Food tests

Question 1

Test for starch?

Answer 1

Iodine
Yellow-brown to blue-black

Question 2

Test for lipids?

Answer 2

Emulsion test:
Add ethanol, filter, add to clean test tube, cloudy white emulsion forms

Question 3

Test for proteins?

Answer 3

Biuret:
Light blue to lilac

Question 4

Test for reducing sugars?

Answer 4

Heat (80˚C in water bath) with Benedict’s solution
blue-green -> brick red ppt.

Question 5

Test for non-reducing sugars?

Answer 5

Boil with HCl to hydrolyse the sucrose into glucose and fructose
Cool and neutralise with sodium hydrogencarbonate
Test again w Benedict’s

Question 6

What order do we test for reducing and non-reducing sugars in?

Answer 6

Reducing then non-reducing

Question 7

What’s the weird way they may ask you to test for proteins?

Answer 7

Add NaOH and then CuSO4
(same colour change light blue to lilac)