Fermentation theory

Last updated August 19, 2022

In biochemistry, fermentation theory refers to the historical study of models of natural fermentation processes, especially alcoholic and lactic acid fermentation. Notable contributors to the theory include Justus Von Liebig and Louis Pasteur, the latter of whom developed a purely microbial basis for the fermentation process based on his experiments. Pasteur's work on fermentation later led to his development of the germ theory of disease, which put the concept of spontaneous generation to rest.^[1] Although the fermentation process had been used extensively throughout history prior to the origin of Pasteur's prevailing theories, the underlying biological and chemical processes were not fully understood. In the contemporary, fermentation is used in the production of various alcoholic beverages, foodstuffs, and medications.^[2]^[3]

Overview of fermentation

Fermentation is the anaerobic metabolic process that converts sugar into acids, gases, or alcohols in oxygen starved environments. Yeast and many other microbes commonly use fermentation to carry out anaerobic respiration necessary for survival. Even the human body carries out fermentation processes from time to time, such as during long-distance running; lactic acid will build up in muscles over the course of long-term exertion. Within the human body, lactic acid is the by-product of ATP-producing fermentation, which produces energy so the body can continue to exercise in situations where oxygen intake cannot be processed fast enough. Although fermentation yields less ATP than aerobic respiration, it can occur at a much higher rate. Fermentation has been used by humans consciously since around 5000 BCE, evidenced by jars recovered in the Iran Zagros Mountains area containing remnants of microbes similar those present in the wine-making process.

History

Prior to Pasteur's research on fermentation, there existed some preliminary competing notions of it. One scientist who had a substantial degree of influence on the theory of fermentation was Justus von Liebig. Liebig believed that fermentation was largely a process of decomposition as a consequence of the exposure of yeast to air and water.^[4] This theory was corroborated by Liebig's observation that other decomposing matter, such as rotten plant and animal parts, interacted with sugar in a similar manner as yeast. That is, the decomposition of albuminous matter (i.e. water-soluble proteins) caused sugar to transform to alcohol.^[4]^[5] Liebig held this view until his death in 1873.^[4] A different theory was supported by Charles Cagniard de la Tour and cell theorist Theodor Schwann, who claimed that alcoholic fermentation depended on the biological processes carried out by brewer's yeast.^[6]^[5]

Louis Pasteur's interest in fermentation began when he noticed some remarkable properties of amyl alcohol —a by-product of lactic acid and alcohol fermentation—during his biochemical studies. In particular, Pasteur noted its ability to “rotate the plane of polarized light”, and its “unsymmetric arrangement of atoms."^[4] These behaviors were characteristic of organic compounds Pasteur had previously examined, but also presented a hurdle to his own research about a "law of hemihedral correlation".^[6]^[7] Pasteur had previously been attempting to derive connections between substances' chemical structures and external shape, and the optically active amyl alcohol did not follow his expectations according to the proposed 'law'.^[6] Pasteur sought a reason for why there happened to be this exception, and why such a chemical compound was generated during the fermentation process in the first place.^[6] In a series of lectures later in 1860, Pasteur attempted to link optical activity and molecular asymmetry to organic origins of substances, asserting that no chemical processes were capable of converting symmetric substances (inorganic) into asymmetric ones (organic).^[6] Hence, the amyl alcohol observation provided some of the first motivations for an biological explanation of fermentation.

In 1856, Pasteur was able to observe the microbes responsible for alcoholic fermentation under a microscope, as a professor of science in the University of Lille.^[4]^[6] According to a legend originating in the 1900 biography of Pasteur, one of his chemistry students—an owner of a beetroot alcohol factory in Lille—sought aid from him after an unsuccessful year of brewing.^[6] Pasteur performed experiments at the factory in observation of the fermentation process, noticing that yeast globules became elongated after lactic acid was formed, but round and full when alcohol was fermenting correctly.^[6]

