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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.
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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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