Biochemical tests

Question 1

Describe the chemical test for lipids

Answer 1

• Add ethanol/ alcohol to food sample and shake
• Or dissolve the food sample in ethanol/alcohol and shake
•Add distilled water and shake gently
• If a white/milky/cloudy emulsion is formed then the reaction is positive

Question 2

Describe the test for proteins

Answer 2

• Solution must be alkaline
• Add copper (II) sulphate
• Add biurets to food sample
• If food sample turns from blue to purple then the reaction is positive
• It is a protein

Question 3

Describe the test for starch

Answer 3

• Add iodine dissolved in potassium iodide to the food sample
• Wait for the solution to turn from orange to blue black then the reaction is positive
• The food sample contains starch

Question 4

Describe the reducing sugars test

Answer 4

• Add Benedict’s reagent to food sample
• Heat in a water bath that has been brought to boil
• Wait for five minutes till color
changes from blue to brick red for the reaction to be positive
• If so the food sample is a reducing sugar

Question 5

Describe the non-reducing sugars test

Answer 5

• Following the negative Benedict’s test
• Add an acid ( HCL )to hydrolyze the bonds
• Add an Alkali ( NaOH) to neutralize the acids
• Add Benedict’s reagent
• Heat in a water bath that has been brought to boil
• Wait for five minutes
• If the food sample turns from blue to brick red then the reaction is positive
• It is a reducing sugar