In a different observation, Pasteur inspected particles originating on grapevines under the microscope and revealed the presence of living cells. Leaving these cells immersed in grape juice resulted in active alcoholic fermentation. This observation provided evidence for ending the distinction between ‘artificial’ fermentation in wine and ‘true’ fermentation in yeast products.^[4] The previous incorrect distinction had stemmed in part from the fact that yeast had to be added to beer wort in order to provoke desired alcoholic fermentation, while the fermenting catalysts for wine occurred naturally on grapevines; the fermentation of wine had been viewed as 'artificial' since it did not require additional catalyst, but the natural catalyst had been present on the grapevine itself.^[8] These observations provided Pasteur with a working hypothesis for future experiments.^[6]^[7]

One of the chemical processes that Pasteur studied was the fermentation of sugar into lactic acid, as occurs in the souring of milk. In an 1857 experiment, Pasteur was able to isolate microorganisms present in lactic acid ferment after the chemical process had taken place.^[9] Pasteur then cultivated the microorganisms in a culture with his laboratory. He was then able to accelerate the lactic acid fermentation process in fresh milk by administering the cultivated sample to it.^[7] This was an important step in proving his hypothesis that lactic acid fermentation was catalyzed by microorganisms.^[7]^[9]

Pasteur also experimented with the mechanisms of brewer's yeast in the absence of organic nitrogen.^[6] By adding pure brewer's yeast to a solution of cane sugar, ammonium salt, and yeast ash, Pasteur was able to observe the alcoholic fermentation process with all of its usual byproducts: glycerin, succinic acid, and small amounts of cellulose and fatty matters.^[6] However, if any of the ingredients were removed from the solution, no fermentation would occur. To Pasteur, this was proof that yeast required the nitrogen, minerals, and carbon from the medium for its metabolic processes, releasing carbonic acid and ethyl alcohol as byproducts.^[5]^[6] This also disproved Liebig's theory, since there was no albuminous matter present in the medium; the decomposition of the yeast was not the driving force for the observed fermentation.^[5]^[6]

Pasteur on spontaneous generation

Before the 1860s and 1870s—when Pasteur published his work on this theory—it was believed that microorganisms and even some small animals such as frogs would spontaneously generate. Spontaneous generation was historically explained in a variety of ways. Aristotle, an ancient Greek philosopher, theorized that creatures appeared out of certain concoctions of earthly elements, such as clay or mud mixing with water and sunlight.^[10] Later on, Felix Pouchet argued for the existence of 'plastic forces' within plant and animal debris capable of spontaneously generating eggs, and new organisms were born from these eggs.^[5]^[6] On top of this, a common piece of evidence that seemed to corroborate the theory was the appearance of maggots on raw meat after it was left exposed to open air.

In the 1860s and 1870s, Pasteur's interest in spontaneous generation led him to criticize Pouchet's theories and conduct experiments of his own.^[6] In his first experiment, he took boiled sugared yeast-water and sealed it in an airtight contraption. Feeding hot, sterile air into the mixture left it unaltered, while introducing atmospheric dust resulted in microbes and mold appearing within the mixture.^[5]^[6] This result was also strengthened by the fact that Pasteur used asbestos, a form of totally inorganic matter, to carry the atmospheric dust. In a second experiment, Pasteur used the same flasks and sugar-yeast mixture, but left it idle in 'swan-neck' flasks instead of introducing any extraneous matter. Some flasks were kept open to the common air as the control group, and these exhibited mold and microbial growths within a day or two. When the swan-neck flasks failed to show these same microbial growths, Pasteur concluded that the structure of the necks blocked the passage of atmospheric dust into the solution.^[5]^[6] From the two experiments, Pasteur concluded that the atmospheric dust carried germs responsible for the 'spontaneous generation' in his broths.^[6] Thus, Pasteur's work provided proof that the emergent growth of bacteria in nutrient broths is caused by biogenesis rather than some form of spontaneous generation.

Applications

Today, the process of fermentation is used for a multitude of everyday applications including medication, beverages and food. Currently, companies like Genencor International uses the production of enzymes involved in fermentation to build a revenue of over $400 million a year.^[3] Many medications such as antibiotics are produced by the fermentation process. An example is the important drug cortisone, which can be prepared by the fermentation of a plant steroid known as diosgenin.

