Required practical 4

Question 1

Describe the method of preparing a food sample before testing.

Answer 1

1. Take food sample and grind this with distilled water using a mortar and a plate. This should make a paste.
2. Transfer paste to a beaker and add more distilled water. Stir so chemicals in food dissolve in water
3. Filter solution to remove suspended food particles.

Question 2

How do you test for starch ?

Answer 2

• Add 2cm^3 of food solution into a test tube
• add a few drops of iodine solution
• if present will turn from orange to blue / black

Question 3

How do u test for sugars ?

Answer 3

• Place 2cm^3 of food solution into test tube
• add 10 drops of Benedict solution
• Place test tube into beaker half filled with hot water
• leave for 5 mins

Question 4

What does the sugar test show as results ?

Answer 4

Green = small amount of sugar is present
Yellow = more sugar present
Brick Red = lots of sugar is present

Question 5

How do you test for protein ?

Answer 5

1. 2cm^3 of food solution
2. add 2cm^3 of buiret solution
3. will turn from blue to purple/lilac if present

Question 6

How do you test for lipids ?

Answer 6

! don’t filter the solution as lipid molecules can stick to paper !

1. add 2cm^3 of lipid solution to test tube
2. add few drops of distilled water and ethanol
3. Gently shake solution
4. if present a cloud of white emulsion forms
   - Ethanol is flammable and therefore no flames should be near.