Page 45 - PG 504-theoretical notes-phyto-1-2024-2025..

Clinical pharmacy PharmD program Third level Phytochemistry-1 (PG-504)

Non-reducing carbohydrates include:

• Some disaccharides, e.g., sucrose, trehalose.

• Polysaccharides.

The non-reducing carbohydrate will be converted into reducing sugars on

hydrolysis upon boiling with acids and give positive test, but the acid has to be

neutralized before adding Fehling’s solution, otherwise Cu 2O will fail to be

precipitated.

3) Osazone formation: (see latter).

Osazone are sugar derivatives formed by heating a sugar solution

with phenylhydrazine, sodium acetate and acetic acid. They are yellow

crystalline products sufficiently characteristic for identification of certain sugars

by their microscopic examination and melting point.

• Glucose, mannose and fructose form the same and identical osazone (why?).

• Sucrose does not form osazone but under the test condition, sufficient

hydrolysis takes place enough for the production of some glucosazone.

4) Resorcinol test for ketoses “Seliwanoff’s test”: (See latter)

To carbohydrate solution, add a crystal of resorcinol and an equal

volume of conc. HCl, warm on water bath. Development of red color indicates

a ketose is, e.g., fructose.

5) Test for pentose: (See latter)

a) Phloroglucinol test:

A solution of carbohydrate is heated with an equal volume of conc. HCl

containing a little phloroglucinol. A red color indicates pentose.

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