CARBS - SUMMARY

• the molisch test is the general test for carbohydrates
• a negative result of molisch test indicates absence of carbs
• Tests based on the formation of furfural and its derivatives

  • molisch
  • seliwanoff
  • bial's orcinol

  based on reducing property of sugar

  • benedict's
  • barfoed's

  hydrolysis of disaccharides and polysaccharides

  • sucrose
  • starch
• benedict - brick red precipitate

  barfoed - brick red

  seliwanoff - cherry red

  molisch - purple or violet ring

  bial - blue or green

  iodine - blue black or pale brown to highly branched polysacc
• benedict

  • non reducing - (clear blue)
  • starch
  • sucrose
  • reducing +(brick red precipitate)
  • galactose
  • pentose
  • glucose
  • fructose
  • lactose
  • maltose
• iodine test

  • colorless
  • sucrose
  • + blue-black
  • starch
• barfoed

  • negative - lactose and maltose
  • positive (brick red) - galactose, glucose, pentose, fructose
• bial orcinol

  • negative (brown) - galactose and glucose
  • positive (blue) - fructose
• seliwanoff

  • negative (no color) - galactose and glucose
  • positive (cherry red) - fructose
• presence

  molisch - carbs

  seliwanoff - ketohexoses like fructose; indicates the presence of ketoses

  benedict - reducing sugar like glucose and fructose

  barfoed - monosaccharides

  bial - ribose

  iodine - starch
• compound reaction

  molisch - a naphtol - furfural with hydroxymethylfurfural

  seliwanoff - recorcinol - dehydrated ketohexose

  benedict - copper sulfate III - aldehyde

  barfoed - cupric ion - oxidation reduction reaction

  bial - orcinol/ferric ions - furfural (pentose) and hydroxymethylfurfural

  iodine - polyiodide ion - amylae and amylopectin
• materials

  1. Test tube
  2. Aspirator
  3. Pipette
  4. Cotton balls
  5. Watch glass
  6. Water bath
  7. 250 mL beaker
  8. Dropper
  9. Spot plate
• reagents

  1. Distilled H2O
  2. 3% solution of glucose, xylose
  3. Fructose, lactose, sucrose, starch
  4. Molisch reagent
  5. Bial’s orcinol
  6. Barfoed’s
  7. Iodine solution
  8. H2SO4
  9. HCL
  10. 0.1 N NaOH
  11. 6 N HCl
  12. Sodium carbonate test solution
• molish

  • purple ring