Food Testing

Question 1

Reducing sugars (eg glucose, fructose, maltose)

Answer 1

Regent used to test = Benedict’s
Method= Add 2cm3 of Benedict’s an equal amount of the test sample, heat over water bath
Starting colour= Blue
End Colour= Orange/Red precipitate

Question 2

Non-Reducing sugar (sucrose)

Answer 2

Reagent used to test= Benedict’s, HCL and NaHCO3
Method= 1. Boil test sample with HCL (breaks glycosidic bonds)
2. Neutralise with NaHCO3/alkali (otherwise the HCL would react with the Benedict’s solution).
3. Add Benedict’s solution to test sample, heat over water bath
Starting colour= Blue
End Colour= Orange/Red Precipitate

Question 3

Starch

Answer 3

Reagent= Iodine Solution
Method= Add a few drops of iodine solution to test sample
Staring colour= Yellow/Brown
End colour= Blue-Black

Question 4

Lipids

Answer 4

Reagent used= Emulsion Test (ethanol and water)
Method= 1. Shake some of the test sample with about 4cm3 of ethanol.
2. Decant the liquid into a test tube of water, leaving any undissolved substances behind
Starting colour= Clear
End Colour= Formation of a cloudy white emulsion

Question 5

Proteins

Answer 5

Reagent used= Biuret Reagent
Method= Add a few drops of Biuret Regant to the test sample
Starting Colour= Blue
End Colour= Lilac/Purple precipitate

Question 6

Cellulose

Answer 6

Reagent used= Schultze’s solution
Method= Add a few drops of Schuktze’s solution to test sample
Starting Colour= Yellow
End Colour= Purple