The enzymes used in the reaction are provided by the mold Rhizopus nigricans.^{[ citation needed ]} Just as it is commonly known, alcohol of all types and brands are also produced by way of fermentation and distillation. Moonshine is a classic example of how this is carried out. Finally, foods such as yogurt are made by fermentation processes as well. Yogurt is a fermented milk product that contains the characteristic bacterial cultures Lactobacillus bulgaricus and Streptococcus thermopiles.^[11]

Related Research Articles

Louis Pasteur was a French chemist and microbiologist renowned for his discoveries of the principles of vaccination, microbial fermentation, and pasteurization. His research in chemistry led to remarkable breakthroughs in the understanding of the causes and preventions of diseases, which laid down the foundations of hygiene, public health and much of modern medicine. His works are credited to saving millions of lives through the developments of vaccines for rabies and anthrax. He is regarded as one of the founders of modern bacteriology and has been honored as the "father of bacteriology" and as the "father of microbiology".

Lactic acid fermentation Metabolic process

Lactic acid fermentation is a metabolic process by which glucose or other six-carbon sugars are converted into cellular energy and the metabolite lactate, which is lactic acid in solution. It is an anaerobic fermentation reaction that occurs in some bacteria and animal cells, such as muscle cells.

Zymology, also known as zymurgy, is an applied science that studies the biochemical process of fermentation and its practical uses. Common topics include the selection of fermenting yeast and bacteria species and their use in brewing, wine making, fermenting milk, and the making of other fermented foods.

Winemaking or vinification is the production of wine, starting with the selection of the fruit, its fermentation into alcohol, and the bottling of the finished liquid. The history of wine-making stretches over millennia. The science of wine and winemaking is known as oenology. A winemaker may also be called a vintner. The growing of grapes is viticulture and there are many varieties of grapes.

Theodor Schwann was a German physician and physiologist. His most significant contribution to biology is considered to be the extension of cell theory to animals. Other contributions include the discovery of Schwann cells in the peripheral nervous system, the discovery and study of pepsin, the discovery of the organic nature of yeast, and the invention of the term "metabolism".

Malolactic conversion is a process in winemaking in which tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid. Malolactic fermentation is most often performed as a secondary fermentation shortly after the end of the primary fermentation, but can sometimes run concurrently with it. The process is standard for most red wine production and common for some white grape varieties such as Chardonnay, where it can impart a "buttery" flavor from diacetyl, a byproduct of the reaction.

Ethanol fermentation, also called alcoholic fermentation, is a biological process which converts sugars such as glucose, fructose, and sucrose into cellular energy, producing ethanol and carbon dioxide as by-products. Because yeasts perform this conversion in the absence of oxygen, alcoholic fermentation is considered an anaerobic process. It also takes place in some species of fish where it provides energy when oxygen is scarce.

Tej is a honey wine, like mead, that is brewed and consumed in Ethiopia and Eritrea. It has an alcohol content generally ranging from 7 to 11%. It is often home processed and consists of three main ingredients; honey, water and a medicinal shrub called Rhamnus prinoides [gesho]. Tej is also available commercially to buy in many different types. It is generally consumed during social events such as festivals or weddings, and religious events like Ethiopian New Year [Enkutatash]. Consequently, Tej forms an important part of Ethiopian society and culture and is considered the national drink of Ethiopia.

Industrial fermentation is the intentional use of fermentation in manufacturing products useful to humans. In addition to the mass production of fermented foods and drinks, industrial fermentation has widespread applications in chemical industry. Commodity chemicals, such as acetic acid, citric acid, and ethanol are made by fermentation. Moreover, nearly all commercially produced industrial enzymes, such as lipase, invertase and rennet, are made by fermentation with genetically modified microbes. In some cases, production of biomass itself is the objective, as is the case for single-cell proteins, baker's yeast, and starter cultures for lactic acid bacteria used in cheesemaking.

Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food production, it may more broadly refer to any process in which the activity of microorganisms brings about a desirable change to a foodstuff or beverage. The science of fermentation is known as zymology.

In food processing, fermentation is the conversion of carbohydrates to alcohol or organic acids using microorganisms—yeasts or bacteria—under anaerobic (oxygen-free) conditions. Fermentation usually implies that the action of microorganisms is desired. The science of fermentation is known as zymology or zymurgy.

