maitohappokäymisenä

Maitohappokäyminen, known in English as lactic acid fermentation, is a metabolic process that converts sugars into lactic acid. This anaerobic process occurs in certain bacteria, such as lactobacilli, and also in muscle cells during strenuous exercise when oxygen supply is insufficient.

During lactic acid fermentation, a sugar molecule, typically glucose, is broken down into pyruvate through glycolysis. In the absence of oxygen, pyruvate is then converted directly into lactic acid by the enzyme lactate dehydrogenase. This regeneration of NAD+ from NADH is crucial for glycolysis to continue, allowing for the production of ATP, the cell's energy currency.

In the food industry, lactic acid fermentation is fundamental to the production of various dairy products like yogurt, cheese, and kefir. The lactic acid produced lowers the pH, which helps to preserve the food and contributes to its characteristic sour taste and texture. It is also utilized in the fermentation of sauerkraut, kimchi, and other pickled vegetables, as well as in the production of sourdough bread.

In the context of human physiology, lactic acid can accumulate in muscle tissue during intense physical activity. While this accumulation was once thought to be solely responsible for muscle fatigue and soreness, current understanding suggests it is a temporary byproduct and can be converted back to pyruvate or glucose in the liver when oxygen becomes available.