Fermentation acetic

The overall reaction of glucose catabolism to lactate and acetate fermentation from 2 moles of glucose yields 2 moles of lactic acid, 3 moles of acetic acid and 5 moles of ATP, as shown below ... 

The conversion of ethyl alcohol by way of acetaldehyde into acetic acid is the chemical expression equivalent to acetic fermentation. In this process the acetic bacteria utilise atmospheric oxygen in order to bind the hydrogen. That the hydrogen which has to be removed is activated, and not the oxygen (as was formerly thought), is shown by experiments in which oxygen is eaxluded and replaced by quinone the bacteria produce acetic acid from alcohol as before and the quinone is reduced to hydroquinone. 

Figure 11.2. General features of the C02-reduction and acetate fermentation pathways showing reactions unique and common to each.

Table 11.3. Reactions unique to the acetate fermentation pathway and enzymes that catalyze them.

The carbonic anhydrase (Cam) in M. thermophila cells is elevated several fold when the energy source is shifted to acetate, suggesting a role for this enzyme in the acetate-fermentation pathway. It is proposed that Cam functions outside the cell membrane to convert CO2 to a charged species (reaction A4) thereby facilitating removal of product from the cytoplasm. Cam is the prototype of a new class (y) of carbonic anhydrases, independently evolved from the other two classes (a and P). The crystal structure of Cam reveals a novel left-handed parallel P-helix fold (Kisker et al. 1996). Apart from the histidines ligating zinc, the activesite residues of Cam have no recognizable analogs in the active sites of the a- and P-classes. Kinetic analyses establish that the enzyme has a zinc-hydroxide mechanism similar to that of Cab (Alber et al. 1999). 

CO2, selected Ci -C2 compounds Acetate fermentation CH3COOH CH4 + CO2 CO2 reduction C02 + 4H2 CH4 + 2H20... 

Methanogenesis H2 C02 OO2, possibly formate, acetate 4H2+ CO2 CH4 + 2H2O (CO2 reduction) CH3COOH CH4 + CO2 (acetate fermentation) Mesophilic to hyperthermophilic archaea at vents and seeps... 

During microbial action, kinetic isotope fractionations on the organic material by methanogenic bacteria result in methane that is highly depleted in typically with 5 C-values between -110 and -50%c (Schoell 1984, 1988 Rice and Claypool 1981 Whiticar et al. 1986). In marine sediments, methane formed by CO2 reduction is often more depleted in than methane formed by acetate fermentation in freshwater sediments. Thus, typical ranges for marine sediments are between -110 and -60%c, while those for methane from freshwater sediments are from -65 to -50%c (Whiticar et al. 1986 Whiticar 1999). 

Whiticar MJ, Faber E, SchoeU M (1986) Biogenic methane formation in marine and freshwater environments CO2 reduction vs. acetate fermentation-isotopic evidence. Geochim Cosmochim Acta 50 693-709... 

Of the different organisms causing alterations and diseases in wine, only those associated with " fleurs de vin and acetous fermentation can be identified with certainty. 

Acetous fermentation [souring) is caused by Mycoderma aceti, which consists of oval cells with a marked constriction in the middle, resemblance to the figure 8 being thus produced. The cells are considerably smaller (about 10 times) than those of M. vini. In some cases several individuals are joined in a chain. 

Acetic acid (CH3COOH) is a bulk commodity chemical with a world production of about 3.1 x 106 Mg/year, a demand increasing at a rate of +2.6% per year and a market price of US 0.44-0.47 per kg (Anon., 2001a). It is obtained primarily by the Monsanto or methanol carbonylation process, in which carbon monoxide reacts with methanol under the influence of a rhodium complex catalyst at 180°C and pressures of 30-40 bar, and secondarily by the oxidation of ethanol (Backus et al., 2003). The acetic fermentation route is limited to the food market and leads to vinegar production from several raw materials (e.g., apples, malt, grapes, grain, wines, and so on). 

Chukwu, U.N. and Cheryan, M. 1999. Electrodialysis of acetate fermentation broths. Appl. Biochem. Biotech. 77-79, 485 199. 

Using glucose as a model substrate, hydrogen production is accompanied with either acetate formation (Eq. (15.1) or butyrate formation (Eq. (15.2) (Miyake, 1998). In the acetate fermentation 4 ATPs are produced whereas, 3 ATPs are produced in the butyrate fermentation. Thus, it seems that the acetate fermentation is energetically more favorable than the butyrate fermentation. However, acetate and butyrate fermentations are commonly carried... 

These figures are only theoretical, however, as other substances may also be produced during acetic fermentation and these alter the figures in practice. In general terms, it can be said that 1% by volume of alcohol yields about 1% of acetic acid. 

The acetic acid bacteria are introduced either as mother of vinegar or as a liquid culture. Small producers often use mother of vinegar. This consists of acetic acid bacteria and slime bacteria. The latter are responsible for the consistency of the mother of vinegar. They also produce metabolites, however, and for this reason acetic fermentation by mother of vinegar is not always completely pure in tone. 

Air is needed by the bacteria for their work . For acetic fermentation to start, the must has to be adequately aerated. Open storage alone is often not enough. 

In this process the acetic fermentation takes place in a more or less open container (usually a vinegar vat in the cellar). The primary product stays in the open container until acetic fermentation starts, i.e. a mother of vinegar, or film consisting of vinegar bacteria, moulds and slime fungi, is formed. In this method it is not possible to control the fermentation or the temperature. The quality of the vinegar produced does not always meet current sensory and analytical requirements. 

In the case of vinegar, the percentage acid content ( Acid content. ..% ) and the kind of vinegar must also be stated. Vinegar made by acetic fermentation of an alcoholic liquid is described as Pure fermentation vinegar . 

A second site for ATP synthesis in acetate fermentation appears be the oxidation of the enzyme-bound CO to CO2. This was deduced from the following findings cell suspensions of Methanosarcina barkeri catalyze the oxidation of free CO to CO2 with as electron acceptor, when methanogenesis is inhibited by bromoethanesulfonate [233] ... 

Free energy changes (AG° ) and redox potentials ( " ) of partial reactions involved in acetate fermentation to CH4 and CO2 in Methanosarcina barkeri ... 

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