Glucose anaerobic fermentation

Product formation stoichiometry can be used to estimate the upper bounds for product yields in processes. A relatively simple example is the anaerobic fermentation of glucose by yeast. Here, carbon dioxide and ethanol are the only products. Modification of (E -3.9) then becomes ... 

PG activity was assayed from cells grown in a medium containing 1% glucose in one-litre self-induced anaerobic fermentation for 5 days by increase of reducing sugars. Enzyme activity increased from pH 3.0 to pH 5.0 (citrate buffer) and decreased drastically above 5.0 (phosphate buffer), but activity was not affected differentially by the two buffers used (data not shown). PG activity increased almost linearly from 20°C to 40°C but above this optimum, activity was lost rapidly and the enzyme was completely inactivated at 60°C and 70°C after 10 and 6 min, respectively (data not shown). No PL, PGL or PME were detected. 

It is among the most capable of invertebrate anaerobes, the helminths and the marine bivalves, that we find the best examples of alternative fermentation pathways. Many of these have been reviewed several times elsewhere, so only a brief summary will be considered here. Current concepts view the organization of anaerobic metabolism as a series of linear, and loosely linked, pathways. The most important of these, aside from classical glucose — lactate fermentation (yielding 2 moles ATP per mole glucose) are summarized by Hochachka and Somero (1984) as follows (see chapter 2) ... 

Fig. 8.8 Processes for 1,3PD (a) from acrolein (Degussa) (b) from ethylene oxide (Shell) (c) from glycerol, via anaerobic fermentation (Henkel) (d) from glucose,...

Oenococcus is a facultative acidophilic anaerobe and grows at pH 4.8 with temperatures between 18 °C and 30 °C. It requires a rich medium supplemented with tomato juice or grape juice, and its growth is not inhibited in the presence of 10% ethanol. Glucose is fermented in lactic acid, carbon dioxide, acetic acid and ethanol (it is a heterofermenter). It converts malate into lactate and CO2 in the presence of fermentable carbohydrate. 

Using Brettanomyces claussenii, Custers showed glucose fermentation is inhibited under anaerobic conditions. Glucose was fermented more rapidly under aerobic than anaerobic conditions. He named this inhibitory effect a negative Pasteur effect". Aerobic conditions activated the fermentation of glucose to produce ethyl alcohol, carbon dioxide, and "a considerable amount of acetic acid". Only ethanol and carbon dioxide were produced under anaerobic conditions acetic acid was not. 

The first metabolic pathway that we encounter is glycolysis, an ancient pathway employed by a host of organisms. Glycolysis is the sequence of reactions that metabolizes one molecule of glucose to two molecules ofpyruvate with the concomitant net production of two molecules of ATP. This process is anaerobic (i.e., it does not require O2) inasmuch as it evolved before the accumulation of substantial amounts of oxygen in the atmosphere. Pyruvate can be further processed anaerobically (fermented) to lactate (lactic acidfermentation) or ethanol (alcoholic fermentation). Under aerobic conditions, pyruvate can be completely oxidized to CO2, generating much more ATP, as will be discussed in Chapters 17 and 18. 

In the anaerobic fermentation of grain, the yeast Saccharomyces cerevisiae digests glucose from plants to form the products ethanol and propenoic acid by the following overall reactions ... 

Biochemical reactions such as aerobic and anaerobic fermentations occur in the presence of living organisms or cells, such as bacteria, algae, and yeast. These reactions can be considered as biocatalyzed by the organism. Thus in a typical bioreactor a substrate (such as glucose) is fed into the fermenter or bioreactor in the presence of an initial amount of cells. The desired product can be the cells themselves or a secreted chemical called a. metabolite. In either case the cells multiply in the presence of the substrate, and the rate of production of cells is proportional to the concentration of the cells— hence this process is autocatalytic. In a batch reactor with ample... 

Over half the known species of yeasts can ferment D-glucose anaerobically (see Table III). Saccharomyces cerevisiae ferments both a- and /3-D-glucopyranose at about the same rate.176 In the anaerobic fermentation of sugars, yeasts convert the pyruvate produced by glycolysis into ethanol by way of acetaldehyde. 

Acetone-butanol-ethanol (3 6 1) mixture by anaerobic fermentation of glucose Clostridium acetobutylicum... 

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