Biochemical tests

Question 1

what is a reducing sugar?

Answer 1

Any sugar that can act as a reducing agent because of its aldehyde or ketone group

Question 2

The test for reducing sugars

Answer 2

If the sugar you are testing is a reducing sugar; it will change colour from blue to green/yellow/orange/brick red, depending on the concentration of sugar you are testing.

Question 3

Test for non-reducing sugars

Answer 3

You need to break down the sample into monosaccharides using hydrochloric acid which breaks the glycosidic bonds. The sample is then neutralised with sodium hydrogen carbonate and the Benedict’s test can be carried out. Since sucrose will have been broken down into glucose and fructose, you should now see a positive result.

Question 4

Test for starch

Answer 4

You need to add iodine dissolved in potassium iodide solution. A positive result occurs when the solution changes colour from orange/brown to blue/black.

Question 5

Test for proteins

Answer 5

The Biuret test involves adding sodium hydroxide to a sample followed by copper sulfYr solution. A colour change from blue to purple indicates a positive result.

Question 6

Test for lipids

Answer 6

Add ethanol to a sample and mix thoroughly by shaking. Add an equal amount of water and if lipid is present a milky white suspension should form.