What Sugars Give A Positive Fermentation Test?


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Rosie Normanton Profile
Rosie Normanton answered
It is suggested that all sugars will give off a positive result through a fermentation test except for amylose and amylopectin. Other than that, all of the following sugars should give off a positive result to the test:

  • Fructose
  • Sucrose
  • Lactose
  • Glucose
  • Galactose
  • Maltose

The fermentation test employs the use of phenol red brother in order to establish what sort of fermentation each sugar has. The results of the test can be observed by the change of color that the brother demonstrates.

If there is an adverse level of acidity then the broth is expected to change to a yellow color. Alternatively, if there is a high level of alkalinity in the carbohydrates then the color of the broth should turn to pink.

When setting up the experiment, make sure that you have labeled each tube appropriately. This is because all the sugars will look the same once you have set them all up in their individual tubes.

Then you will need to insert the bacteria into the tube and allow it to settle in the tube rack. Then take the tube rack full of tubes and incubate them for around a day at a temperature of 37 degrees C. If the bacteria you are using is known for slow growth, extend the amount of time for incubation another day.

Once the waiting is over you can begin to compare the colors of the sugars in the tubes. This will then tell you which sugars emitted excess acidity and which sugars emitted excess alkalinity.

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