EXPERIMENT

• Carbohydrates


  Biomolecules composed of carbon, hydrogen and oxygen atoms whose functional group can either be aldehyde or ketone
• Classification of Carbohydrates


  • Monosaccharide
  • Disaccharide
  • Oligosaccharide
  • Polysaccharide
• Monosaccharides


  Simple sugars that could not be hydrolyzed further into smaller units
• Monosaccharides


  • Fructose
  • Glucose

  
• Disaccharides


  Sugars that have two monosaccharide units
• Disaccharides


  • Sucrose
  • Lactose

  
• Polysaccharides


  Sugars that have many monosaccharide units linked together by glycosidic bonds

  
• Polysaccharides


  • Starch
  • Glycogen

  
• Types of Starch


  • Amylose
  • Amylopectin

  
• Aldoses


  Contain aldehyde functional group
• Aldoses


  • Glucose

  
• Ketoses


  Contain ketone functional group
• Ketoses


  • Fructose

  
• Pyranose


  Six-membered cyclic ring
• Pyranose


  • Glucose

  
• Furanose


  Five-membered cyclic ring
• Furanose


  • Fructose

  
• Reducing Sugars


  Can act as reducing agents, have free anomeric carbon or contain free aldehyde or ketone groups
• Reducing Sugars


  • All monosaccharides (glucose & fructose), disaccharide lactose

  
• Nonreducing Sugars


  Cannot act as reducing agents, have no free anomeric carbon or free aldehyde or ketone group
• Nonreducing Sugars


  • Sucrose, starch, glycogen

  
• Moore's Test


  1. Test for reducing sugars

  2. Principle: Reducing sugar undergoes aldol condensation (caramelization reaction) under alkaline/basic conditions because of the free anomeric carbon

  3. Positive result: Caramel odor and brown-yellowish colored complex

  4. Positive for: glucose, fructose, lactose

  5. Negative for: glycogen, sucrose and starch

  
• Theoretical Results for Moore's Test


  Positive for glucose, fructose & lactose

  Negative for sucrose, glycogen, starch

  
• Experimental Results for Moore's Test


  Positive for glucose, fructose & lactose

  Negative for sucrose, glycogen, starch

  
• Barfoed's Test


  1. Test for monosaccharides

  2. Principle: Strong reducing sugars like monosaccharides are oxidized by copper ion in acetic acid solution to carboxylic acid and form Cu2O precipitate within 3 minutes

  3. Positive result: Brick red precipitate

  4. Reducing disaccharides undergo same reaction but at slower rate

  
• Theoretical Results for Barfoed's Test


  Positive for glucose, fructose, lactose (very slow formation of brick red precipitate)

  Negative for sucrose, glycogen, starch

  
• Experimental Results for Barfoed's Test


  Positive for glucose, fructose, lactose (very slow formation of brick red precipitate)

  Negative for sucrose, glycogen, starch

  
• Bial's Orcinol Test


  1. Test for furanose or pentoses (can only distinguish between pentose & hexose sugar)

  2. Principle: Bial's reagent dehydrates pentoses to form furfural and hydroxyfurfural (hexoses) which yields blue green compound in presence of Fe3+ ions

  3. Positive result for Furanoses/Pentoses: bluish-green solution

  4. Hexoses give yellow brown solution (negative result)

  
• Theoretical Results for Bial's Orcinol Test


  Yellow brown solution (negative) for fructose, glucose (hexoses)

  Negative for sucrose, lactose, glycogen & starch

  
• Experimental Results for Bial's Orcinol Test


  Yellow brown solution (negative) for fructose, glucose (hexoses)

  Negative for sucrose, lactose, glycogen & starch

  
• Seliwanoff's Test


  1. Test for ketoses

  2. Principle: HCl + resorcinol dehydrates ketoses which react faster to give colored products

  3. Positive result: Bright cherry red with Ketohexose (such as fructose) and disaccharides containing a ketohexose (such as sucrose)

  4. Aldohexose give pale pink color that takes longer to develop

  5. Other sugars (e.g. aldose) may produce yellow to faint pink colors
• Theoretical Results for Seliwanoff's Test


  Positive for sucrose and fructose

  Negative for glucose, lactose, glycogen, & starch

  
• Experimental Results for Seliwanoff's Test


  Positive for sucrose and fructose

  Negative for glucose, lactose, glycogen, & starch

  
• Iodine's Test


  1. Test for starch - distinguishes starch from monosaccharides, disaccharides, and other polysaccharides

  2. Principle: Polyiodide ions form colored adsorption complex with helical chains of glucose residue of amylose (blue-black), dextrin (black), or glycogen (reddish/yellowish-brown)

  3. Positive result: blue-black colored complex

  4. Negative result: yellowish brown colored complex or no color change

  
• Starch is made up of many glucose units joined by glycosidic linkage

  
• Iodine does not react with other carbohydrates that are not coiled, and remains yellowish brown
• Monosaccharides, disaccharides, and branched polysaccharides like cellulose remain colorless

  
• Amylopectin produces an orange-yellow hue
• Lugol's iodine, which is an aqueous solution of elemental iodine and potassium iodide (iodine-potassium iodide, I2KI), is the reagent used