We explain what fermentation is, what are the types of fermentation that can be used and the different uses it has.
What is fermentation?
An incomplete oxidation process is called fermentation, which does not require oxygen to take place, and which yields an organic substance as a result. It is a catabolic type process, that is, the transformation of complex molecules into simple molecules and the generation of chemical energy in the form of ATP (Adenos n Triphosphate).
The fermentation consists in a process of glycolysis (breakdown of the glucose molecule) which produces pyruvate (pyruvic acid) and which Since it lacks oxygen as a receptor for the remaining electrons of the NADH (nicotinindendenindependent nicotin) produced, it uses an organic substance that must be reduced for this purpose. reoxidate NADH to NAD +, finally obtaining a derivative of the initial substrate that oxidizes. Depending on said final substance, there will be various types of fermentation.
This process was discovered by the French chemist Louis Pasteur, who described it as Life without air ( La vie sans l air ), since it can be carried out in the absence of oxygen by microorganisms such as bacteria, yeasts, or some metazoans and protists. In this process, then, neither mitochondria nor structures linked to the process of cellular respiration
Compared with the breath of aerobicity, fermentation is not a very efficient method of obtaining energy : they occur only 2 molecules of ATP per molecule of glucose consumed, while breathing, 36 to 38 are obtained.
However, it is carried out by various cells of our body to alleviate the moments of absence of oxygen, as it happens in the muscle cells that ferment glucose when the oxygen intake Oxygen is not enough to continue breathing.
See also: Hydrolysis.
According to the substance obtained at the end of the fermentation process, we can classify it into:
- Alcoholic fermentation Carried out mainly by yeasts, it produces from certain sugars an amount of alcohol ethanol, carbon dioxide and ATP. This is the process used to produce alcoholic beverages.
- Acetic fermentation . Own bacteria of the genus Acetobacter, transforms ethyl alcohol into acetic acid, that is, alcohol in vinegar. It is, however, an aerobic process, so it can occur in wines exposed to the air.
- Lactic fermentation . It consists of a partial oxidation of glucose, carried out by lactic bacteria or by animal muscle cells (when they run out of oxygen to breathe). This process generates ATP but byproducts lactic acid, which produces, when accumulated, the painful sensation of muscle fatigue.
- Butyric Fermentation Discovered by Pasteur, it consists of the conversion of glucoses into butyric acid and gas, the latter gives it a typically unpleasant smell. It is carried out characteristically by the bacteria of the genus Clostridium and requires the presence of lactose.
- Butanediolic Fermentation It is a variant of lactic fermentation, carried out by enterobacteria that release carbon dioxide and generate butanediol, a colorless and viscous alcohol.
- Propionic Fermentation Acetic acid, carbon dioxide and succinic acid are involved in this process, and propionic acid, a corrosive substance with a pungent odor, is obtained from all of them.
Numerous human industries take advantage of fermentation to obtain certain substances . For example, in the food industries of cheese, propionic fermentation processes are carried out, or in the preservation of many types of foodstuffs the presence of lactic acid, which acts as a preservative, due to lactic fermentation.
Something similar occurs with the alcoholic industry, both wines, beers or other types of spirits, which require a manufacturing process involving alcoholic fermentation. On the contrary, if some liquors such as wine are left uncovered for a long time, the added oxygen will start the acetic fermentation and the drink will start to pick up.