Introduction to Lab Ex 17 Fermentation of Carbohydrates

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 p. H of the medium. With the inclusion of a p. H indicator in the medium the lowering of the p. H 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 medium.

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 p. H 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 p. H increasing. When a bacterium ferments the sugar and lowers the p. H and depletes all the sugars, the proteins in the medium will then be broken down resulting in alkaline products, which in turn increase the p. H, reversing the results of sugar fermentation. Thus fermentation reactions have to be read within 18 -24 hours before sugar reversion can occur.