Tests

Question 1

Test for starch

Answer 1

1. Add 2cm3 of food sample into test tube
2. Add 2 drops of iodine solution
3. Blue-black colour indicates starch is present

Question 2

Benedict’s test for reducing sugar

all monosaccharides + maltose+ lactose

Answer 2

1. Add 2cm3 of food sample into test tube
2. Add 2cm3 of Benedict’s reagent
3. Heat mixture in a boiling water bath for 5 mins
4. Observe colour change (ROYGB)

Question 3

Benedict’s test for non reducing sugar

sucrose

Answer 3

1. Boil 2cm3 of food sample with hydrochloric acid
2. To hydrolyse disaccharide into 2 monosaccharides
3. Let solution cool and add sodium hydrogen carbonate to neutralise it
4. Add Benedict’s reagent and heat in water bath
5. Observe colour change

Question 4

Emulsion test for lipids

Answer 4

1. Add 2cm3 of food sample into dry grease free test tube
2. Add 5cm3 of ethanol + shake thoroughly
3. Add 5cm3 of water + shake gently
4. Cloudy white sol/ppt indicates lipid is present

Question 5

Buiret test for proteins

Answer 5

1. Add 2cm3 of food sample into test tube
2. Add 2cm3 of sodium hydroxide solution at room temp
3. Add few drops of v. dilute copper (ll) sulfate solution
4. Observe colour change
   (turns from blue to purple, indicates peptide bond is
   present, hence a protein)