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Mucic Acid Test For Galactose and Lactose

Mucic acid test for galactose and lactose post we briefly summarises about: principle, reagents requirements, procedure, result, application and limitations of mucic acid test.

Mucic Acid Test For Galactose and Lactose

Why is the mucic acid test specific for the presence of galactose?, Mucic acid test is for galactose and lactose. A sugar is oxidised to carboxylic acid by hot nitric acid. To produce dicarboxylic acids, aldoses are oxidised at both ends of the ring-opened form.

Chain fragmentation causes ketoses to oxidise, resulting in a variety of dicarboxylic acids. Galactaric acid (mucic acid) produced by the oxidation of galactose has a lower solubility in the oxidising media (including water) than saccharic acids produced by other aldoses. This owes in part to galactraric acid’s strong molecular symmetry.

Purpose

  • To detect the presence of galactose and lactose in a given sample.
  • To distinguish between the galactose containing saccharides and other sugars.

Principle

Monosaccharides like galactose, (galactose containing sugars such as lactose gives positive response to this reaction). The presence of strong acids like nitric acid, produce saccharic acids. The saccharic acid formed is insoluble and form clear crystals. This acid derivative is known as galactaric or meso-galactaric acid (mucic acid), thus the name for the test.

Mucic Acid Test For Galactose and Lactose

Mucic Acid Test Equation

Requirements

Reagent

  1. Mucic acid test reagent: concentrated nitric acid
  2. Test sample (1%)
  3. Distilled water

Materials

  1. Test tubes
  2. Test tube stand
  3. Pipette

Equipment

  1. Water bath

Procedure

  1. Mix 3 drops of the carbohydrate solution (galactose and lactose) and 3 drops of the concentrated Nitric Acid on a glass slide
  2. Pass the mixture over a small flame until it is almost dry. Cool the mixture at room temperature; examine the crystals under the microscope.

Test Results

Mucic Acid Test For Galactose and Lactose

Mucic acid test positive result colour,  Insoluble precipitate or crystals which indicate the presence of a galactose. The results viewed under the microscope with high power objective were rectangular in shape and only a few in numbers. The result of the experiment yield to insoluble precipitate which is a positive result for test.

Uses

  1. Mucic acid test is most commonly used to detect galactose or its derivatives in food samples and in the production of synthetics. Mucic acid test can also be used to determine whether lactose or agar-agar is present.

Limitations

  1. Mucic acid test is unable to distinguish between monosaccharide and disaccharide galactose derivations. Impurities with carbonyl groups at the terminal ends can cause a false positive result in some situations.

Further Readings

Reference