Biomolecules & food tests

• Biomolecules structures

  • Carbohydrates/polysaccharides - Monosaccharides
  • Proteins/polypeptides - Amino acids
  • Fats/lipids/triglycerides - 1 glycerol + 3 fatty acids
• Biomolecules bonds

  • Carbohydrates - Glycosidic bond
  • Proteins - Peptide bond
  • Lipids - Ester bond
• Food tests

  1. Starch-iodide test: test for starch
  2. Biuret test: test for proteins
  3. Benedict's test: test for reducing sugars
  4. Ethanol emulsion test: test for lipids
• Starch-iodide test

  1. Add one drop of iodine solution on white tile followed by one drop of test solution and mix well

  Mixture turned from yellowish-orange to blue-black

  Mixture remained yellowish-orange
• Biuret test

  1. Add 1.0cm of test solution to a clean dry test tube
  2. Add 1.0cm of Biuret reagent to test solution
  3. Shake well to mix and observe colour change

  Mixture turned from blue to lilac: protein is present

  Mixture remained blue: protein is absent
• Benedict’s test

  1. Add 1.0cm of test solution to a clean dry test tube
  2. Add 1.0cm of Benedict’s solution to test tube and swirl
  3. Leave test tube in a boiling water bath for 3 minutes
  4. Observe for formation of ppt

  Brick red/orange/yellow/green ppt was obtained from a blue mixture: Large/moderate/low/trace amount of reducing sugar
• Ethanol emulsion test

  1. Add 2cm of ethanol to two drops of test solution in a test tube. Mix well and allow to stand for 2 min
  2. Decant ethanol into another test tube with 2cm of water, mix well

  White emulsion was formed when water was added: Lipids are present

  Mixture remained clear when water was added: Lipids are absent