Certain organisms perform fermentation to obtain the energy they need to carry on their life processes. (Most organisms obtain the energy for these processes through aerobic respiration , in the presence of free oxygen.) Various microorganisms, including yeasts and certain molds and bacteria, obtain their energy through fermentation. Many of the fermentation processes result in products that are important in medicine, food preparation, and other fields.
The specific product resulting from fermentation is determined by the type of microorganism carrying on the process and the substance in which the fermentation occurs. For example, wine is the product of yeast fermentation in fruit juice, while beer is the product of yeast fermentation in grain. Vinegar and cheese are products of bacterial fermentation. Yeast fermented in the leavening of bread.
Food fermentation has been said to serve five main purposes:
- Enrichment of the diet through development of a diversity of flavors, aromas, and textures in food substrates
- Preservation of substantial amounts of food through lactic acid, alcohol, acetic acid, and alkaline fermentations
- Biological enrichment of food substrates with protein, essential amino acids, and vitamins
- Elimination of antinutrients
- A decrease in cooking time and fuel requirement
How It Works
Yeast and certain bacteria perform ethanol fermentation where pyruvate (from glucose metabolism) is broken into ethanol and carbon dioxide. The net chemical equation for the production of ethanol from glucose is:
CHO (glucose) → 2 CHOH (ethanol) + 2 CO (carbon dioxide)
Ethanol fermentation is used the production of beer, wine and bread. It's worth noting that fermentation in the presence of high levels of pectin result in the production of small amounts of methanol, which is toxic when consumed.
Lactic Acid Fermentation
The pyruvate molecules from glucose metabolism (glycolysis) may be fermented into lactic acid. Lactic acid fermentation is used to convert lactose into lactic acid in yogurt production. It also occurs in animal muscles when the tissue requires energy at a faster rate than oxygen can be supplied. The next equation for lactic acid production from glucose is:
CH O (glucose) → 2 CH CHOHCOOH (lactic acid)
The production of lactic acid from lactose and water may be summarized as:
CH O (lactose) + H O (water) → 4 CH CHOHCOOH (lactic acid)