Acetic acid/acetate fermentation

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 ... 

Llangwell A process for making acetic acid by fermenting the cellulose in com cobs. Xylose is a co-product. The microorganism was isolated from the gut of the goat. Piloted on a large scale by the Commercial Solvents Company, Terre Haute, IN, from 1928 to 1930. 

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. 

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). 

Weier, A.J., Glatz, B.A., and Glatz, C.E. 1992. Recovery of propionic and acetic acids from fermentation broths by electrodialysis. Biotechnol. Prog. 8, 479-485. 

Separation of propionic and acetic acid from fermentation broth... 

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. 

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 . 

Acetic Fermentation.—Acetic acid in addition to its occurrence in nature in the form of esters is produced on the large scale by the acid fermentation (oxidation) of the alcohol obtained as the result of fermenting fruit juices which contain sugar, especially apple juice or cider, and wine. When the sugar present in cider is fermented, dueTo the action of the enzyme zymase, alcohol is produced (p. 95). This alcohol is then oxidized through the activity of an aerobic bacterial organism Bacterium aceti, which is present naturally in the fruit juice. The product is acetic acid. 

Volatile Acids Kinetics. In evaluating the methane fermentation kinetics of the three volatile acids chosen for study, it was necessary to consider the process biochemistry and stoichiometry. According to Barker (19), acetic acid is fermented to methane and carbon dioxide in a single step while both propionic and butyric acids are fermented in two steps. In the first step these acids are fermented to acetic acid and methane by species of methanogenic bacteria. The resulting acetic acid is then fermented by different methanogenic species to methane and carbon dioxide. The stoichiometry of these fermentations is shown by the following equations (19). 

Besides the production of L-lactic acid, the fermentation process can simultaneously produce various other metabolites such as acetic acid, f umaric acid, ethanol, malic acid, etc. However, the amount of these metabolites can have a significant influence on the downstream process and the quality of the L(+)-lactic acid produced (Wang et al., 2005). Fumaric acid is the main by-product and its accumulation is affected by many factors,... 

It is, however, unclear if it contributes to acetic acid resistance in acetic fermentation (Nakano, Fukaya, and Horinouchi, 2006). 

---