food tests

Question 1

test for starch

Answer 1

Iodine test for starch:

1.Add few drops of iodine solution to test tube containing some prepared food sample.

2.Gently shake the test tube to mix.

3.Observe any colour changes.
The brown-orange solution will turn blue-black in the presence of starch.

Question 2

test for proteins:

Answer 2

biuret test-
1)Add few drops of biuret A and biuret B to test tube containing some of prepared food sample.

2)Shake test tube gently to mix.

3)Look for any colour changes.
If protein is present, solution will change from blue to purple.

Question 3

test for reducing sugar

Answer 3

Benedict’s test for reducing sugars:

-Add few drops of Benedict’s solution to a test tube containing some of the prepared food sample.

-Put test tube in a water bath at
80°c for 5 mins

-take note of any colour change.
The blue Benedict’s solution will turn green, yellow or brick red solution contain reducing sugar. colour it changes to will depend on how much sugar there is in the food.

Question 4

Sudan test for lipids

Answer 4

Sudan III test for lipids:

-Add few drops of Sudan III stain to a test tube containing the prepared food sample.

-Shake the test tube gently.

-Observe any changes in the test tube.
If a lipid is present, the solution will separate into 2 layers. The top layer will be the lipid and will be stained red by the Sudan III stain.

Question 5

emulsion test for lipids

Answer 5

Emulsion test for lipids:

-Add a few drops of ethanol and a few drops of distilled water to a test tube containing the prepared food sample.

-Shake gently to mix the contents of the test tube.

-Observe any changes.
If a lipid is present in the sample, the colourless solution will turn into a cloudy white emulsion.