Decomposition reactions fermentation

The distinctive aroma of ammonia is often apparent in bakeries but not in the final product. Bakers yeast performs its leavening function by fermenting such sugars as glucose, fructose, maltose, and sucrose. The principal products of the fermentation process are carbon dioxide gas and ethanol, an important component of the aroma of freshly baked bread. The fermentation of the sugar, glucose—an example of a decomposition reaction — is given by the equation in Fig. 5.19.1. 

Figure 5.19.1 The fermentation of glucose to yield ethanol and carbon dioxide (a decomposition reaction).

Autohydrolysis enables the selective hydrolysis of hemicelluloses to a mixture mainly consisting of oligosaccharides and monosaccharides. The monosaccharide content can be increased under harsher reactor conditions, but then monosaccharides can undergo decomposition reactions, thereby increasing the content of potential fermentation inhibitors in hydrolysates. 

One of the most important anaerobic pathways of decomposition in marine sediments is sulfate reduction (Berner, 1964 Goldhaber and Kaplan, 1974 J0rgenson, 1977). Proof that sulfate reduction is taking place in surface sediments at each station of this study comes from the abundance of fixed sulfur in the solid phase and the presence in the pore waters of dissolved sulfide (Figs. 31-34 Appendix B Goldhaber et ai, 1977). Because sulfate reduction presumably dominates the anaerobic decomposition reactions over most of the sampled sediment regions, reaction 5 of Table IV will be assumed as the major model reaction to aid in the interpretation of pore-water and solid-phase property distributions. Additional decomposition reactions involving sulfide oxidation, specific interaction with Fe and Mn oxides, and fermentation (Presley and Kaplan, 1968) occur, but will not be emphasized here. 

Many industrial processes are driven forward by separation of at least one of the reaction products. For many of the reactions in aqueous solutit ns one of the products has low solubility in the reaction medium. Its precipitation or evaporation pushes the reaction forward. If, on the other hand, all the products are soluble, an equilibrium is reached and a means of separation has to be applied to recover the product and to recycle the reagents (shift the equilibrium). The economics of such processes is strongly affected by the concentration of the product at equilibrium, which determines the load on the separation and the cost of concentrating the separated product. This could be the case in many processes such as acid production through displacement from its salts production of water-soluble salts, e.g., fertilizers, through metathetic ( double decomposition ) reactions and product-inhibited fermentation,... 

If oxygen is in low concentrations, it is often the elevated pressure resulting from the rise in temperature in a closed medium that presents a risk (of bursting the autoclave, for example). Further dangers can come from degassing associated with fermentation or decomposition reactions the gas emitted could lead to a rise in pressure (or be inflammable). 

A catalyst is a substance that iacreases the rate of approach to equiUbrium of a chemical reaction without being substantially consumed itself. A catalyst changes the rate but not the equiUbrium of the reaction. This definition is almost the same as that given by Ostwald ia 1895. The term catalysis was coiaed ia ca 1835 by Ber2eHus, who recognized that many seemingly disparate phenomena could be described by a single concept. For example, ferments added ia small amounts were known to make possible the conversion of plant materials iato alcohol and there were numerous examples of both decomposition and synthesis reactions that were apparendy caused by addition of various Hquids or by contact with various soHds. 

Examples of autocatalytic reactions include the decomposition of C2H4I2 either in the gas phase or in solution in CC14 (Arnold and Kistiakowsky, 1933), hydrolysis of an ester, and some microbial fermentation reactions, The first of these may be used to illustrate some observed and mechanistic features. 

Anaerobic. A type of chemical reaction that occurs in the absence of oxygen such as the fermentation of sugars by yeast or decomposition of sewage sludge by microorganisms. 

This type of autocatalytic reaction is a simplification of many biological reactions such as fermentation, where the reaction produces products (species B in the previous example), which accelerates the rate. In fermentation, yeast cells in the solution produce enzymes that catalyze the decomposition of sugar to produce ethanol as a byproduct of yeast reproduction. Since the yeast population increases as the reaction proceeds, the enzyme concentration increases, and the process appears to be autocatalytic. A highly simplified description of fermentation might be... 

DKP Formation in Model Peptide Systems. The fact that DKPs are formed at relatively lov temperatures suggested that catalyzed peptide decomposition occurs in the weakly acidic milieu produced by cacao fermentation. Reactions of simple peptides were followed at 0.02 M (initial concentration) in refluxing acetic acid (120°C) to simulate the interior of a bean during roasting (Table II). 

In summary the methane fermentation of H2 (Reaction 2) is the only example so far which unequivocally uses COo as a methane precursor, and it may be the only methanogenic component in most other substrate decompositions reported as methane fermentations. There are, however, two examples of methane fermentations where the major methane precursor is never COo but an intact methyl group. In the methane fermentations of acetate and methanol, isotopic labels of the methyl groups are transferred without loss or randomization of their hydrogen substituents, to methane ... 

Sakaki T. Shibata M. Miki T. Hirosue H. (1996) Reaction mrxiel of cellulose decomposition in near-critical water and fermentation of products. Bioresource Technol. 58, 197-202. 

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