Biological Molecules 5 - Biological Food Tests

Question 1

Describe the food test for proteins

Answer 1

test for soluble proteins is called a biuret test
few drops of biuret reagent are added to protein soln.
shake gently
soln. turns from light blue to purple/lilac colour
no colour change observed if no protein

Question 2

What is the food test for reducing sugars?

Answer 2

add to test tube your test sample and benedict’s reagent
boil in a water bath
pos. result: light blue soln. turns brick red
neg. result: no colour change observed

Question 3

What is the food test for non-reducing sugars like sucrose?

Answer 3

add HCl to test sample and boil
any glycosidic bonds will be hydrolysed
add hydrogen carbonate powder to neutralise
add benedict’s reagent and boil
same results as reducing sugar can be shown but pos. result means sucrose is present

Question 4

Describe the food test for starch.

Answer 4

iodine soln. turns from orange-brown to blue-black in presence of starch
qualitative test

Question 5

Describe food test for lipids.

Answer 5

mix test sample with equal vol. of ethanol to dissolve lipids
add equal vol. of H20
shake gently
white and cloudy soln. forms