During fermentation, yeasts convert glucose into pyruvate through glycolysis, similar to aerobic respiration. However, in the absence of oxygen, pyruvate cannot enter the citric acid cycle (also known as the Krebs cycle) for further energy production. As a result, yeasts divert pyruvate to an alternative pathway known as fermentation.
In alcoholic fermentation, pyruvate is decarboxylated by pyruvate decarboxylase to produce acetaldehyde and carbon dioxide. Acetaldehyde is then reduced to ethanol (alcohol) by alcohol dehydrogenase, utilizing NADH generated during glycolysis. This process allows yeasts to regenerate NAD+ needed for glycolysis to continue, enabling the cell to continue producing energy by converting glucose to ethanol and carbon dioxide.
The production of alcohol in fermentation is beneficial for yeasts as it creates favorable conditions for their survival. It allows them to thrive in environments with limited oxygen, such as fruits, dough, and beverages, where they play vital roles in food production and alcoholic beverage fermentation. Additionally, ethanol has antimicrobial properties, which can inhibit the growth of competing microorganisms, providing a selective advantage to yeasts in certain ecosystems.
