chapter 2

2.1 Testing for Biological Molecules

How to Carry Out the Tests

1. Benedict’s Test for Reducing Sugars:

   • Procedure:

     • Dissolve the sample in water and add an equal volume of Benedict's reagent.

     • Heat the mixture in a boiling water bath for about 5 minutes.

   • Observation: A color change from blue to green, yellow, or brick-red indicates the presence of reducing sugars, depending on the concentration.

2. Iodine Test for Starch:

   • Procedure:

     • Add a few drops of iodine solution to the sample.

   • Observation: A blue-black coloration indicates the presence of starch.

3. Emulsion Test for Lipids:

   • Procedure:

     • Mix the sample with ethanol to dissolve any lipids and then add water.

   • Observation: A milky emulsion indicates the presence of lipids.

4. Biuret Test for Proteins:

   • Procedure:

     • Add Biuret reagent (sodium hydroxide and copper sulfate) to the sample.

   • Observation: A violet coloration indicates the presence of proteins.

5. Semi-Quantitative Benedict’s Test:

   • Procedure:

     • Conduct the standard Benedict's test and record the time to first color change or compare to a series of color standards.

   • Estimation: Use the results to estimate the concentration of reducing sugars in the sample based on the intensity of color change.

6. Test for Non-Reducing Sugars:

   • Procedure:

     • Boil the sample with dilute hydrochloric acid to hydrolyze non-reducing sugars into reducing sugars.

     • Neutralize the solution with sodium hydroxide and then perform the Benedict’s test.

   • Observation: A positive result (color change in Benedict’s test) after hydrolysis indicates the presence of non-reducing sugars.