Alcoholic fermentation yeast species

In alcoholic fermentation (also called ethanol fermentation) yeast species, such as Sac-charomyces cerevisiae, convert carbohydrates, mainly sucrose or glucose, under anaerobic conditions into ethanol, and carbon dioxide (Figure 4A.23). 

Lactose-fermenting yeasts have been known for some time, but their use to produce ethyl alcohol and yeast from whey received serious attention only much later. Certain Torula species yield more alcohol than might have been expected from statements in the literature. Four kefir yeasts, two Torula species, one of Torulopsis and one additional yeast species, produced alcohol yielding 68 to 80% of the theoretical quantity. A maximal yield, 80.3%, based on a theoretical yield of 4 moles of alcohol per mole of lactose fermented, was obtained with a strain of Torula cremoris in a 21.7-hr fermentation at 30 to 32°C (Marth 1974). 

In addition to S02 and antibacterial proteins/peptides, medium-chain fatty acids produced by yeast during alcoholic fermentation have also been implicated in the inhibition of malolactic bacteria (Carrete et al, 2002 Edwards and Beelman, 1987 Lonvaud-Funel et al, 1985). Inhibition of Saccharomyces species and some LAB by medium-chain fatty acids has been reported in grape juice and silage (Pederson et al, 1961 Woolford, 1975). Although this hypothesis has not been conclusively shown, Lonvaud-Funel et al (1985) and... 

Fermentation is the name conventionally attributed to any industrial transformation that involves microorganisms. In TBV production, there are two distinct fermentations alcoholic and acetic the first is carried out by yeasts of different genera and species, the second by AAB. Usually, the two fermentations occur in the same vessel (badessa) and are performed by wild strains without any control. The results are unpredictable sometimes the alcoholic fermentation is inhibited by acetic acid produced by AAB often the acetic acid fermentation, for various reasons, does not occur. To solve the problem, a two-stage fermentation procedure has been suggested the oxidation of ethanol should always follow alcoholic... 

Alcoholic fermentation occurs in yeast and several bacterial species. In yeast, pyruvate is decarboxylated to form acetaldehyde, which is then reduced by NADH to form ethanol. (In a decarboxylation reaction, an organic acid loses a carboxyl group as COz.)... 

Alcoholic fermentation by certain yeasts is used commercially to produce wine, beer, and bread (Special Interest Box 8.1). Certain bacterial species produce alcohols other than ethanol. For example, Clostridium acetobutylicum, an organism related to the causative agents of botulism and tetanus, produces butanol. Until recently, this organism was used commercially to synthesize butanol, an alcohol used to produce detergents and synthetic fibers. A petroleum-based synthetic process has now replaced microbial fermentation. 

Yeasts are one of the most important causes of food spoilage. S. cerevisiae, used for the leavening of bread and alcoholic fermentation, can cause spoilage in juices due to the production of alcohol and CO2. Inactivation by PEF of several yeast and mold species (Zhang et al., 2007) including Saccharomyces species (Qin et al., 1994, 1995c ... 

The yeast responsible for alcoholic fermentation in winemaking is usually introduced into the must from the surface of the grapes, the surface of winery equipment, or from specifically prepared cultures. The fermentation process can occur either naturally, without inoculation, or by inoculating the must with selected starters. The use of locally selected yeast strains (usually belonging to the species Saccharomyces cereoisiae), with strain-specific metabolic characteristics can positively affect the final quality of the wine (Regodon et al., 1997 Romano et al., 2003). Several studies have clearly shown the effects of indigenous and inoculated yeast populations on the wine volatile composition (Mateo et al., 2001 Nurgel et al, 2003). 

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