Fermentation, alcoholic lactic

Terms in bold are defined glycolysis 522 fermentation 522 lactic acid fermentation hypoxia 523 ethanol (alcohol) fermentation 523 isozymes 526... 

The product of this metabolic sequence, pyruvate, is a metabolite of caitral importance. Its fate depends upon the conditions within a cell and upon the type of cell. When oxygen is plentiful pyruvate is usually converted to acetyl-coenzyme A, but under anaerobic conditions it may be reduced by NADH + H+ to the alcohol lactic acid (Fig. 10-3, step h). This reduction exactly balances the previous oxidation step, that is, the oxidation of glycer-aldehyde 3-phosphate to 3-phospho-glycerate (steps a and b). With a balanced sequence of an oxidation reaction, followed by a reduction reaction, glucose can be converted to lactate in the absence of oxygen, a fermentation process. The lactic acid fermentation occurs not only in certain bacteria but also in our own muscles under conditions of extremely vigorous exercise. It also occurs continuously in some tissues, e.g., the transparent lens and cornea of the eye. 

During mead fermentation, several problems are generally encountered. For example, the anticipated alcohol content may not be achieved within the time desired. There may also be a lack of uniformity in the final product, due to differences in water content of the honey used. In some situations, such as worts with high sugar contents, successive addition of honey is needed to avoid premature termination of fermentation. This likelihood of stuck fermentation is increased as most mead is made empirically, without adjustments. This can lead to subsequent yeast refermentation and secondary fermentations by lactic and acetic acid bacteria. These can undesirably increase acidity and the production of volatile esters (Casellas, 2005). The presence of these compounds alters... 

Together with proteins and peptides, amino acids constitute the main components of the nitrogenous fraction of musts and wines. They are also the most studied and best known nitrogenated components in wines. Free amino acids in musts are of paramount importance. They constitute a source of nitrogen for yeasts in alcoholic fermentation, for lactic acid bacteria in malolactic fermentation, and can also be a source of aromatic compounds (Kosir and Kidric, 2001). In certain cases, some amino acids... 

After alcohol, lactic acid was the second product obtained industrially from sugar fermentation, starting in 1880. The levo-isomer is still made this way to the tune of 20,000 tons a year. 

Figure 16.12. Maintaining Redox Balance. The NADH produced by the glyceraldehyde 3-phosphate dehydrogenase reaction must be reoxidized to NAD+ for the glycolytic pathway to continue. In alcoholic fermentation, alcohol dehydrogenase oxidizes NADH and generates ethanol. In lactic acid fermentation (not shovm), lactate dehydrogenase oxidizes NADH while generating lactic acid.

How do alcoholic fermentation and lactic acid fermentation differ ... 

See also Lactic Acid Fermentation, Alcoholic Fermenation... 

See also Lactic Acid fermentation. Alcoholic Fermentation... 

Fermentation is defined as an energy-yielding metabolic pathway that involves no net change in oxidation state. Anaerobic glycolysis is a type of fermentation. The lactic acid fermentation (conversion of glucose to lactate) is important in the manufacture of cheese. Another important fermentation involves cleavage of pyruvate to acetaldehyde and C02, with the acetaldehyde then reduced to ethanol by alcohol dehydrogenase in the reaction that follows ... 

The process of making dill pickles does not differ much from that of making sauerkraut as far as the fermentation is concerned. The sugars of the cucumbers diffuse out of the cut cucumbers into the liquor and are fermented by lactic acid bacteria and alcoholic yeasts. As in sauerkraut, B. coli communis and allied bacteria are active fermenters producing hydrogen and carbon dioxide. Oidium lactic finally grows on the surface of the liquor and reduces the acidity. 

In alcoholic fermentation, alcohol dehydrogenase oxidizes NADH and generates ethanol. In lactic acid fermentation (not shown), lactate dehydrogenase oxidizes NADH while generating lactic acid. 

The same lactic bacteria, however, are likely to break down sugars. The consequences may be serious, especially if the wine has a high sugar concentration. The most common situation occurs when alcoholic fermentation stops, leaving the sweet medium open to lactic bacteria. For this reason, winemakers take great care to avoid stuck fermentations, although the bacteria may also take over just before the end of fermentation if it has slowed down. The initial result of this bacterial contamination is malolactic fermentation, but lactic spoilage may follow. This situation must be avoided, especially as the development of these bacteria may prevent the completion of alcoholic fermentation. 

Although species diversity in a must can increase shortly after crush, viable cell number normally remains relatively low (<10 to 10 CFU/mL) for some period of time (Lonvaud-Funel et al., 1991). Even if inoculated prior to alcoholic fermentation, most lactic acid bacteria experience a rapid die-off during alcoholic fermentation, commonly to populations below lOOCFU/mL. As an example, Edwards et al. (1990) observed the population of O. oeni decrease from 10 CFU/mL to less than 30CFU/mL, resulting in a delayed malolactic fermentation. Sometime after completion of alcoholic fermentation, the population of Oenococcus oeni may increase... 

Near-infrared spectroscopy (NIR), which is a nondestructive analytical technique, has been employed for the simultaneous prediction of the concentrations of several substrates, products, and constituents in the mixture sampled from fermentation process. In this chapter, applications of NIR to monitoring of the various fermentation processes are introduced. The fermentation processes mentioned here are wine, beer, Japanese sake, miso (soybean paste), soy sauce, rice vinegar, alcohol, lactic acid, glutamic acid, mushroom, enzymatic saccharification, biosurfactant, penicillin, and compost. The analysis of molasses, which is a raw material of fermentation, with NIR is also introduced. These studies indicate that NIR is a useful method for monitoring and control of fermentation process. 

This is salted sliced cabbage that has undergone fermentation by lactic acid bacteria. In the fermentation process, the sugars of the cabbage are converted primarily to lactic and acetic acids, ethyl alcohol, and carbon dioxide. 

All species are not always represented, or at least cannot be identified by current analytical methods, but a natural selection has been confirmed which takes place progressively during alcoholic fermentation. The lactic population regresses after reaching its optimum. At the same time, the homofermentative then heterofer-mentative lactobacilli disappear, to the benefit of 0. oeni. Afterwards, the homofermentative cocci and L. mesenteroides also give way to O. oeni (see Table 6.4). 

Fermentation When oxygen is absent or in short supply, some cells—such as yeast, some bacteria, and the muscle cells in your body—can break down glucose without oxygen in a process called fermentation. During fermentation, glucose is broken down and a small amount of energy is released. There are two common forms of fermentation. In alcoholic fermentation, ethanol and carbon dioxide are produced. Lactic acid fermentation produces lactic acid. 

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