food tests

Question 1

reducing sugar

Answer 1

• heat sample in equal vol of benedicts reagent

positive result:
blue –> orange/brick-red

Question 2

non-reducing sugar

Answer 2

negative result from reducing test
- add HCl to hydrolyse + boil
- cool + neutralise w alkali (sodium hydrogen carbonate)
- heat in benedicts

positive result:
blue –> orange/brick-red

Question 3

starch

Answer 3

• add 2 drops of iodine to sample

positive result:
orange –> blue/black

Question 4

lipids

Answer 4

• dissolve sample in ethanol by shaking
• add distilled water

positive result:
milky white emulsion

Question 5

proteins

Answer 5

• add biuret solution to sample
  (consists of sodium hydroxide + copper (II) sulfate)

positive result:
blue –> purple