa coffee
Coffea excelsa - Liberian coffee
Coffea gallienii
Coffea liberica - Liberian coffee
Coffea magnistipula
Coffea mogeneti
Coffea stenophylla - Sierra Leonian coffee

File:Coffea canephora W2 IMG 2430.jpg
Coffea canephora green beans on a tree in Goa, India.

Coffea is a large genus (containing more than 90 species)[3] of flowering plants in the madder family, Rubiaceae. They are shrubs or small trees, native to subtropical Africa and southern Asia. Seeds of several species are the source of the popular beverage coffee. After their outer hull is removed, the seeds are commonly called "beans". Coffee beans are widely cultivated in tropical and sub-tropical countries on plantations, for both local consumption and export to probably every other country in the world. Coffee ranks as one of the world's most valuable and widely traded commodity crops and is an important export of a number of countries.

Botany

File:Detail of Coffea canephora branch and leaves.jpg
Coffea canephora

When grown in the tropics, coffee is a vigorous bush or small tree which usually grow to a height of 3–3.5 m (10–12 feet). Most commonly cultivated coffee species grow best at high elevations. Although they are hardy and capable of withstanding severe pruning, they are nevertheless not very tolerant of sub-freezing temperatures, and so cannot be grown in temperate climate zones. To produce a maximum yield of coffee berries/cherries (800–1400 kg per hectare), the plants need substantial amounts of water and fertilizer. Since they grow best in alkaline soils, calcium carbonate and other lime minerals are sometimes used to reduce acidity in the soil, which can occur due to run off of minerals from the soil in mountainous areas.[4] The caffeine in coffee "beans" is a natural defense: a toxic substance which repels many creatures that would otherwise eat the seeds - as with the nicotine in tobacco leaves.

File:CoffeeBerry.jpg
Coffea berries, Bali

There are several species of Coffee that may be grown for the beans, but Coffea arabica is considered by many to have the best overall flavor and quality.[citation needed] The other species (especially Coffea canephora (var. robusta)) are usually grown on land unsuitable for Coffea arabica. The tree produces red or purple fruits (drupes), which contain two seeds (the "coffee beans", which — despite their name — are not true beans, which are the seeds of the legume family). In about 5-10% of any crop of coffee cherries, the cherry will contain only a single bean, rather than the two usually found. This is called a 'peaberry', which is smaller and rounder than a normal coffee bean. It is often removed from the yield and either sold separately, (as in New Guinea Peaberry) or discarded.

The tree of Coffea arabica will grow fruits after 3 –5 years and will produce for about 50 –60 years (although up to 100 years is possible). The blossom of the coffee tree is similar to jasmine in color and smell. The fruit takes about nine months to ripen. Worldwide, an estimated 15 billion coffee trees are grown on 100,000 km2 (39,000 sq mi) of land.

Coffee is used as a food plant by the larvae of some Lepidoptera (butterfly and moth) species including napoleon jacutinDalcera abrasa, Turnip Moth and some members of the genus Endoclita, including E. damor and E. malabaricus.

There are several pests that affect coffee production, including the coffee borer beetle (Hypothenemus hampei) and the coffee leafminer Leucoptera caffeina.

Shade-grown coffee

Main article: Shade-grown coffee
File:Eth1 coffeelady.jpg
Coffee farmer in Ethiopia.

In its natural environment, coffee most often grows in the shade(Paypa). However, most cultivated coffee is produced on full-sun, monocropping plantations, as are most commercial crops, in order to maximize production per unit of land. This practice is, however, detrimental to the natural environment since the natural habitats which existed prior to the establishment of the plantations are destroyed, and all non-Coffea flora and fauna are suppressed - often with chemical pesticides and herbicides. Shade-grown coffee is favored by conservationists, since it permits a much more natural, complex ecosystem to survive on the land occupied by the plantation. Also, it naturally mulches the soil it grows in, lives twice as long as sun-grown varieties, and depletes less of the soil's resources - hence less fertilizer is needed. In addition, shade-grown coffee is considered by some to be of higher quality than sun-grown varieties, as the cherries produced by the Coffea plants in the shade are not as large as commercial varieties; some believe that this smaller cherry concentrates the flavors of the cherry into the seed (bean) itself.[5] Shade-grown coffee is also associated with environmentally friendly ecosystems that provide a wider variety and number of migratory birds than those of sun-grown coffee farms.[5]

