The Uses, Principle And Procedures Behind The Starch Hydrolysis Test

Many of the scientific tests that are carried out by researchers and scientists every day can feel somewhat unintelligible (somewhat ironically), especially for newcomers to the field, or if you simply haven’t kept up on the latest news regarding bacterial studies.

The Uses, Principle And Procedures Behind The Starch Hydrolysis Test

However, these tests are vital to furthering our understanding of how these pathogens operate, as well as making these bacteria identifiable for patients that need answers to their conditions. As such, it is not exactly like they can just be brushed over.

However, when the process is broken down into its core stages and phases, understanding becomes much easier to grasp. 

This is what we are hoping to help resolve in this short piece! We are going to break down the purpose, the procedure, and the principles behind one of these many tests that are carried out in laboratories, the Starch Hydrolysis test.

The Purposes And Objective Of The Starch Hydrolysis Test

So, before we go any further into this article, we should probably first explain what exactly it is that the Starch Hydrolysis test’s objectives are, and what is used for.

To put it simply, the Starch Hydrolysis test is a procedure that will help a researcher determine whether or not any organisms contained in the sample that is being tested can hydrolyze starch in some way, which is considered proof that an organism is capable of producing the enzyme amylase, which is essential for release during digesting carbohydrates for an organism.

This is an enzyme that most bacteria and fungi can produce, and can be differentiated depending on what form of amylase is produced in the starch hydrolyzation process.

Principle Behind The Starch Hydrolysis Test

So, we now know that the test is effectively searching for the presence of amylase that is caused by hydrolyzing starch. But how exactly does this test tell us this information? What is the principle that scientists use to read and understand this test?

Well, generally speaking, starch is a complex carbohydrate nutrient that is usually too large to simply pass through a cell wall and be digested. So, for it to be used in energy production, it must be broken down to be absorbed through the membrane of a cell.

So, bacteria that are tested are grown in an agar medium plate that will contain starch. In the cases where the bacteria can hydrolyze the starch, it will starch grow across the medium it is being grown in.

However, the result of this bacterial growth isn’t easily spotted by the naked eye without staining. So, after an appropriate incubation period has happened, iodine is then added to the medium to indicate the culture’s growth.

Once the iodine has been added, areas with hydrolyzed starch will remain the color that they were previously, while areas with non-hydrolyzed starch will turn a dark blue color.

As a result of the technique of applying the bacteria culture in the agar medium, the bacteria colonies will often form clear trails around where they have grown after iodine has been added.

How To Carry Out The Procedure For The Starch Hydrolysis Test

So, now that we have an idea of how the test samples should react when carried out, it is time to show you how to do it for yourself.

  • Using some type of sterilized technique or implement, make a single stroke of your bacteria culture across the prepared agar plate. Make sure that this plate is labeled, so that it isn’t lost or confused with another during the testing process.
  • Make sure that the bacteria plates are kept in a secure and regulated place for 48 hours, with the temperature being set to 37 degrees Celsius (98.6 degrees Fahrenheit)
  • Once the incubation period has finished, make sure to flood the surface of the agar medium with your iodine solution for 30 seconds. It is recommended that you apply the iodine with a dropper for the most control and accuracy.
  • Pour off any excess iodine that is on your agar plate.
  • With the excess iodine gone, you can now measure the results for yourself.

As you can see, while the results can take a while to become clear, the procedure is very simple.

Result Interpretation

As we have already mentioned, there are two main results that you should expect from this test:

  • Any bacteria that can and have successfully hydrolyzed the starch will result in a clear outline from the rest of the iodine solution and can be counted as a positive result.
  • Any spots of iodine that are black, purple, or blue after the iodine is added will indicate non-hydrolyzed starch and are considered a negative result.

Other Notes To Keep In Mind

There are a few things to consider when looking at the results of this test:

  • The color of the iodine will only be affected by its concentration, so do not be concerned if a light purple is the result of a negative test.
  • Whilst this is an effective preliminary test, a pure culture should require further testing for a more precise result.
  • The culture that is grown will start to die after the iodine is applied, thanks to the oxidation from the iodine.


As you can see, this is a simple, yet clear test for researchers to try in laboratories. And now, you understand those results too.

Jennifer Dawkins

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