JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD Pharm. D II Year PHARMACOGNOSY AND PHYTOPHARMACEUTICALS Previous Question Paper (October/November - 2019 - R08)

Carbohydrates are identified using the following chemical tests:

1. Molisch's Test: Add 2 drops of alpha-naphthol solution to the test solution, followed by the addition of concentrated sulfuric acid along the sides of the test tube. A violet ring at the junction indicates the presence of carbohydrates.
2. Fehling's Test: Mix equal volumes of Fehling's A and B solutions and boil. Add the test solution and heat. A brick-red precipitate of cuprous oxide indicates the presence of reducing sugars.
3. Benedict's Test: Add the test solution to Benedict's reagent and boil. A green, yellow, or red precipitate indicates reducing sugars.
4. Barfoed's Test: Used to differentiate monosaccharides from disaccharides. Monosaccharides produce a red precipitate with Barfoed's reagent upon heating.
5. Iodine Test: Used for starch. Addition of dilute iodine solution produces a blue-black color, which disappears on heating and reappears on cooling.
6. Osazone Test: Reducing sugars react with phenylhydrazine to form characteristic crystalline osazones, which can be identified by their shape under a microscope.

Polysaccharides are high molecular weight polymers of monosaccharides linked by glycosidic bonds. They are classified into homopolysaccharides (composed of one type of sugar) and heteropolysaccharides (composed of different types of sugars). In pharmacognosy, they serve as important therapeutic agents, excipients, and dietary fibers.

Key polysaccharide drugs include:

• Starch: Obtained from maize, rice, or potato. It acts as a disintegrant, binder, and diluent in tablet formulations.
• Acacia (Gum Arabic): A dried gummy exudate from Acacia senegal. It is used as a suspending agent, emulsifier, and binder in pharmaceutical preparations.
• Tragacanth: A dried gummy exudate from Astragalus gummifer. It is used as a thickening and suspending agent due to its high viscosity.
• Agar: A dried gelatinous substance obtained from marine algae (Gelidium amansii). It is used as a laxative and a solidifying agent in culture media.
• Isabgol (Psyllium husk): Obtained from the seeds of Plantago ovata. It is a rich source of mucilage and is widely used as a bulk laxative to treat chronic constipation.
• Pectin: A purified carbohydrate product obtained from the inner portion of the rind of citrus fruits. It is used as a gelling agent and in the treatment of diarrhea.