MODULE 4 - POLYSACCHARIDE

• Iodine test


  Used in testing for starch in a solution, forms coloured complexes
• Iodine solution


  Potassium Iodide + Iodine in water
• Positive iodine test results

  • Black/Blue/Purple
• Negative iodine test results

  • Brown to yellow coloration
• Raw starch


  • Little color change (yellowish to brown)
• Cooked starch


  • Dark blue color (blue-violet)
• Raw + Cooked starch

  1. BEFORE heating - purple/blue solution

  2. AFTER heating - colorless solution
• Glycogen


  • Pale yellow to brown solution
• Cellulose (Filter paper)


  • Pale brown stain that fades away over time
• Starch hydrolysis


  Addition of Water / H2O to the glycosidic bonds, breaking it
• Starch hydrolysis catalysts


  Acids or Enzymes
• Condensation


  The opposite reaction of Hydrolysis, wherein water is released
• Fehling's test


  Used for detecting reducing sugars in a solution
• Fehling's A


  Copper (II) sulphate, blue in color
• Fehling's B


  Potassium sodium tartrate in a strong alkaline solution, clear
• Fehling's solution


  Mix of Fehling's A and B in equal amounts
• Fehling's test procedure


  Add test sample to Fehling's solution, then heat up to 60deg Celsius
• Positive Fehling's test result

  • Orange or Brick-red precipitate
• Negative Fehling's test result

  • Blue solution, no precipitation
• Starch hydrolysis


  Starch > Amylodextrin (violet with iodine) > Erythrodextrin (red with iodine) > Achrodextrin > Maltose > Glucose
• Titration with Phenolphthalein and NaOH

  • Pale pink endpoint, neutral, magenta/darker color means over-shot or over titrated solution
• Fehling's test on hydrolyzed starch

  • Brick-red coloration, red to orange precipitate, positive
• Strong acids/bases


  Corrosive compounds depending on their pH
• Cellulose


  Main component of plant cell walls, provides the molecular/structural foundation for plants
• Untreated paper (Cellulose)


  • Rough, yellow/brown stain with iodine that fades over time
• Treated paper


  • Smooth, weak/pale yellow stain with iodine that fades over time
• Starch solution


  • Dark blue/purple/black coloration upon reaction with iodine