View source for Fermentation (biochemistry)

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[[Image:Fermenting.jpg|thumb|right|Fermentation in progress]]

'''Fermentation''' is the process of deriving energy from the [[Redox|oxidation]] of organic compounds, such as carbohydrates, using an [[Endogeny|endogenous]] electron acceptor, which is usually an organic compound.<ref name="Prescott Microbiology">{{cite book |author=Klein, Donald W.; Prescott, Lansing M.; Harley, John |title=Microbiology |publisher=McGraw-Hill |location=New York |year=2005 |pages= |isbn=0-07-255678-1 |url=http://highered.mcgraw-hill.com/sites/0072556781/information_center_view0/}}</ref> This is in contrast to [[cellular respiration]], where electrons are donated to an exogenous electron acceptor, such as oxygen, via an electron transport chain.  Fermentation does not necessarily have to be carried out in an [[anaerobic]] environment. For example, even in the presence of abundant oxygen, [[yeast]] cells greatly prefer fermentation to [[oxidative phosphorylation]], as long as sugars are readily available for consumption.<ref>Dickinson, J. R. (1999). Carbon metabolism. In: The Metabolism and Molecular Physiology of Saccharomyces cerevisiae, ed. J. R. Dickinson and M. Schweizer, Philadelphia, PA: Taylor & Francis.</ref>

Sugars are the most common [[Substrate (biochemistry)|substrate]] of fermentation, and typical examples of fermentation products are [[ethanol]], [[lactic acid]], and [[hydrogen]]. However, more exotic compounds can be produced by fermentation, such as [[butyric acid]] and [[acetone]]. [[Yeast]] carries out [[fermentation (food)|fermentation]] in the production of [[ethanol]] in [[beer]]s, [[wine]]s and other alcoholic drinks, along with the production of large quantities of [[carbon dioxide]]. Fermentation occurs in [[mammal]]ian [[muscle]] during periods of intense exercise where oxygen supply becomes limited, resulting in the creation of [[lactic acid]].<ref name="Voet and Voet, Biochemistry"> Voet and Voet (1995) Biochemistry, 2nd ed., John Wiley & Sons, Inc., New York, NY</ref>

==Energy source in anaerobic conditions==
Fermentation products contain chemical energy (they are not fully
oxidized) but are considered waste products, since they cannot be
metabolized further without the use of oxygen (or other more
highly-oxidized electron acceptors). A consequence is that the
production of [[adenosine triphosphate]] (ATP) by fermentation is less efficient than oxidative phosphorylation, whereby [[pyruvate]] is fully oxidized to carbon dioxide.

* [[Ethanol fermentation]] (performed by [[yeast]] and some types of [[bacterium|bacteria]]) breaks the pyruvate down into ethanol and carbon dioxide. It is important in [[bread]]-making, [[brewing]], and [[wine]]-making.  Usually only one of the products is desired; in bread-making, the alcohol is baked out, and, in alcohol production, the carbon dioxide is released into the atmosphere or used for carbonating the beverage.  When the ferment has a high concentration of [[pectin]], minute quantities of [[methanol]] can be produced.

* [[Lactic acid fermentation]] breaks down the pyruvate into [[lactic acid]]. It occurs in the muscles of animals when they need energy faster than the [[blood]] can supply oxygen. It also occurs in some kinds of [[bacterium|bacteria]] (such as [[lactobacilli]]) and some [[fungi]]. It is this type of bacteria that converts [[lactose]] into lactic acid in [[yogurt]], giving it its sour taste.  These lactic acid bacteria can be classed as homofermentative, where the end product is mostly lactate, or heterofermentative, where some lactate is further metabolized and results in carbon dioxide, acetate or other metabolic products.
* Hydrogen gas is produced in many types of fermentation ([[mixed acid fermentation]], [[butyric acid]] fermentation, [[caproate]] fermentation, [[butanol]] fermentation, [[glyoxylate]] fermentation), as a way to regenerate NAD<sup>+</sup>from NADH. Electrons are transferred to ferredoxin, which in turn is oxidized by hydrogenase, producing H<sub>2</sub>. Hydrogen gas is a substrate for methanogens and sulfate reducers, which keep the concentration of hydrogen sufficiently low to allow the production of such an energy-rich compound.<ref name=Brock>Madigan, Martinko, ''Brock Biology of Microorganisms.</ref>

==History==
{{Unreferenced section|date=September 2008}}
[[France|French]] chemist [[Louis Pasteur]] was the first [[Zymurgy|zymologist]], when, in 1857, he connected yeast to fermentation. Pasteur originally defined fermentation as ''respiration without air''.

Pasteur performed careful research and concluded, ''"I am of the opinion that alcoholic fermentation never occurs without simultaneous organization, development and multiplication of cells.... If asked, in what consists the chemical act whereby the sugar is decomposed ... I am completely ignorant of it."''

German chemist and [[Zymurgy|zymologist]], [[Eduard Buchner]], winner of the 1907 [[Nobel Prize]] in chemistry, later determined that fermentation is actually caused by a yeast secretion that he termed ''[[zymase]]''.

==Etymology==
The term Fermentation is derived from the Latin verb "fevere" which means "to boil".

==See also==
* [[Dark fermentation]]
* [[Fermentation (wine)]]
* [[Fermentation (food)]]
* [[Fermentative hydrogen production]]
* [[Industrial fermentation]]
* [[Fermentation lock]]
* [[Fed-batch]]
* [[Chemostat]]
* [[Ethanol fermentation]]
* [[Photofermentation]]

==References==
{{reflist}}

==External links==
 [http://www2.ufp.pt/~pedros/bq/respi.htm The chemical logic behind fermentation and respiration]


{{Carbohydrate metabolism}}

[[Category:Anaerobic digestion]]
[[Category:Fermented beverages|*]]
[[Category:Metabolism]]
[[Category:Food preservation]]
[[Category:Fermentation]]
[[Category:Microbiology]]
[[Category:Catalysis]]

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