Fermentation Overview

• Definition: Fermentation is an anaerobic process that follows glycolysis and involves the breakdown of glucose to produce energy without the use of oxygen.

• Key Concepts:

  • Glycolysis occurs in the cytosol and breaks glucose into pyruvate.

  • In the absence of oxygen (O2), fermentation occurs instead of aerobic respiration.

  • Fermentation regenerates NAD+ from NADH, enabling glycolysis to continue.

Types of Fermentation

• Types of Fermentation: Includes glycolysis plus reactions that regenerate NAD+.

  • Alcohol Fermentation

    • First Step: Converts pyruvate to acetaldehyde, releasing CO2.

    • Second Step: Acetaldehyde is reduced to ethanol by NADH.

    • Uses: Conducted by yeast; important for brewing, winemaking, and baking.

  • Lactic Acid Fermentation

    • Process: Pyruvate is directly reduced by NADH to form lactate (or lactic acid) without releasing CO2.

    • Uses: Performed by some fungi and bacteria; used in cheese and yogurt production. In humans, muscle cells utilize this process during strenuous exercise when oxygen is limited to generate ATP.

Fermentation Pathways and Organisms

• Fermentation is carried out by various organisms, which produce different products:

  • Common Organisms:

    • Propionibacterium: Produces CO2 and propionic acid, used in Swiss cheese.

    • Lactobacillus: Produces lactic acid; used in the production of cheddar cheese and yogurt.

    • Saccharomyces: Yeast; produces CO2 and ethanol; used in wine and beer making.

    • Clostridium: Produces acetone and isopropanol, which can be used in nail polish removers.

    • Acetobacter: Produces acetic acid, used in vinegar production.

• Summary of Products:

  • Ethanol: Through alcohol fermentation in yeast.

  • Lactic Acid: By lactic acid fermentation in muscle cells.

  • Carbon Dioxide: Released during alcohol fermentation (first step) and as a byproduct in some bacteria fermentation processes.