Chemistry of green coffee beans

File:Coffee Immature.jpg
Coffea arabica branch with immature fruit - Brazil

The term “green coffee bean” refers to un-roasted mature or immature coffee beans. These have been processed by wet or dry method for removing the outer pulp and mucilage, and have an intact wax layer on the outer surface. When immature, they are green. When mature, they have a brown to yellow or reddish color, and typically weigh 300 to 330 mg per dried coffee bean. Non-volatile and volatile compounds in green coffee beans, such as caffeine, deter many insects and animals from eating them. Further, both non-volatile and volatile compounds contribute to the flavor of the coffee bean when it is roasted. Non-volatile nitrogenous compounds (including alkaloids, trigonelline, proteins and free amino acids) and carbohydrates are of major importance in producing the full aroma of roasted coffee, and for its biological action.

Non-volatile alkaloids

Caffeine (1,3,7-trimethyl-xanthine) is the alkaloid most present in green and roasted coffee beans. The content of caffeine is between 1% and 2.5% w/w of dry green coffee beans. The content of caffeine does not change during maturation of green coffee beans.[6] Lower concentrations of theophylline, theobromine, paraxanthine, liberine, and methylliberine can be found. The concentration of theophylline, an alkaloid noted for its presence in green tea, is reduced during the roasting process (usually about 15 minutes at 230 °C), whereas the concentration of most other alkaloids are not changed.[7] The solubility of caffeine in water increases with temperature and with the addition of chlorogenic acids, citric acid, tartaric acid, all of which are present in green coffee beans (e.g. 1 g caffeine dissolves in 46 mL of water at room temperature, and 5.5 mL at 80 °C).[8] The xanthine alkaloids are odorless but have a bitter taste in water, which however is masked by organic acids present in green coffee.

Trigonelline (N-methyl-nicotinate) is a derivative of vitamin B6, not as bitter as caffeine. In green coffee beans, the content is between 0.6% (w/w) and 1% (w/w). At roasting temperature (230 °C), 85% of the trigonelline is degraded to nicotinic acid, leaving small amounts of the unchanged molecule in the roasted beans. In green coffee beans, trigonelline is synthesized from nicotinic acid (pyridinium-3-carboxylic acid) by methylation from methionine, a sulfur-containing amino acid.[9] Mutagenic activity of trigonelline has been reported.[10]

Proteins and amino acids

Proteins account for 8% (w/w) to 12% (w/w) of dried green coffee beans. Major part of the proteins are of the of 11-S-storage kind(alpha - component of 32 kDa, beta – component of 22 kDa), most of which are degraded to free amino acids during maturation of green coffee beans. Further, 11-S-storage proteins are degraded to their individual amino acids under roasting temperature and are thus an additional source of bitter components due to generation of Maillard products.[11] High temperature, oxygen concentration and low pH degrade 11-S-storage–proteins of green coffee beans to low molecular weight peptides and amino acids. The degradation is accelerated in the presence of organic acids such as chlorogenic acids and their derivatives. Other proteins include enzymes, such as catalase and polyphenol oxidase, which are important for the maturation of green coffee beans. Mature coffee contains free amino acids (4.0 mg amino acid / g robusta coffee and up to 4 .5 mg amino acid /g arabica coffee). In Coffea arabica, alanine is the amino acid with the highest concentration, i.e. 1.2 mg / g followed by asparagine of 0.66 mg/g, whereas in C. robusta, alanine is present at a concentration of 0.8 mg/g and asparagine at 0.36 mg/g.[12][13] The free hydrophobic amino acids in fresh green coffee beans contribute to the unpleasant taste making it impossible to prepare a beverage with such compounds. In fresh green coffee from Peru, these concentrations have been determined as follows: isoleucine 81 mg /kg, leucine 100 mg/kg, valine 93 mg/kg, tyrosine 81 mg/kg, phenylalanine 133 mg /kg. The concentration of gamma-aminobutyric acid (a neurotransmitter) has been determined between 143 mg/ kg and 703 mg/kg in green coffee beans from Tanzania.[14] Roasted coffee beans do not contain any free amino acids, the amino acids in green coffee beans are degraded under roasting temperature to Maillard products (reaction products between the aldehyde group of sugar and the alpha-amino-group of the amino acids). Further, diketopiperazines, e.g. cyclo(proline-proline), cyclo(proline-leucine), cyclo(proline-isoleucine), are generated from the corresponding amino acids, and are the major source of the bitter taste of roasted coffee.[15] The bitter flavor of diketopiperazines is perceptible at around 20 mg/ 1 liter water. The content of diketopiperazines in espresso is about 20 mg to 30 mg which is responsible for its bitterness.

