Experiment-2
Aim-Qualitative Tests for Carbohydrates
Potato consists of different carbohydrates like starch, reducing sugars etc. Difficulties are
encountered in the qualitative and quantitative analysis of samples containing mixtures of
carbohydrates, particularly the sugars, because of their structural and chemical similarity and also
with respect to their stereoisomers. During biochemical investigations it may because necessary to
establish whether a given sample, particularly of a purified preparation, consist carbohydrates or
not. Several rapid tests are available the presence or absence of a sugar or a carbohydrate in a
sample. These tests are based on specific colour reactions typical for their group and are described
below. For laboratory practical, it may be advised to perform these tests with the individual rather
than mixture of sugars. Use of sugar solutions of different concentrations (0.1-1%) during these
experiments would also provide valuable information about the sensitivity of these tests. The
types of carbohydrates detected by these tests are:
Name of the test Application
1. Molisch’s Test General test for carbohydrates
2. Anthone Test General test for carbohydrates
3. Iodine Test For glycans (starch, glycogen)
4. Barfoed’s Test To distinguish between mono-saccharides from reducing diasaccharides
5. Seliwanoff’s Test For Ketones
6. Fehling’s Test For reducing sugars
7. Bendict’s Test For reducing sugars
8.
9. Picric acid Test For reducing sugars
10. Bial’s Test For pentoses
Identification of the nature of Carbohydrates in a given sample
Principle
Some of the qualitative tests for carbohydrates are quite specific. Hence, by a judicious
section of the appropriate tests, a systematic experimental sequence can be employed to
establish whether a given test solution preparation contains carbohydrates and, if so, its
nature as well.
Procedure
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