Piimhappekäärimine

Piimhappekäärimine, also known as lactic acid fermentation, is a metabolic process that converts sugars such as glucose into lactic acid. This process occurs in muscle cells during strenuous exercise when oxygen supply is insufficient for aerobic respiration. It is also carried out by certain bacteria, notably those in the Lactobacillaceae family, which are vital in the production of fermented dairy products like yogurt, cheese, and kefir.

The biochemical pathway for lactic acid fermentation involves glycolysis, where glucose is broken down into pyruvate. In the absence of oxygen, pyruvate is then converted to lactic acid by the enzyme lactate dehydrogenase. This regeneration of NAD+ from NADH allows glycolysis to continue, producing a small amount of ATP, the cell's energy currency.

In food production, lactic acid bacteria play a crucial role. They consume lactose, the sugar found in milk, and produce lactic acid. This acid lowers the pH of the milk, causing proteins like casein to denature and coagulate, resulting in the thickened texture characteristic of yogurt and the formation of curds in cheese. The lactic acid also contributes to the tangy flavor and acts as a preservative by inhibiting the growth of spoilage microorganisms. Different species of lactic acid bacteria are used to achieve specific flavors and textures in various fermented foods.