Method:
(For reducing sugars)
Add the sample of apple into a test tube, add a few drops of Benedicts solution into the sample, then, place the test tube into a beaker half full with water, wait until the water boils and observe.
(For starch)
Add a sample of the potato into the test tube, then, add a few drops of iodine solution and observe the color change.
(For lipids)
Add a few drops of oil into the test tube, then, add an equal amount of absolute ethanol, shake vigorously then add an equal amount of water and observe.
(For proteins)
Add a sample of egg yolk into the test tube, then add a few drops of biuret solution and observe.
Results:
Discussion:
In the reducing sugar test, the solution turned red-brown. This is because, as the name suggests, reducing sugar reduced the copper (II) ions in the Benedicts solution into insoluble copper (II) oxide which is seen as a precipitate.
In the starch test, the result was a blue/black color formed in the surface of the potato, this was because the polyiodide complex was formed with starch.
In the lipid test, the result was a milky white solution, this is because lipids do not dissolve in water but do dissolve in alcohols. Hence, an emulsion of tiny droplets of water reflects light and results in a white solution.
In the protein test, the result was a purple solution, this is because peptide bonds are present which form a purple color with copper(II) ions.
Evaluation:
In these experiments, I tried to make it as accurate as possible by doing the following:
- Adding equal amounts of food samples and solutions
However, the experiment could have been better if I:
- Used a different pipette for each solution as the different solutions might have mixed inside the pipette.
Conclusion:
After doing this experiment, I can conclude that egg yolk mostly consists of proteins, apples mostly contain reducing sugars, potatoes are mostly starch, and cooking oil mostly contains fats.
