Saccharomyces cerevisiae
嗜酸乳杆菌
Fermentation is a form of anaerobic catabolism in which an organic compound is both an electron donor and an electron acceptor. Fermentation used as a way of harvesting chemical energy without using either oxygen or any electron transport chain, in other words, without cellular respiration. In fermentation, ATP is produced through a substrate-level phosphorylation.
Glycolysis will begin the process of glucose metabolism, generating pyruvate. Fermentation converts pyruvate into lactic acid or ethyl alcohol (ethanol). The two most commonly occurring fermentation pathways are homolactic acid fermentation and alcoholic fermentation. In both forms of fermentation, NAD+is regenerated from NADH, and glycolysis can thus continue.
Fermentation, by definition, is anaerobic; the process it self does not require oxygen. Aerobic fermentation means that oxygen is present in the environment when the fermentation process takes place (e.g. oxygen is pumped into the bioreactor where bioethanol fermentation takes place).
Alcohol fermentation
In alcohol fermentation, pyruvate is converted into ethanol (ethyl alcohol) while releasing carbon dioxide in the process. There are two step involved in pyruvate conversion:
- Release carbon dioxide from the pyruvate, which is converted to the two-carbon compound acetaldehyde
- Acetaldehyde reduction by NADH to ethanol.
These step provide continous supply of NAD+for ATP generating glycolysis. One of the microorganism that can perform alcohol fermentation is yeast such asSaccharomyces cerevisiae.
Lactic Acid fermentation
In lactic acid fermentation, pyruvate is converted directly to lactate, with no release of carbon dioxide. Lactic acid fermentation are perform by certain fungi and lactic acid bacteria. These type of fermentation have been utilized for production of cheese(Lactobacillus lactis), yogurt (嗜酸乳杆菌,Streptococcus thermophilus, andLactobacillus bulgaricus), and other fermented dairy products.