It smells penetratingly like vomit, and criminal figures take advantage of its stench and corrosive effect for attacks. Within our digestive system, however, butyric acid has an important function, and it is also a valuable raw material for medicine and chemistry.
What is butyric acid?
The name butyric acid is the trivial name for butanoic acid. It belongs to the monocarboxylic acids and is the simplest fatty acid of all. Its chemical formula is C4H8O2, so its molecules are each composed of four carbon atoms, eight hydrogen atoms and two oxygen atoms. The liquid, which is colorless at room temperature and somewhat oily, is soluble in water and has a strong irritant effect on the mucous membranes. Its penetrating rancid odor is perceived by humans and animals even in the smallest concentrations. We perceive it as a sign of putrefaction and thus as negative. In nature, butyric acid is formed during the microbial decomposition of organic substances by a process known as butyric acid fermentation. Its melting point of minus 5 degrees Celsius is lower than that of water, and its boiling point is 163 degrees Celsius. Salts and esters of butanoic acid are known in chemistry as butyrates or butanoates.
Function, action and tasks
No healthy intestinal mucosa without butyric acid – this heading can be used to summarize the many mechanisms of action in which this irritating liquid is involved in the human organism. The uppermost cell layer on the inside of our intestines, the so-called intestinal epithelium, is responsible for the processes of mucus secretion and the absorption of food substances from the intestines. For this so important intestinal epithelium, butyric acid and its derivatives are the main energy sources. Only when their level in the intestinal environment is sufficiently high can the metabolism of the intestinal mucosa function optimally. Butyric acid stimulates intestinal motility, protects the intestine and promotes cell growth, but especially the growth of blood vessels in the intestinal wall. In addition, it strengthens the connection between the individual cells in the intestinal wall, thus preventing the intestinal flora from penetrating the epithelium and counteracting the development of inflammatory processes. A theory that the acid even protects against colon cancer is currently being supported by more and more studies.
Formation, occurrence, properties and optimal values
Within the human organism, butyric acid is formed in the intestinal flora, more specifically in the colon. Prebiotic carbohydrates that our stomach cannot break down with its digestive enzymes reach here undigested and are processed by intestinal bacteria (including Faecalibacterium prausnitzii). This process corresponds to the butyric acid fermentation already mentioned, and butyric acid is formed in this process. If it is present in sufficient quantities, the pH value in the intestine shifts into the acidic range. Salmonella and other pathogens have a hard time surviving in this environment, and our intestines stay healthy more easily. If the acid has a positive effect here, it tends to have a negative effect elsewhere: it is found in the mucous membrane of the mouth and in human body sweat, and is partly responsible for the unpleasant odor in both places. When fighting moles, voles and other garden pests, gardeners and farmers in turn make use of precisely this property: The little animals also do not like the stench and take flight. Conversely, it is the typical odor of butyric acid that ticks and other insects benefit from: It enables them to locate their potential “victims”. Incidentally, butanoic acid or its (much more pleasant-smelling) esters are used in the production of medicines, skin-care cosmetics, fragrances and liqueurs. Certain compounds of the acid are required for the production of cellulose butyrate, a particularly weather-resistant and impact-resistant plastic.
Diseases and disorders
If the butyric acid level drops in our intestines, the intestinal mucosa may undergo pathological changes. The risk of developing colon cancer or chronic inflammatory bowel diseases such as Crohn’s disease increases. In patients who already suffer from such diseases, a sometimes significantly reduced level of butyric acid has been detected in the intestinal flora. Our diet has a considerable influence on how much butanoic acid is formed in our intestines. In particular, foods rich in fiber and those containing a lot of starch favor its production and can counteract a drop in the level.As important as butyric acid is for our organism where it belongs, it can be dangerous if we come into contact with it from the outside. Serious health problems can occur here. The greatest danger is when the acid is inhaled or through skin contact, because even the smallest amounts of it have a strong corrosive effect. Prolonged inhalation of its vapors in higher concentrations can irritate the respiratory tract so massively that nausea, vomiting, headaches, dizziness, and even fainting can occur. Violent irritating cough can be a consequence as well as damage to the bronchial tubes and lung tissue. If you are exposed to the vapors unprotected over a longer period of time, there is even a risk of pulmonary edema. Skin contact with butyric acid often leads to moderate irritation similar to an allergic skin reaction. The gases escaping from the acid also irritate the eyes, which begin to burn and water severely as a result. Despite all this, butyric acid is not classified as acutely toxic according to the current hazardous substances regulations. Due to its extremely unpleasant odor, it is already noticeable in a concentration that has no toxicological relevance and can therefore be avoided in good time. Neutralization of butyric acid turns out to be difficult and belongs in the hands of experts.
