Biochemical tests

Question 1

How would you test for the presence of starch?

Answer 1

Add iodine in the sample, colour change will go from orange to blue/black

Question 2

How would you test for reducing sugars?

Answer 2

Add Benedict’s reagent to the sample and heat, colour change will go from blue to green, yellow, orange or brick red (the more red the higher the concentration of reducing sugars)

Question 3

How would you test for non-reducing sugars?

Answer 3

Do the Benedict’s test for reducing sugars to gain a negative result (blue in colour)

Then add acid and boil for 2 mins to let acid hydrolysis take place

Cool the solution by adding it to a cold beaker and add an alkali to neutralise it

Add the Benedict’s reagent and heat, colour change will go from blue to green, yellow, orange or brick red

Question 4

How would you test for proteins?

Answer 4

Biuret test
- Add equal volume of sodium hydroxide to the sample at room temperature.
- Add drops of dilute copper (II) sulfate solution and swirl to mix.
- Positive result is a color change from blue to purple.

Question 4

Name all the reducing and non-reducing sugars

Answer 4

Reducing:
- glucose
- fructose
- galactose
- lactose
- maltose

Non-reducing
- sucrose

Question 5

How would you test for lipids?

Answer 5

Add ethanol to the sample and shake
Add distilled water and shake again
White emulsion will form if lipids are present.