3.4 Testing for carbohydrates

Question 1

What solution is used to test for carbohydrates (sugars)

Answer 1

Benedict’s solution (copper sulphate)

Question 2

Benedict’s test steps

Answer 2

Add 2cm^3 of food sample (liquid form)
Add equal amount of Benedict’s reagent
Heat mixture gently in water bath for 5 mins

Question 3

Results in benedict’s test for reducing sugars

Answer 3

Reducing sugars react with blue Cu2+ ions in benedict’s
form a red precipitate (brick red)

Question 4

Method for benedict’s test for non-reducing sugars

Answer 4

Must first be hydrolysed into its monosaccharide components
- first test with benedicts

Question 5

If there is no colour change with non-reducing sugars…

Answer 5

Add HCl
Heat in water bath for 5 mins
Add alkali sodium hydrogen carbonate and indicator until neutralised
Then reconduct benedict’s test

Question 6

Example of reducing sugar

Answer 6

Glucose

Question 7

Example of non-reducing sugar

Answer 7

Sucrose