The course of lactic acid fermentation simply explained:
For the purpose of their own energy metabolism, lactic acid bacteria break down carbohydrates into lactic acid. Meanwhile, the universal energy source is created adenosine triphosphate (ATP). All this is anaerobic, therefore without consumption of oxygen. Lactic acid bacteria do not require oxygen for their metabolism, but can easily survive in an oxygenated environment.
Just like the alcoholic fermentation is also the Lactic acid fermentation since the Neolithic, at least in terms of their practical application known. Cheese, yogurt, quark, butter, buttermilk, sour cream, cream and many more Dairy products arise only with the so-called thick laying, the precipitation of the milk protein casein, which make lactic acid bacteria possible.
Also at the preservation from food, and lactic acid bacteria are still used (e.g., sauerkraut). Because of the lactic acid, the pH drops below 4. Except for the lactic acid bacteria themselves, other bacteria do not tolerate such an acidic environment.
Lactic acid fermentation also plays a role in energy production in the human body. When oxygen in the bloodstream becomes scarce when physical activity is high, muscle cells can temporarily produce ATP through lactic acid fermentation. However, this type of energy production does not work well for too long. The degradation product lactate accumulates over time in the bloodstream and leads in the long term to acidification of the body. Namely, when significantly more lactate is produced than the liver can break down.
Course of lactic acid fermentation
C6H12O6 + 2 ADP + 2 Pi 2C3H6O3 + 2 ATP
Glucose + ADP + phosphate lactic acid + ATP
1. In the first step of the lactic acid fermentation, glycolysis leads to the breakdown of glucose into two pyruvates (pyruvic acid). The high-energy ATP already develops in the course of glycolysis.
2. The enzyme lactate dehydrogenase now serves as a catalyst for the following reaction in which NADH acts as a cofactor: the two pyruvates are reduced to one lactate molecule each. The lactic acid fermentation is completed.
3. Lactate is a metabolic end product that can not be used by the body in this chemical composition. Through the bloodstream, the lactate enters the liver and is oxidized there again to pyruvate. The pyruvic acid is thus used again in the citrate cycle.