Everything about Butyric Acid totally explained
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Butyric acid (from
Greek βούτυρος =
butter), also known under the systematic name
butanoic acid, is a
carboxylic acid with the structural formula
CH3CH
2CH
2-
COOH. It is found in rancid
butter,
parmesan cheese,
vomit, and
body odor and has an unpleasant
smell and acrid
taste, with a sweetish aftertaste (similar to
ether). Butyric acid can be detected by
mammals with good scent detection abilities such as
dogs at 10
ppb, whereas
humans can detect it in concentrations above 10
ppm.
Butyric acid is a
fatty acid occurring in the form of
esters in animal fats and plant oils. The
glyceride of butyric acid makes up 3% to 4% of butter. When butter goes rancid, butyric acid is liberated from the glyceride by
hydrolysis leading to the unpleasant odor. It is an important member of the fatty acid sub-group called
short chain fatty acids. Butyric acid is a
weak acid with a
pKa of 4.82, similar to
acetic acid which has pKa 4.76. The similar strength of these acids results from their common -CH
2COOH terminal structure. Butyric acid has density 0.96 g/cm
3 and molecular mass 88.1051; thus pure butyric acid is 10.9
molar.
Butyric acid or fermentation butyric acid is also found as a hexyl
ester (hexyl butanoate) in the oil of
Heracleum giganteum (a type of
cow parsnip) and as an octyl ester (octyl butanoate) in
parsnip (
Pastinaca sativa); it has also been noticed in the fluids of the flesh and in perspiration.
It is industrially prepared by the fermentation of
sugar or
starch, brought about by the addition of putrefying
cheese, with
calcium carbonate added to neutralize the acids formed in the process. The butyric fermentation of starch is aided by the direct addition of
Bacillus subtilis. Salts and esters of the acid are called
butanoates.
Butyric acid is used in the preparation of various butanoate esters. Low-molecular-weight esters of butyric acid, such as
methyl butanoate, have mostly pleasant aromas or tastes. As a consequence, they find use as food and perfume additives. They are also used in organic laboratory courses, to teach the
Fisher esterification reaction.
The acid is an oily colorless liquid that freezes at -8
°C; it boils at 164 °C. It is easily soluble in
water,
ethanol, and
ether, and is precipitated out of its aqueous solution by the addition of
calcium chloride.
Potassium dichromate and
sulfuric acid oxidize it to
carbon dioxide and
acetic acid, while alkaline
potassium permanganate oxidizes it to carbon dioxide. The calcium salt, Ca(C
4H
7O
2)
2·H
2O, is less soluble in hot water than in cold.
Butyric acid has a
structural isomer called
isobutyric acid (2-methylpropanoic acid).
Butanoate fermentation
Butanoate is produced as end-product of a fermentation process solely performed by obligate
anaerobic bacteria. Fermented
Kombucha "tea" includes butyric acid as a result of the fermentation. This fermentation pathway was discovered by
Louis Pasteur in
1861. Examples of butanoate-producing
species of bacteria:
The pathway starts with the
glycolytic cleavage of
glucose to two
molecules of
pyruvate, as happens in most organisms. Pyruvate is then
oxidized into
acetyl coenzyme A using a unique mechanism that involves an
enzyme system called
pyruvate-ferredoxin oxidoreductase. Two molecules of
carbon dioxide (CO
2) and two molecules of elemental
hydrogen (H
2) are formed as wastes products from the cell. Then:
ATP is produced, as can be seen, in the last step of the fermentation. Three molecules of ATP are produced for each glucose molecule, a relatively high yield. The balanced equation for this fermentation is:
C6H12O6 → C4H8O2 + 2CO2 + 2H2
Acetone and butanol fermentation
Several species form
acetone and
butanol in an alternative pathway, which starts as butyrate fermentation. Some of these species are:
Clostridium acetobutylicum: the most prominent acetone and butanol producer, used also in industry
Clostridium beijerinckii
Clostridium tetanomorphum
Clostridium aurantibutyricum
These bacteria begin with butanoate fermentation as described above, but, when the pH drops below 5, they switch into butanol and acetone production in order to prevent further lowering of the pH. Two molecules of butanol are formed for each molecule of acetone.
The change in the pathway occurs after acetoacetyl CoA formation. This intermediate then takes two possible pathways:
Acetoacetyl CoA → acetoacetate → acetone, or
Acetoacetyl CoA → butyryl CoA → butanal → butanol.
Butyric acid function/activity
Highly-fermentable fibers like oat bran, pectin, and guar are transformed by colonic bacteria into short chain fatty acids including butyrate.
Butanoate has diverse and, it seems, paradoxical effects on cellular proliferation, apoptosis and differentiation that may be either pro-neoplastic or anti-neoplastic, depending upon factors such as the level of exposure, availability of other metabolic substrate, and the intracellular milieu. Butanoate is thought by some to be protective against colon cancer. However, not all studies support a chemopreventive effect, and the lack of agreement (particularly between in vivo and in vitro studies) on butyrate and colon cancer has been termed the "butyrate paradox." There are many reasons for this discrepant effect, including differences between the in vitro and in vivo environments, the timing of butanoate administration, the amount administered, the source (usually dietary fiber) as a potential confounder, and an interaction with dietary fat. Together, the studies suggest that the chemopreventive benefits of butanoate depend in part on amount, time of exposure with respect to the tumorigenic process, and the type of fat in the diet. Low carbohydrate diets like the Atkins diet are known to reduce the amount of butanoate produced in the colon.
Butyric acid has been associated with the ability to inhibit the function of histone deacetylase enzymes, thereby favouring an acetylated state of histones in the cell. Acetylated histones have a lower affinity for DNA than non-acetylated histones, due to the neutralisation of electrostatic charge interactions. In general, it's thought that transcription factors will be unable to access regions where histones are tightly associated with DNA (ie non-acetylated, for example, heterochromatin). Therefore, it's thought that butyric acid enhances the transcriptional activity at promoters, which are typically silenced/downregulated due to histone deacetylase activity.
This article incorporates information from the 1911 encyclopedia.Further Information
Get more info on 'Butyric Acid'.
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