Carbohydrates

Carbohydrates make up about 50% of the dry weight of green coffee beans. The carbohydrate fraction of green coffee is dominated by polysaccharides, such as arabinogalactan, galactomannan and cellulose, contributing to the tasteless flavor of green coffee. Arabinogalactan makes up to 17% of dry weight of green coffee beans with a molecular weight of 90 kDa to 200 kDa. It is composed of beta-1-3-linked galactan main chain with frequent members of arabinose (pentose) and galactose (hexose) residues at the side chains comprising immunomodulating properties by stimulating the cellular defense system (Th-1 response) of the body. Mature brown to yellow coffee beans contain fewer residues of galactose and arabinose at the side chain of the polysaccharides, making the green coffee bean more resistant to physical breakdown and less soluble in water.[16] The molecular weight of the arabiniogalactan in coffee is higher than in most other plants, improving the cellular defense system of the digestive tract compared to arabinogalactan with lower molecular weight.[17] Free monosaccharides are present in mature brown to yellow-green coffee beans. The free part of monosaccharides contains sucrose (gluco-fructose) up to 9000 mg/ 100g of arabica green coffee bean, a lower amount in robustas, i.e. 4500 mg/100g. In arabica green coffee beans the content of free glucose was 30 mg to 38 mg / 100 g, free fructose 23 mg to 30 mg/ 100 g; free galactose 35 mg/ 100g and mannitol 50 mg/100g dried coffee beans, respectively. Mannitol is a powerful scavenger for hydroxyl radicals, which are generated during the peroxidation of lipids in biological membranes.[18]

Lipids

The lipids found in green coffee include: linoleic acid, palmitic acid, oleic acid, stearic acid, arachidic acid, diterpenes, triglycerides, unsaturated long-chain fatty acids, esters and amides. The total content of lipids in dried green coffee is between 11.7 g and 14 g / 100 g.[19] Lipids are present on the surface and in the interior matrix of green coffee beans. On the surface they include derivatives of carboxylic acid-5-hydroxytryptamides with an amide bond to fatty acids (unsaturated C6 to C24) making up to 3% (w/w) of total lipid content or 1200 to 1400 microgram / g dried green coffee bean. Such compounds form a wax cover on the surface of the coffee bean (200 mg to 300 mg lipids / 100 g dried green coffee beans) protecting the interior matrix against oxidation and insects. Further, such molecules have anti-oxidative activity due to their chemical structure.[20] Lipids of the interior tissue are triglycerides, linoleic acid (46% of total free lipids), palmitic acid (30% to 35% of total free lipids), and esters. Arabica have a higher content of lipids (13,5 g to 17,4 g lipids/100 g dried green coffee beans) than robustas (9,8 g to 10,7 g lipids / 100 g dried green coffee beans). The content of diterpenes is about 20% of the lipid fraction. The diterpenes found in green coffee include cafestol, kahweol, 16-O-methyl-kafestol, cafestal, kahweal. Diterpenes are known for their in-vitro protection of liver tissue against chemical oxidation.[21] In coffee oil from green coffee beans the diterpenes are esterified with saturated long chain fatty acids.

Non-volatine chlorogenic acids

Chlorogenic acids belong to a group of compounds known as polyphenols, which are antioxidants. The content of chlorogenic acid in dried green coffee beans of robusta is 65 mg/g and of arabica 140 mg/g, depending on the timing of harvesting. At roasting temperature, more than 70% of chlorogenic acids are destroyed, leaving a residue of less than 30 mg/g in the roasted coffee bean. In contrast to green coffee, green tea contains an average of 85 mg/g polyphenols. These chlorogenic acids could be a valuable inexpensive source of antioxidants. Chlorogenic acids are homologous compounds comprising caffeic acid, ferulic acid and 3,4 dimethoxycinnamic acid which are connected by an ester-bond to the hydroxyl groups of quinic acid (1alpha, 3R, 4alpha, 5R-tetrahydroxy-cyclohexane carboxylic acid)[22] The anti-oxidation capacity of chlorogenic acid is more potent than of ascorbic acid (vitamin C) or mannitol, which is a selective hydroxy-radical scavenger.[23] Chlorogenic acids have a bitter taste in low concentrations such as 50 mg/L water. At higher concentrations of 1g/L water they have a sour taste. Chlorogenic acids increase the solubility of caffeine and are important modulators of taste.

