Alcoholic Fermentation - Yeasts
Yeasts, which usually have a round shape and a size of between 2 and 4 μm, can be found naturally in certain foods such as fruits, cereals, and vegetables. These organisms are known as facultative anaerobes, which means they can function without oxygen.
Microscopic fungi, including species such as Saccharomyces cerevisiae, Kluyveromyces fragilis, Torulaspora, and Zymomonas mobilis, are responsible for approximately 96% of ethanol production. Yeasts are one of the three types of microorganisms involved in fermentation, along with bacteria and molds.
Each microorganism has its unique function in fermentation, capable of producing a characteristic flavor in the final product, such as in the case of wines or beers. The fermentation process may involve the joint work of multiple microorganisms.
Yeasts, which have been used as an industrial byproduct in human food, can be immobilized to enhance their enzymatic attack on carbohydrate substrates, prevent their spread, and facilitate their recovery. To achieve this, fixatives such as agar, calcium alginate, and balsamic wood chips are usually used, as biocatalysts can be expensive.
Zymomonas mobilis is a bacterial strain with high fermentation efficiencies that does not require immobilization, even at relative motility rates, as confirmed by its complete genome made public in 2005. However, it is not used for beer and cider fermentation due to its unpleasant flavors and odors.
Nevertheless, it has great resistance to survive at high concentrations of ethanol, making it an ideal bacterium for generating ethanol for non-edible uses such as biofuels. Zymomonas mobilis was first described by biologist Lindner in 1928 and is known as Z. lindneri, Thermobacterium mobilis, or Pseudomonas lindneri in honor of its discoverer. One of its unique characteristics is the use of the Entner-Doudoroff pathway for glucose metabolism instead of the more common Embden-Meyerhoff-Parnas pathway.
