Ethanol in fermentation

Figure 10-3 Coupling of the reactions of glycolysis with formation of lactic acid and ethanol in fermentations. Steps a to g describe the Embden-Meyerhof-Parnas pathway. Generation of 2 ATP in step b can provide all of the cell s energy.

When cellulose is used as a raw material, the activity of cellulase (the enzyme catalyzing cellulose hydrolysis) is inhibited by glucose and short cellulose chains. One way to overcome this inhibition is to combine enzymatic hydrolysis with glucose fermentation to ethanol, as the accumulation of ethanol in fermenter does not inhibit cellulase. 

Cavinato, A. G., et al. "Noninvasive Method for Monitoring Ethanol in Fermentation Processes Using Fiber-Optic Near-Infrared Spectroscopy." Analytical Chemistry, 621990,1978-1982. 

A. G. Cavinato, D. M. Mayes, Z. Ge, J. B. CalUs. Noninvasive method for monitoring ethanol in fermentation processes using fiber-optic near infrared spectroscopy. Ana/ Chem 62 1977-1982,1990. 

The static headspace technique is very simple and quick. The procedure is well documented in the literature, and for many applications the sensitivity is more than adequate, so that its use is usually favoured over that of the P8dT technique. There are areas of application where good results are obtained with the static headspace technique which cannot be improved upon by the P8dT method. These include the forensic determination of alcohol in blood, of free fatty acids in cell cultures, of ethanol in fermentation units or drinks and residual water in polymers. This also applies to studies on the determination of ionization constants of acids and bases and the investigation of gas phase equilibria. 

Because oil and gas ate not renewable resources, at some point in time alternative feedstocks will become attractive however, this point appears to be fat in the future. Of the alternatives, only biomass is a renewable resource (see Fuels frombiomass). The only chemical produced from biomass in commercial quantities at the present time is ethanol by fermentation. The cost of ethanol from biomass is not yet competitive with synthetically produced ethanol from ethylene. Ethanol (qv) can be converted into a number of petrochemical derivatives and could become a significant source. 

The sugars in fruits such as grapes are feimented by yeasts to produce wines. In winemaking, lactic acid bacteria convert malic acid into lactic acid in malolactic fermentation in fruits with high acidity. Acetobacter and Gluconobacter oxidise ethanol in wine to acetic acid (vinegar). 

Fermentation of sugar by Saccharomyces cerevisiae, for production of ethanol in an immobilised cell reactor (ICR), was successfully carried out to improve the performance of the... 

Fig. 8.6. Glucose concentration, cell density and production of ethanol in batch fermentation with initial concentration of 50 g-l 1 glucose versus time. Reprinted from Najafpour et al. (2004).18 Copyright with permission from Elsevier.

In fermentation for the production of acetic acid, ethyl alcohol is used in an aerobic process. In an ethanol oxidation process, the biocatalyst Acetobacter aceti was used to convert ethanol to acetic acid under aerobic conditions. A continuous fermentation for vinegar production was proposed for utilisation of non-viable A. aceti immobilised on the surface of alginate beads. 

In the manufacture of absolute alcohol by fermentation, the product is separated and purified using several stages of distillation. In the first stage, a mixture of 5 mol per cent ethanol in water, with traces of acetaldehyde and fusel oil, is concentrated to 50 mol per cent. The concentration of alcohol in the wastewater is reduced to less than 0.1 mol per cent. 

Fermenting grains with yeast produces a grain alcohol. The process also works with other biomass feedstocks. In fermentation, the yeast decomposes carbohydrates which are starches in grains, or sugar from sugar cane juice into ethyl alcohol (ethanol) and carbon dioxide. The process breaks down complex substances into simpler ones. 

Virtually any source of glucose can undergo alcoholic fermentation—lOOg of potatoes in an oxygen-free atmosphere at 22°C will give 600 mg of ethanol in 8 days—the product is pretty unpalatable, but distillation can change that. 

Microorganisms have also been developed to produce alternative products, such as lactic acid [65], propane-1,3-diol [67], 3-hydroxypropionic acid [68], butane-2,3-diol [69] and numerous other intermediates. For instance, bacteria such as the Clostridium acetobutylicum ferment free sugars to C4 oxygenates such as butyric acid or butanol. They form the C4 oxygenates by Aldol condensation of the acetaldehyde intermediates. The Weizmann process exploits this property to ferment starch feedstock anaerobically at 37 °C to produce a mixture of w-butanol, acetone and ethanol in a volume ratio of 70 25 5 [3],... 

As discussed in previous sections, sugars, starch and (ligno)cellulose can be converted into ethanol by fermentation, the latter via preliminary chemical and physical pretreatment followed by enzymatic breakdown of the biopolymers. Pure ethanol can be added to gasoline or diesel. However, this requires an energy-intensive distillation step. This and the energy used in fertilizers, transportation... 

Schuster et al. reported work on monitoring a complex ace-tone-butanol-ethanol (ABE) fermentation system.22 They looked at the qualitative nature of the biomass as well as the solvents present in the liquid phase. A hierarchical cluster analysis was performed on samples from various times of the fermentation. The clusters were then classified using classical markers and analyses. The resultant table, combining qualitative interpretation and quantitative results, shows an interesting mosaic of the system over time. Total solvents, optical density, and butyric acid are given as numeric values in either absorbance units of g/1. 

Ethanol is the major intoxicant in drinks that are made by the fermentation of sugar solutions by yeasts and is the most widely used non-therapeutic drug. A small sherry or whisky can raise the concentration of ethanol in the blood to 2-A mmol/L. Ethanol is taken up and metabolised by the liver but, if large quantities are consumed, the Uver cannot increase the rate of utilisation and the plasma concentration can reach 0.1 M/L, which can damage the liver (see below). 

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