Food tests

Question 1

Describe the benedict’s test for reducing sugars

Answer 1

Add an equal volume of the sample being tested and benedict’s reagent
Heat the mixture in an electric water bath at 100 degrees for 5 minutes
Observe the colour of the precipitate formed

Question 2

Describe the positive result for reducing sugars

Answer 2

Colour change from green/yellow to orange/brown/brick red
Depends on the quantity of reducing sugar present

Question 3

Describe the benedict’s test for non-reducing sugars

Answer 3

Negative test for reducing sugar
Hydrolyse non-reducing sugars with an equal volume of dilute HCl
Heat in a boiling water bath for 5 minutes
Add NAHCO3 to neutralise the acid
Re-test resulting solution with benedict’s reagent
Observe the colour of the precipitate formed

Question 4

Describe the positive result for non-reducing sugars

Answer 4

Colour change from green/yellow to orange/brown/brick red
Depends on the quantity of non-reducing sugar present

Question 5

Name the food test used to identify proteins

Answer 5

Biuret test

Question 6

Describe the biuret test

Answer 6

Add an equal volume of the sample to be tested and NaOH
Add a few drops of dilute copper (II) sulfate solution
Mix gently and record any observations

Question 7

Describe the positive result of a biuret test

Answer 7

Colour change from pale blue to purple

Question 8

Describe the iodine-potassium iodide test and colour change for starch

Answer 8

Add iodine-Kl solution
Colour change from orange to blue-black in the presence of starch

Question 9

Describe the emulsion test for fats and oils

Answer 9

Add ethanol to the sample and shake
Allow the mixture to settle
Add an equal volume of water
Record any observations

Question 10

Describe the positive result of an emulsion test

Answer 10

White, cloudy emulsion forms