BIOCHEMISTRY PRACTICAL TESTS

Explaining what tests to use and how to do them, testing for starch, reducing sugars, non-reducing sugars, lipids and proteins.

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Practical Biochemistry Tests ­ LEARN
STARCH:
Add a solution of iodine to sample
If starch is present, iodine changes colour from yellow-brown to blue-black
REDUCING SUGARS:
Add Benedicts solution (alkaline copper sulphate) to sample
Heat in a water bath of 80oc
If reducing sugar is present it turns brick-red ­ if not present no change
Compare sample to know sugar contents in a colorimeter
If not present ­ do non-reducing sugar test
If present ­ compare on a graph to the know sugar contents solutions
NON-REDUCING SUGARS:
Make sure no reducing sugars in sample
Boil the sample with Hydrochloric acid
Cool solution and neutralise by adding sodium hydrogen carbonate solution
Repeat reducing sugar test again
BIURET TEST (TESTING FOR PROTEINS):
Add biuret reagent to sample
If colour changes to lilac proteins are present
ETHANOL EMULSION TEST (TESTING FOR LIPIDS):
Mix sample with ethanol ­ dissolves any present lipid
Then pour liquid into water contained in another clean test tube
If lipid present ­ cloudy white emulsion with form near top of water
Testing For Description Result (colour change)
Starch Add a few drops of iodine Brown to blue/black
solution
Reducing sugar Add Benedict's solution and Blue to brick-red
heat to 80oc in water bath
Non-reducing sugar If reducing sugar test is ­ve, Blue to brick-red
boil with HCL acid, cool and
neutralise with sodium
hydrogencarbonate solution;
repeat Benedicts test
Protein Add biuret reagent Blue to lilac
Lipid Add ethanol to extract lipid White emulsion forms near
and pour alcohol into water top of water
in another test tube

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