Industrial In industry, butyric acid is produced by
hydroformylation from
propene and
syngas, forming
butyraldehyde, which is
oxidised to the final product. This fermentation pathway was discovered by
Louis Pasteur in 1861. Examples of butyrate-producing
species of bacteria: •
Clostridium butyricum •
Clostridium kluyveri •
Clostridium pasteurianum •
Faecalibacterium prausnitzii •
Fusobacterium nucleatum •
Butyrivibrio fibrisolvens •
Eubacterium limosum The pathway starts with the
glycolytic cleavage of
glucose to two
molecules of
pyruvate, as happens in most organisms. Pyruvate is
oxidized into
acetyl coenzyme A catalyzed by
pyruvate:ferredoxin oxidoreductase. Two molecules of
carbon dioxide () and two molecules of
hydrogen () are formed as waste products. Subsequently, is produced 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 Other pathways to butyrate include
succinate reduction and crotonate disproportionation. Several species form
acetone and
n-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 butyrate fermentation, as described above, but, when the
pH drops below 5, they switch into butanol and acetone production 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 • acetoacetyl CoA → butyryl CoA → butyraldehyde → butanol For commercial purposes Clostridium species are used preferably for butyric acid or butanol production. The most common species used for probiotics is the
Clostridium butyricum.
Fermentable fiber sources Highly-fermentable fiber residues, such as those from
resistant starch,
oat bran,
pectin, and
guar are transformed by
colonic bacteria into
short-chain fatty acids (SCFA) including butyrate, producing more SCFA than less fermentable fibers such as
celluloses. One study found that resistant starch consistently produces more butyrate than other types of
dietary fiber. The production of SCFA from fibers in
ruminant animals such as cattle is responsible for the butyrate content of milk and butter.
Fructans are another source of prebiotic soluble dietary fibers which can be digested to produce butyrate. They are often found in the soluble fibers of foods which are high in
sulfur, such as the
allium and
cruciferous vegetables.
Sources of fructans include
wheat (although some wheat strains such as
spelt contain lower amounts),
rye,
barley,
onion,
garlic,
Jerusalem and
globe artichoke,
asparagus,
beetroot,
chicory,
dandelion leaves,
leek,
radicchio, the white part of
spring onion,
broccoli,
brussels sprouts,
cabbage,
fennel, and
prebiotics, such as fructooligosaccharides (
FOS),
oligofructose, and
inulin. Dietary patterns strongly influence colonic butyrate production, as certain foods contain high levels of fermentable fibres that are preferentially metabolized by butyrate-producing bacteria. Resistant starch–rich foods such as cooked-and-cooled potatoes, rice, and legumes substantially increase luminal butyrate concentrations compared with lower-fermentability fibres. Soluble fibres found in oats, barley β-glucans, pectin-rich fruits (apples, citrus), and guar gum similarly enhance microbial butyrate formation. ==Chemical reactions==