Volatile compounds

Volatile compounds of green coffee beans include short chain fatty acids, aldehydes, and nitrogen containing aromatic molecules, such as derivatives of pyrazines green-herbeaceous-earthy odor. Briefly, such volatile compounds are responsible for the unpleasant odor and taste of green coffee being capable of causing nausea and vomiting upon inhaling of the odor of ground green coffee beans or ingestion of a beverage made by pulverised green coffee beans. Due to this nauseating odor, green coffee beans have never been used by themselves for the preparation of a refreshing beverage; such a beverage would cause vomiting, although green coffee beans contain the same amount of caffeine as roasted coffee. When green coffee beans are roasted, other molecules with the typical pleasant aroma of coffee are generated, which are not present in fresh green coffee. Some have tried to neutralise or transform the nauseating odor-molecules of green coffee beans, producing an innovative flavor by fermentation of the intact mature brown to yellow coffee bean similar to the wet processing of the mature coffee fruit.[24] However, fermented green coffee beans must be further roasted in order to obtain an organoleptic accepted beverage based on coffee. During roasting, the major part of the unpleasant tasting volatile compounds are neutralised. Unfortunately, other important molecules such as antioxidants and vitamins present in green coffee are destroyed. Volatile compounds with nauseating odor for humans have been identified, including acetic acid (pungent, unpleasant odor); propionic acid (odor of sour milk, or butter); butanoic acid (odor of rancid butter, present in green coffee with 2 mg/100 g coffee beans); pentanoic acid (unpleasant fruity flavor, present in green coffee at 40 mg/100 g in coffee beans); hexanoic acid (fatty-rancid odor), heptanoic acid (fatty odor); octanoic acid (repulsive oily rancid odor); nonanoic acid (mild nut-like fatty odor); decanoic acid (sour repulsive odor); and derivatives of such fatty acids; 3-methyl-valeric acid (sour, green-herbaceous, unpleasant odor); acetaldehyde (pungent-nauseating odor, even when highly diluted; present in dried green coffee beans at concentrations of about 5 mg/1 kg); propanal (choking effect on respiratory system, penetrating-nauseating), butanal (nauseating effect; present in dried green coffee beans at 2 to 7 mg/1 kg); pentanal or valerianic aldehyde (very repulsive nauseating effect).[25]

Health properties

Extracts of green coffee have been shown to improve vasoactivity (the ability of the blood vessels to contract or expand freely) in humans.[26]

New coffee species

Recently, two new species of coffee plants have been discovered in Cameroon: Coffea charrieriana and Coffea anthonyi. These species could introduce two new features to cultivated coffee plants: 1) beans without caffeine and 2) self-pollination. By crossing the new species with other known coffees (e.g., C. arabica and C. robusta), new coffee hybrids might allow these new improvements at regular coffee plantations (e.g. in Kenya, since C. arabica and C. robusta are accustomed to these growing conditions).[27]. In 2008 and 2009, researchers from the Royal Botanic Gardens, Kew named seven species of Coffea from the mountains of northern Madagascar, including C. ambongensis, C. boinensis, C. labatii, C. pterocarpa, C. bissetiae, and C. namorokensis.[28]

Other uses

While the beans are the most frequently used part of the plant, the leaves and the berries find occasional use in making herbal tea; see coffee tea. The berries are also edible.[29]

