Use qualitative reagents to test for a range of carbohydrates, lipids and proteins
There are several qualitative tests for food chemicals. These can be used to detect the presence of food chemicals but not how much is present.
It may go through stages - green, yellow, orange, red or brown - depending on how much glucose is present.
Sugars classed as reducing sugars will react with Benedict's solution on heating for a few minutes. Glucose is an example of a reducing sugar.
Reducing sugars give a red/brown precipitate with Benedict's solution. The precipitate takes a while to settle in the tube. The colour you’ll see is likely to be simply red or brown. If there's not much glucose present, the final colour may be green or yellow, or orange if there's a little more.
Add iodine solution to the food being tested.
Foods containing starch will turn a blue-black colour.
The iodine test can also be used with a microscope to stain starch grains in plant cells.
The biuret test is used to detect proteins.
Biuret reagent is available as a single solution.