The process of fermentation in winemaking turns grape juice into an alcoholic beverage. During fermentation, yeasts transform sugars present in the juice into ethanol and carbon dioxide. In winemaking, the temperature and speed of fermentation are important considerations as well as the levels of oxygen present in the must at the start of the fermentation. The risk of stuck fermentation and the development of several wine faults can also occur during this stage, which can last anywhere from 5 to 14 days for primary fermentation and potentially another 5 to 10 days for a secondary fermentation. Fermentation may be done in stainless steel tanks, which is common with many white wines like Riesling, in an open wooden vat, inside a wine barrel and inside the wine bottle itself as in the production of many sparkling wines.

Cider is an alcoholic beverage made from the fermented juice of apples. Cider is widely available in the United Kingdom and the Republic of Ireland. The UK has the world's highest per capita consumption, as well as the largest cider-producing companies. Ciders from the South West of England are generally stronger. Cider is also popular in many Commonwealth countries, such as India, Canada, Australia, and New Zealand. As well as the UK and its former colonies, cider is popular in Portugal, France, northern Italy, and northern Spain. Central Europe also has its own types of cider with Rhineland-Palatinate and Hesse producing a particularly tart version known as Apfelwein. In the U.S., varieties of fermented cider are often called hard cider to distinguish alcoholic cider from non-alcoholic apple cider or "sweet cider", also made from apples. In Canada, cider cannot contain less than 2.5% or over 13% absolute alcohol by volume.

This glossary of winemaking terms lists some of terms and definitions involved in making wine, fruit wine, and mead.

Liebig–Pasteur dispute is the dispute between Justus von Liebig and Louis Pasteur on the processes and causes of fermentation.

Qū, qú, qūniè, jiǔqū, or jiǔmǔ is a type of East Asian dried fermentation starter grown on a solid medium and used in the production of traditional Chinese alcoholic beverages. The Chinese character 曲/麹 is romanised as qū in pinyin, chhu or chu in other transcription systems. The literal translation of jiǔqū is "liquor ferment", although "liquor mold" or "liquor starter" are adequate descriptions.

Microbial food cultures are live bacteria, yeasts or moulds used in food production. Microbial food cultures carry out the fermentation process in foodstuffs. Used by humans since the Neolithic period fermentation helps to preserve perishable foods and to improve their nutritional and organoleptic qualities. As of 1995, fermented food represented between one quarter and one third of food consumed in Central Europe. More than 260 different species of microbial food culture are identified and described for their beneficial use in fermented food products globally, showing the importance of their use.

Symbiotic fermentation is a form of fermentation in which multiple organisms interact in symbiosis in order to produce the desired product. For example, a yeast may produce ethanol, which is then consumed by an acetic acid bacterium. Described early on as the fermentation of sugars following saccharification in a mixed fermentation process.

Industrial microbiology is a branch of biotechnology that applies microbial sciences to create industrial products in mass quantities, often using microbial cell factories. There are multiple ways to manipulate a microorganism in order to increase maximum product yields. Introduction of mutations into an organism may be accomplished by introducing them to mutagens. Another way to increase production is by gene amplification, this is done by the use of plasmids, and vectors. The plasmids and/ or vectors are used to incorporate multiple copies of a specific gene that would allow more enzymes to be produced that eventually cause more product yield. The manipulation of organisms in order to yield a specific product has many applications to the real world like the production of some antibiotics, vitamins, enzymes, amino acids, solvents, alcohol and daily products. Microorganisms play a big role in the industry, with multiple ways to be used. Medicinally, microbes can be used for creating antibiotics in order to treat infection. Microbes can also be used for the food industry as well. Microbes are very useful in creating some of the mass produced products that are consumed by people. The chemical industry also uses microorganisms in order to synthesize amino acids and organic solvents. Microbes can also be used in an agricultural application for use as a biopesticide instead of using dangerous chemicals and or inoculants to help plant proliferation.

