Food Tests.

Question 1

How to test for reducing sugars:

Answer 1

Add about 2cm cubed of test solution (e.g. glucose), add an equal amount of Benedict’s solution in a test tube, heat it in a water bath for a few minutes, then look at the change in colour- it will now be brick-red.

Question 2

How to test for starch:

Answer 2

Add iodine solution using a pipette 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.

Question 3

How to test for proteins:

Answer 3

Add 1 cm3 of biuret solution A to the food solution.
Mix the liquids.
Add 1 cm3 of biuret solution B and shake the test tube as to form two layers.
A purple colour indicates protein is present.

Question 4

How to test for lipids using the Sudan III test?

Answer 4

Equal amounts of food and water are added to a test tube.
Drops of Sudan III are added and the test tube is shaken.
A red-stained layer forms on the surface of the water if lipids are present.

Question 5

How does the emulsion test work?

Answer 5

Ethanol is added to a test tube containing crushed food.
The liquid is poured into a second test tube containing water, leaving any food residue behind.
A cloudy liquid (or emulsion) indicates the presence of lipid in the food.