Lactic acid, ethanol reaction

The above observations suggested that hexoses arise in Nature by reaction of glycerose with dihydroxyacetone. A vast amount of practical information has been derived from investigation of plant- and muscle-extracts, two dissimilar systems that show many similarities in their biosynthetic manipulations. There is a close parallelism in the sequence of intermediates involved in the processes wherein D-glucose is converted to ethanol and carbon dioxide by yeasts, and to lactic acid by muscle during contraction. The importance of these schemes lies in their reversibility, which provides a means of biosynthesis from small molecules. 

Aqueous phase reforming of glycerol in several studies by Dumesic and co-workers has been reported [270, 275, 277, 282, 289, 292, 294, 319]. The first catalysts that they reported were platinum-based materials which operate at relatively moderate temperatures (220-280 °C) and pressures that prevent steam formation. Catalyst performances are stable for a long period. The gas stream contains low levels of CO, while the major reaction intermediates detected in the liquid phase include ethanol, 1,2-pro-panediol, methanol, 1-propanol, propionic acid, acetone, propionaldehyde and lactic acid. Novel tin-promoted Raney nickel catalysts were subsequently developed. The catalytic performance of these non-precious metal catalysts is comparable to that of more costly platinum-based systems for the production of hydrogen from glycerol. 

The yield of 1,3-PD for this reaction is 67% (mol/mol). If biomass formation is considered the theoretical maximal yield reduces to 64%. In the actual fermentation a number of other by-products are formed, i. e., ethanol, lactic acid, succinic acid, and 2,3-butanediol, by the enterobacteria Klebsiella pneumoniae, Citrobacter freundii and Enterobacter agglomerans, butyric acid by Clostridium butyricum, and butanol by Clostridium pasteurianum (Fig. 1). All these by-products are associated with a loss in 1,3-PD relative to acetic acid, in particular ethanol and butanol, which do not contribute to the NADH2 pool at all. 

In this chapter we describe the individual reactions of glycolysis, gluconeogenesis, and the pentose phosphate pathway and the functional significance of each pathway. We also describe the various fates of the pyruvate produced by glycolysis they include the fermentations that are used by many organisms in anaerobic niches to produce ATP and that are exploited industrially as sources of ethanol, lactic acid, and other... 

When grown in alkaline media, certain species of lactic acid bacteria decrease production of LDH, resulting in increased formation of formate, acetate, and ethanol as end products. This phenomenon has been observed in S. faecalis subsp. liquefaciens (Gunsalus and Niven 1942), Streptococcus durans, S. thermophilus, (Platt and Foster 1958), and Lactobacillus bulgaricus (Rhee and Pack 1980). Data of Rhee and Pack (1980) indicate that a phosphoroclastic split of pyruvate occurs under alkaline conditions to yield ATP. The enzymes involved in this reaction (pyruvate formate-lyase and acetate kinase) require alkaline conditions for optimum activity. A shift from homo- to heterofermentation because of increased pH has not been observed for Group N streptococci. 

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.

A requirement for all fermentations is the existence of a mechanism for coupling ATP synthesis to the fermentation reactions. In the lactic acid and ethanol fermentations this coupling mechanism consists of the formation of the intermediate 1,3-bisphosphoglycerate by the glyceraldehyde 3-phosphate dehydrogenase (Fig. 10-3, step a). This intermediate contains parts of both the products ATP and lactate or ethanol. 

Some lactic acid bacteria of the genus Lactobacillus, as well as Leuconostoc mesenteroides and Zymomonas mobilis, carry out the heterolactic fermentation (Eq. 17-33) which is based on the reactions of the pentose phosphate pathway. These organisms lack aldolase, the key enzyme necessary for cleavage of fructose 1,6-bisphosphate to the triose phosphates. Glucose is converted to ribulose 5-P using the oxidative reactions of the pentose phosphate pathway. The ribulose-phosphate is cleaved by phosphoketolase (Eq. 14-23) to acetyl-phosphate and glyceraldehyde 3-phosphate, which are converted to ethanol and lactate, respectively. The overall yield is only one ATP per glucose fermented. 

