Fermentation is an anaerobic process that aims to produce ATP. Its phases are glycolysis and pyruvate reduction.
In the process of glycolysis, a glucose molecule with six carbons is broken down into two molecules of pyruvate, which have three carbon atoms each. Glycolysis, which occurs in the cytoplasm of all existing cells on the planet, is an anaerobic process, that is, it does not require oxygen to occur.
Glycolysis takes place in a sequence of ten steps, which occur due to the presence of some specific enzymes and form intermediate sugars. The net yield in ATP is two molecules per molecule of glucose , as two molecules of ATP are initially hydrolyzed for the first steps to take place, but four molecules are produced in the end. The equation that summarizes the process is:
Glucose + 2NAD+ + 2ADP + 2Pi → 2 Pyruvate + 2NADH + 2H + + 2ATP + 2H 2 O
→ Pyruvate reduction
Under conditions where oxygen is not present (anaerobic conditions), pyruvate and electrons from NADH remain in the cytosol. Pyruvate can be converted into ethanol and CO 2 , as is the case with yeasts, or it can be converted into lactate, as in muscles. When the anaerobic process results in the formation of lactate, we have lactic fermentation; when the process results in ethanol, we have alcoholic fermentation. These reactions regenerate NAD+ from NADH, a process necessary for glycolysis to continue.
In both lactic acid and alcoholic fermentation, the two electrons from NADH are transferred to the central carbon of pyruvate. However, in alcoholic fermentation, this process is preceded by the release of carbon dioxide. The equations that represent this process are:
Alcoholic fermentation: Glucose + 2ADP + 2Pi → 2 Ethanol + 2CO2 + 2ATP + 2 H 2 O
Lactic fermentation: Glucose + 2ADP + 2Pi → 2 Lactate + 2ATP + 2 H 2 O
→ Use of alcoholic fermentation and lactic fermentation
Alcoholic fermentation is an important and profitable process, as it is used in the manufacture of alcoholic beverages , in the manufacture of bread and even in the production of fuel. Lactic fermentation, in turn, is used in the production of cheese and yogurt