Introduction to Lab Ex. 17: Fermentation of Carbohydrates F

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Transcript Introduction to Lab Ex. 17: Fermentation of Carbohydrates F

Introduction to Lab Ex. 17: Fermentation of Carbohydrates
F- tubes
Introduction to Lab Ex. 17 –
Fermentation Of Carbohydrates: F-tubes
Carbohydrates are good sources of energy for organisms.
These compounds, mostly in the form of sugars, are used by
bacteria in a variety of processes.
The most efficient metabolic process to harvest the energy
from sugars is aerobic respiration.
In the absence of aerobic conditions, organisms may be able to
the sugars, though with minimal gain of ATP.
These processes are characterized by the end products.
Organisms are able to metabolize carbohydrates to harvest the
energy in these compounds through metabolic pathways.
The ability of cells to catabolize specific substrates is dependent
on their ability to produce appropriate enzymes.
Catabolic processes primarily include:
aerobic respiration, fermentation
Fermentation is the catabolism of sugars in the absence of oxygen
where the final electron acceptors is an organic molecule.
Fermentation typically results in the formation of organic acids and
alcohols that will accumulate in the medium.
This will result in the lowering of the pH of the medium.
With the inclusion of a pH indicator in the medium the lowering
of the pH can become a visual reaction.
Some bacteria characteristically produce gases during the fermentation
process, which can be made visible by the addition of inverted
tubes in the case of liquid media and cracks in the agar in solid
The ability to ferment specific sugars is dependant on the ability of the
bacterium to produce the specific enzymes required for the
transport and metabolism of that particular sugar.
Thus fermentation of various sugars can be used to characterize bacteria.
The F-tubes use phenol red in the medium as pH indicator and the use
of inverted tubes to detect production of gases.
Results are recorded as Acid/Acid Gas/ Alkaline/ No reaction.
One phenomenon to consider while studying fermentation of sugars
is Protein sparing
Cells will prefer to use sugars for energy when they are present,
sparing the proteins; proteins will be used after the sugars
have been depleted).
Protein sparing can result in the results of sugar fermentation
becoming reversed (sugar reversion).
When protein is metabolized the end products are alkaline in nature
and this will result in the pH increasing.
When a bacterium ferments the sugar and lowers the pH and depletes
all the sugars, the proteins in the medium will then be broken
down resulting in alkaline products, which in turn increase
the pH, reversing the results of sugar fermentation.
Thus fermentation reactions have to be read within 18-24 hours
before sugar reversion can occur.