Bokashi is a process that converts food waste and similar organic matter into a soil amendment which adds nutrients and improves soil texture. It differs from traditional composting methods in several respects. The most important are:

References

↑ Pasteur, Louis. "Physiological Theory of Fermentation". Fordham University. Retrieved March 13, 2014.
↑ Fiachson, Refr. "Fermentation in Theory and Practice". Viking Food Guy. Retrieved March 13, 2014.
1 2 Slonczewski, Joan (2009). Microbiology: An Evolving Science 2nd edition. New York: W.W. Norton.
1 2 3 4 5 6 Conant, James Bryant ; Nash, Leonard K. ; Roller, Duane ; Roller, Duane H.D.: Harvard Case Histories in Experimental Science. Volume II. Cambridge, Mass. ISBN 978-0-674-59871-3. OCLC 979880864.
1 2 3 4 5 6 7 Ben-Menahem, Ari. (2009). Historical encyclopedia of natural and mathematical sciences. Berlin: Springer. ISBN 978-3-540-68832-7. OCLC 318545341.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Geison, Gerald L., 1943- (14 July 2014). The private science of Louis Pasteur. Princeton, New Jersey. ISBN 978-1-4008-6408-9. OCLC 889252696.{{cite book}}: CS1 maint: multiple names: authors list (link)
1 2 3 4 Dubos, René J. (René Jules), 1901-1982. (1998). Pasteur and modern science. Brock, Thomas D. Washington, D.C.: ASM Press. ISBN 1-55581-144-2. OCLC 39538952.{{cite book}}: CS1 maint: multiple names: authors list (link)
↑ Tyndall, John (1892). Essays on the floating-matter of the air, in relation to putrefaction and infection. New York: D. Appleton.
1 2 "Louis Pasteur | Lemelson-MIT Program". lemelson.mit.edu. Retrieved 2020-02-16.
↑ Lehoux, Daryn, 1968- (19 November 2017). Creatures born of mud and slime : the wonder and complexity of spontaneous generation. Baltimore. ISBN 978-1-4214-2382-1. OCLC 1011094577.{{cite book}}: CS1 maint: multiple names: authors list (link)
↑ "Milk Facts". Yogurt Production. Retrieved March 30, 2014.

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[1] Pasteur, Louis. "Physiological Theory of Fermentation". Fordham University. Retrieved March 13, 2014.

[Viking-2] Fiachson, Refr. "Fermentation in Theory and Practice". Viking Food Guy. Retrieved March 13, 2014.

[evolving_science-3] 1 2 Slonczewski, Joan (2009). Microbiology: An Evolving Science 2nd edition. New York: W.W. Norton.

[:0-4] 1 2 3 4 5 6 Conant, James Bryant ; Nash, Leonard K. ; Roller, Duane ; Roller, Duane H.D.: Harvard Case Histories in Experimental Science. Volume II. Cambridge, Mass. ISBN 978-0-674-59871-3. OCLC 979880864.

[:3-5] 1 2 3 4 5 6 7 Ben-Menahem, Ari. (2009). Historical encyclopedia of natural and mathematical sciences. Berlin: Springer. ISBN 978-3-540-68832-7. OCLC 318545341.

[:4-6] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Geison, Gerald L., 1943- (14 July 2014). The private science of Louis Pasteur. Princeton, New Jersey. ISBN 978-1-4008-6408-9. OCLC 889252696.{{cite book}}: CS1 maint: multiple names: authors list (link)

[:1-7] 1 2 3 4 Dubos, René J. (René Jules), 1901-1982. (1998). Pasteur and modern science. Brock, Thomas D. Washington, D.C.: ASM Press. ISBN 1-55581-144-2. OCLC 39538952.{{cite book}}: CS1 maint: multiple names: authors list (link)

[8] Tyndall, John (1892). Essays on the floating-matter of the air, in relation to putrefaction and infection. New York: D. Appleton.

[:2-9] 1 2 "Louis Pasteur | Lemelson-MIT Program". lemelson.mit.edu. Retrieved 2020-02-16.

[10] Lehoux, Daryn, 1968- (19 November 2017). Creatures born of mud and slime : the wonder and complexity of spontaneous generation. Baltimore. ISBN 978-1-4214-2382-1. OCLC 1011094577.{{cite book}}: CS1 maint: multiple names: authors list (link)

[11] "Milk Facts". Yogurt Production. Retrieved March 30, 2014.

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