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  Report Class   General Public Report
  Analysis Type   Situation Analysis
  Issue Category   Technology Analysis
  Release Date   03_03_2009
  Last Update  
  Reference Code   GPR-SA.TA.FT-20090303-MUS

Fermentation Technologies
Fermentative Microbial Utilization of Sugars

by Opubo G Benebo


Several types of sugars are defined in the organic chemistry, with the commonly encountered types of sugars being  Glucose, Fructose, Sucrose, Lactose and Mannose, Xylose, Galactose, Arabinose.  The fermentation of these sugars is often performed by microbes, and primarily by two types of microbes: Yeasts of and Bacteria. Each type of sugar is best fermented by a special class of microbe; so in general, the choice of microbes for use in a particular process is determined by the known available substrate - also the sugar - for utilization and the desired end-product of the fermentation. The choice of the microbe necessarily depends on the fermentation reaction characteristic of that microbe.

Fermentation reactions are components of the metabolic reactions occurring within the microbe. All microbial fermentations is merely a reaction subset of the metabolic reactions set or pathway of microbes, performed with the singular object of generating energy bond substances and the use of such substances for the conduct of cell maintenance facilities. The metabolic processes usually are of two types: Anabolism and Catabolism; and the catabolic reactions are the reaction subset that generate the energy bond substances while the anabolic reactions are the consumer of such substances.

Of course, the specificity of microbe requirement implies that when the substrate, or "Mash" is a mixture of sugars, then the microbe must also be of a mixture of microbe-classes.  However, except for optimization mix designs, the Mash for all fermentation processes, are somewhat similar, being a mixture of the substrates as reactants for the catabolic reactions and additional substances as catalysts or reactants for the anabolic reactions. Obviously optimized Mash composition would be different for each microbe given that even within the same type of microbe, each strain will have a slightly different metabolic reaction and consequently generate a different product mix for the fermentation, at least in terms of final concentrations.

Notably, many strains  of microbes of the same genus or class can perform the fermentative utilization of the the same substrate : There are about eleven (11) strains of S. cerevisiae that ferment glucose, and there are about seventy-two (72) strains Kluyveromyces Marxianus that ferment lactose; and given the uniqueness of each strain, it is entirely plausible to presume that  each one possibly has a slightly different set of metabolic reactions and consequently will generate a different product mix for the fermentation of the same substrate and Mash composition. The perspective immediately presents that  the microbe type whether yeast or bacteria, itself can suffer variation depending on the type of alcohol-product desired.


Rationally then, the first task therefore is the cataloguing of the metabolic reactions in terms of product mix  against fermentative microbes. This  should allow for a process of rational selection of microbes and combinations of microbes to achieve very special types of fermentation reactions. Even then, this proposed cataloguing is better conducted with respect to each class of microbes that ferment specific sugar type, for the purposes of generating the microbes selection guide catalogue.

The Biochemical Pathways
Metabolic reactions occur inside the cytoplasm of the microbes. In the microbial cytoplasm, the substrate is first prepped for use in the respiratory exergonic process required to support the anabolic reaction which are endogornic.

The prepping process may be phosphorylative and or nonphosphorylative, the former being the more common. Phosphorylative reactions are the catabolic reactions in which Phosphate ions of the ADP are catalytically transferred to a glucose molecule to form glucose 6-phosphate.  The prepping of galactose, however, begins with the converting of galactose into glucose-1-phospate within the Biochemical Pathway, and this process of the fermentative utilization of galactose seem to follow either one of two Biochemical Pathways : The d-galactose (tagatose) -6-phosphate, and The Leloir Pathway;  further the path by which the metabolic conversion of galactose is started determines the results of the end-products. The completion of the phosphorylation marks the beginning of the catabolic reactions, commonly known as glycolysis, and ending with the fermentation reaction that is the reoxidation of pyruvate into alcohol and other by-products.

The mechanism of the catabolic reactions involving fermentation, often termed biochemical pathway, however, is dependent on the microbe and the substances mix. Generally the pathway entails the degrading of the glucose 6-phosphate to pyruvate followed by the glucose metabolism leading to ethanol fermentation which has been studies extensively over the years: Generally, the metabolic reactions occur beginning with the catabolic reactions, which produce products such as the ATP that are then used in the anabolic reactions.

In the case of yeast the catabolic reaction often entails the oxidation of substrate which is often an organic sugar.  The metabolic reaction - or fermentation reaction - begins with the processing of glucose primarily by way of the Embden-Meyerhoff pathway followed by the biochemical fermentation reaction.

In the case of bacterium the catabolic reaction often entails the oxidation of substrate which is often an organic sugar; and the metabolic reaction including

 

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the fermentation reaction begins with the processing of glucose primarily by way of the Entner?Deudoroff pathway followed by  the fermentation reaction to produce ethanol and possibly carbon dioxide as by-product.

On the basis of all these, then the fermentation of alcohol may now be substantively defined as the consumption of [organic] sugar by microbes with the production of alcohol. The importance of the qualifier "organic" can not be over over-emphasized, because it has a bearing on the choice of the yeast.

Equally, noteworthy is that the conversion of the sugar of any type into any alcohol is also never 100 percent, because of the need to partly utilize some nutrients in synthesizing new biomass and other cell maintenance related reactions; and the actual extent of conversion depends on the type of microbe, and on the type of sugar.


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