Biochem: Carbohydrates (Lab)

• a common test for all carbohydrates larger than tetroses

  Molisch test
• In Molisch test, pentoses and hexoses are dehydrated by ___ to form furfural or hydroxymethylfurfural

  conc. sulphuric acid
• Product color in Molisch test:

  purple ring at the junction of two solutions
• reduction test of carbohydrates

  Fehling’s Test
• Product color in Fehling's test:

  yellow or brownish red colored precipitate
• As in Fehling’s test, free aldehyde or keto group in the reducing sugars

  Benedict’s Test
• Product color in Benedict's test:

  yellow to green color
• True or False: All monosaccharides are reducing sugars as they all have a free reactive carbonyl group.

  True
• Reducing sugars (glucose & lactose) reduce silver ions in the test reagent to elemental silver.

  Tollen’s Test
• Product color in Tollen’s Test:

  a silver mirror on the inner surface
• Test to detect the presence of monosaccharide (reducing) sugars in solution

  Barfoed’s Test
• Product color in Barfoed’s Test:

  red copper(II) oxide precipitate
• When conc. HCl is added, ketoses undergo dehydration to yield furfural derivatives more rapidly than aldoses.


  Seliwanoff’s Test
• Product color in Seliwanoff’s Test:

  cherry red color (fructose and sucrose)
• This test is used for the detection of starch in the solution.

  Iodine’s Test
• Product color in Iodine’s Test:

  blue black color
• HCl when reacted with pentose sugar (such as ribose sugar) forms furfural derivative

  Bial’s (Orcinol) Test
• Product color in Bial’s Test:

  blue color (pentose)
• Monosaccharide reacts with phenylhydrazine resulting in the formation of osazones


  Osazone Test (Phenylhydrazine Test)