Tests for the Presence of Starch, Glucose, Protein

Essential Understanding: Digestion in humans involves the break down of food into smaller molecules that can be absorbed into the bloodstream. Various biological tests are used to identify the presence of certain substances - in this context, starch, glucose and proteins.
Starch Test: To test for the presence of starch in a sample, the iodine solution is used. A positive test for starch is when the sample changes from its original colour to a dark blue or black colour in the presence of an iodine solution.
Glucose Test: For detecting glucose, Benedict’s solution is a commonly used reagent. When the solution is heated with a sample that contains glucose, the solution changes its colour from blue to green, yellow, orange or red, based on the quantity of glucose present. The brighter the colour, the more glucose is present, with red indicating a higher glucose concentration.
Protein Test: The Biuret test is used to check for proteins. When Biuret reagent is added to a sample that contains proteins, it changes from a blue colour to a purple colour. If no protein is present, the solution will remain its original blue colour.
In the context of digestion, these tests help understand if the digestive process is functioning properly. For example, after food has been in the stomach, one should not be able to identify large amounts of starch or protein as they should have been broken down by the digestive enzymes into smaller molecules.
Furthermore, they can evaluate the effectiveness of digestive enzymes. Enzymes such as amylase, which breaks down starch into glucose, can be studied to see if they are functioning as they should.
These tests are not definitive and should be supported with other evidence before drawing a final conclusion. Other substances can also cause colour changes. For instance, vitamin C can reduce Benedict’s reagent leading to a false-positive result for glucose.