Ethanol alcohol fermentation

Probtom 17.52 In the biochemical conversion of the sugar glucose to ethanol (alcoholic fermentation) a key step is... 

The third major route of pyruvate catabolism leads to ethanol. In some plant tissues and in certain invertebrates, protists, and microorganisms such as brewer s yeast, pyruvate is converted under hypoxic or anaerobic conditions into ethanol and C02, a process called ethanol (alcohol) fermentation (Fig. 14-3). 

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

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. 

Glucose -> 2 Lactate (lactic acid fermentation) Glucose -> 2 Ethanol (alcoholic fermentation) Glucose -> 2 Pyruvate (aerobic subtotal)... 

Reduction of Pyruvate to Ethanol Alcohol Fermentation (Section 21.4B)... 

Alcoholic Fermentation. Certain types of starchy biomass such as com and high sugar crops are readily converted to ethanol under anaerobic fermentation conditions ia the presence of specific yeasts Saccharomyces cerevisia and other organisms (Fig. 6). However, alcohoHc fermentation of other types of biomass, such as wood and municipal wastes that contain high concentrations of cellulose, can be performed ia high yield only after the ceUulosics are converted to sugar concentrates by acid- or enzyme-catalyzed hydrolysis ... 

More recently, interest has developed in the use of enzymes to catalyze the hydrolysis of cellulose to glucose (25—27). Domestic or forest product wastes can be used to produce the fermentation substrate. Whereas there has been much research on alcohol fermentation, whether from cereal grains, molasses, or wood hydrolysis, the commercial practice of this technology is primarily for the industrial alcohol and beverage alcohol industries. About 100 plants have been built for fuel ethanol from com, but only a few continue to operate (28). 

Starches. In the United States, all potable alcohol, most fermentation industrial alcohol, and most fuel alcohol is currendy made principally from grains com is the principal feedstock for fuel alcohol. Fermentation of starch from grain is somewhat more complex than fermentation of sugars because starch must first be converted to sugar and then to ethanol. This process was known to the ancient Egyptians and Mesopotamians who brewed beer almost 5000 years ago (202). The simplified equations for the conversion of starch to ethanol are... 

Alcoholic (ethanolic) fermentation A fermentation in which the major products are carbon dioxide and ethanol (alcohol). 

Alcoholic fermentation, ethanol production, has been best known for a few decades by S. cerevisiae. Many obligate aerobic fungi, such as common moulds of the genera Aspergillus, Fusarium and Mucor are also well known for their ability to produce ethanol.2 The benefits are ... 

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. 

Yeast is used in baking bread because the carbon dioxide bubbles make the bread rise. The other product of alcoholic fermentation is ethanol. Why can t you taste this alcohol when you eat bread ... 

Fayolle et al.12 described work done on alcoholic fermentation, wherein they studied the effects of temperature and various calibration methods. The samples were removed and submitted for HPLC and other conventional analyses. The samples were used as is for MIR spectra generation. PLS-1 was used for equation constmction. The test RSDs for glucose, fructose, glycerol, and ethanol were, respectively, 12.5,6.1, 0.6, and 2.9 g/1. The wavelengths assigned to various components were also listed. 

Fayolle et al. used a remote system to monitor on-line fermentations.15 Both the substrates (glucose, fructose, lactose, and galactose) and the metabolites (ethanol and lactic acid) were monitored. The equations used were built with PLS. The reference method was HPLC. For the alcohol fermentation, glucose, fructose, and ethanol had SEPs (in g/1) of 3.5, 4.5, and 3.8, respectively. For the lactic acid fermentation, the SEPs for lactose, galactose, and lactic acid were 4.1, 1.4, and 2.0, respectively. 

Williams, L.A., Theory and modelling of ethanol evaporative losses during batch alcoholic fermentation. Biotech. Bioeng., 25 (1983) 1597-1612. 

Reductive fermentations can be classified into the following types (1) butyric acid fermentation, (2) butanol-acetone fermentation, (3) butanol-isopropyl alcohol fermentation, (4) butylene glycol-ethanol fermentation, and (5) acetone-ethanol fermentation. 

The manner in which yeast contributes to the fermentation process was not clearly understood until 1857, when the French microbiologist Louis Pasteur discovered that not only does the fermentation process require any oxygen, but also alcohol yield is actually reduced by its presence. The amount of ethanol generated by this first alcoholic fermentation is about 11%. At this step, "champagne" is still actually a noneffervescent white wine, because the carbon dioxide produced during the first alcoholic fermentation is allowed to escape into the atmosphere. 

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