See also

References

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External links

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  1. ↑ "Genus Coffea". Taxonomy. UniProt. Retrieved 2010-02-13. 
  2. ↑ "Coffea L". TROPICOS. Missouri Botanical Garden. Retrieved 2010-02-13. 
  3. ↑ 337_346.pdf
  4. ↑ Significance of Lime Application in Coffee Plantations INeedCoffee. (Accessed 23 July 2006)
  5. ↑ 5.0 5.1 "Why Shade Grown Coffee is Important". Grounds for Change. 
  6. ↑ CLIFFORD, MN, and KAZI, M, 1987, The influence of coffee bean maturity on the content of chlorogenic acids, caffeine, and trigonelline, Food Chemistry, Vol 26, p 59-69
  7. ↑ WEIDNER, M, and MAIER, HG; 1999, Seltene Purinalkaloide in Roestkaffee, Lebensmittelchemie, Vol 53, 3, p.58
  8. ↑ The Merck Index, 13th Edition
  9. ↑ POISSON, J, 1979, Aspects chimiques et biologiquesde la composition du café vert; 8th International Colloquium Chemicum Coffee, Abidjan, 28. Nov to 3. December 1988, published by ASIC 1979, p 33-37; http://www.asic-cafe.org
  10. ↑ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  11. ↑ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  12. ↑ ARNOLD, U., LUDWIG, E., KÜHN, R., MÖSCHWITZER, U., 1994, Analysis of free amino acids in green coffee beans; Z. Lebensm Unters Forsch, Vol 199, p 22-25
  13. ↑ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  14. ↑ TEUTSCH, IA, 2004, Einfluss der Rohkaffeeverarbeitung auf Aromastoffveränderungen in gerösteten Kaffeebohnen sowie im Kaffeebetränk, PhD Thesis, Department of Chemistry, Technical University Munich, Germany; www.deposit.ddb.de/cgi-bin/dokserv?idn=97339305x& dok_var=d1&dok_ext=pdf&filename=97339305x.pdf
  15. ↑ GINZ, M, 2001, Bittere Diketopiperazine und chlorogensäurederivate in Roestkaffee, PhD-thesis, Technical University Carolo-Wilhelminia, Brunswig, Germany, www.digibib.tu-bs.de/?docid=00001257 - 17k
  16. ↑ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  17. ↑ GOTODA, N, IWAI, K, Arabinogalactan isolated from coffee beans indicates immunomodulating properties, p. 116-120; In: Association for Science and Information on Coffee, (ASIC) 21st International Conference on Coffee Science, 11 – 15 September 2006, Montpellier, France
  18. ↑ TRESSEL, R, HOLZER, M and KAMPERSCHROER, H, 1983, Bildung von Aromastoffenin Roestkaffee in Abhaengigkeit vom Gehalt an freien Aminosaeren und reduzierenden Zuckern; 10th International Colloquium Chemicum Coffee, Salvador, Bahia 11 October to 14 Oct; ASIC publication 1983, p279-292
  19. ↑ ROFFI, J, CORTE DOS SANTOS, A, MEXIA, JT, BUSSON, F, and MIAGROT, M, 1973, Café verts et torrefiesde l Angola. Etude chimique, 5th International Colloquium Chemicum Coffee, Lisboa, 14 June to 19 June 1971; published by ASIC 1973, pp 179-200
  20. ↑ Clifford MN (1985). "Chemical and physical aspects of green coffee and coffee products". In Clifford MN, Wilson KC. Coffee: botany, biochemistry, and production of beans and beverage. London: Croom Helm AVI. pp. 305–74. ISBN 0-7099-0787-7. 
  21. ↑ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  22. ↑ CLIFFORD, M.N, 2006, Chlorogenic acids – their characterisation, transformation during roasting, and potential dietary significance, In: Association for Science and Information on Coffee, (ASIC) 21st International Conference on Coffee Science, 11 – 15 September 2006, Montpellier, France, p 36-49
  23. ↑ MORISHITA, H., KIDO, R., 1995; Anti-oxydant activities of chlorogenic acid; 16th international colloqu. Chem. Coffee, Kyoto 9-14, April 1995, ASIC-1995
  24. ↑ US patent application No 20070190207; Method of processing green coffee beans, http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.html&r=1&f=G&l=50&s1=%2220070190207%22.PGNR.&OS=DN/20070190207&RS=DN/20070190207
  25. ↑ Bessière-Thomas, Yvonne; Ivon Flament (2002). Coffee flavor chemistry. Chichester: John Wiley & Sons. ISBN 0-471-72038-0. 
  26. ↑ OCHIAL, R, JOKURA, H, et al., Green coffee bean extract improves human vasoactivity, Association for Science and Information on Coffee, p731–736; ASIC – 21st International Conference on Coffee Science, 11–15 September 2006, Montpellier, France
  27. ↑ Science Connection 22 (July 2008)
  28. ↑ "Seven species of wild coffee amongst Kew's haul of new discoveries" Royal Botanic Gardens, Kew, 22 December 2009. [1]
  29. ↑ Ever Eat A Coffee Cherry?
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