Tills is generally associated with the familiar alcoholic fermentation in which theoretically 100 parts of glucose are converted to 51.1 parts of ethyl alcohol (ethanol). 48.9 parts of carbon dioxide (CO/i. and heat. In addition, however, the anaerobic reaction also yields minor byproducts in small amounts—mainly glycerol, succinic acid, higher alcohols (fusel oil), 2,3-butanediol, and traces of acetaldehyde, acetic acid, and lactic acid. Fusel oil is a mixture of alcohols, including -propyl, -butyl, isobutyl, amyl, and isoamyl alcohols. 

Oxidation of compounds of the types thus far discussed proceeds readily at room temperature. Certain compounds which show no substantial reaction with periodic acid at room temperature can be oxidized at elevated temperature.22- 23 26 Thus, at 100° in aqueous solution the acetone mole exile is split to produce acetic acid and formaldehyde diethyl ketone yields propionic acid and probably ethanol lactic acid gives acetaldehyde and carbon dioxide acetaldehyde is oxidized to formic acid and methanol, which is converted into formaldehyde and pyruvic acid yields acetic acid and carbon dioxide. 

Sodium Stearoyl Lactylate occurs as a cream-colored powder or brittle solid. It is a mixture of sodium salts of stearoyl lactylic acids and minor proportions of other sodium salts of related acids, manufactured by the reaction of stearic acid and lactic acid, neutralized to the sodium salts. It is slightly hygroscopic. It is soluble in ethanol and in hot oil or fat, and is dispersible in warm water. 

Malolactic fermentation (MLF) in wine is by definition the enzymatic conversion of L-malic acid to L-lactic acid, a secondary process which usually follows primary (alcoholic) fermentation of wine but may also occur concurrently. This reduction of malic acid to lactic acid is not a true fermentation, but rather an enzymatic reaction performed by lactic acid bacteria (LAB) after their exponential growth phase. MLF is mainly performed by Oenococcus oeni, a species that can withstand the low pFi (<3.5), high ethanol (>10 vol.%) and high SO2 levels (50 mg/L) found in wine. More resistant strains of Lactobacillus, Leuconostoc and Pediococcus can also grow in wine and contribute to MLF especially if the wine pH exceeds 3.5 (Davis et al. 1986 Wibowo et al. 1985). The most important benefits of MLF are the deacidification of high acid wines mainly produced in cool climates, LAB contribute to wine flavour and aroma complexify and improve microbial sfabilify (Lonvaud-Funel 1999 Moreno-Arribas and Polo 2005). 

Grbin et al. 2007). ATHP reduction may lead to EHTP. As ethanol is a precursor, mousy off-flavour occurs after alcoholic fermentation, preferably after lactic acid bacteria activity. It seems that the formation of mousiness may be induced by oxidation but it is not clear if the effect is on the microorganisms or in any chemical reaction stimulated by the redox potential. Other agents claimed to affect its production (high pH, low sulphite, residual sugar content) (Lay 2004 Snowdon et al. 2006 Romano et al. 2007) are also stimulators of microbial activity and so the true mechanisms are not yet clarified, but the non-enzymatic chemical synthesis has been ruled out in D. anomala (Grbin et al. 2007). 

Figure 16.12. Maintaining Redox Balance. The NADH produced by the glyceraldehyde 3-phosphate dehydrogenase reaction must be reoxidized to NAD+ for the glycolytic pathway to continue. In alcoholic fermentation, alcohol dehydrogenase oxidizes NADH and generates ethanol. In lactic acid fermentation (not shovm), lactate dehydrogenase oxidizes NADH while generating lactic acid.

The photolysis of organic materials has also been accomplished by the oxidative quenching of photosensitizers. For example, oxidative quenching of Ru(bpy)3 by MV + in the presence of NADH leads to MV+ and NAD+ through the sequence of reactions outlined in Eqs. 15-17. The reduced photoproduct, MV, mediates H2 evolution in the presence of Pt colloid (Eq. 18), while NAD mediates the two-electron oxidation of ethanol (Eq. 19) or lactic acid (Eq. 20) biocatalyzed by the respective enzyme [225]. 

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