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: To 2 mL of the aqueous solution, add 2 drops of alpha-naphthol in ethanol. Add 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 sample and heat. A brick-red precipitate of cuprous oxide indicates the presence of reducing sugars.
3. Benedict's Test: Add the sample to Benedict's reagent and boil. A green, yellow, or red precipitate indicates the presence of reducing sugars.
4. Barfoed's Test: Used to distinguish monosaccharides from disaccharides. Monosaccharides produce a red precipitate within 1-2 minutes of boiling.
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 composed of monosaccharide units linked by glycosidic bonds. In pharmacognosy, they serve as important therapeutic agents, excipients, and diagnostic tools.

Key polysaccharide drugs include:

• Starch: Obtained from Zea mays or Oryza sativa. It consists of amylose and amylopectin. Used as a disintegrant, binder, and dusting powder in pharmaceutical formulations.
• Acacia (Gum Arabic): A dried gummy exudate from Acacia senegal. It is a complex mixture of calcium, magnesium, and potassium salts of arabic acid. Used as a suspending agent, emulsifier, and binder.
• Tragacanth: Obtained from Astragalus gummifer. It contains bassorin and tragacanthin. Used as a thickening agent and stabilizer in emulsions and gels.
• Agar: A dried gelatinous substance extracted from Gelidium amansii. It is a polymer of agarose and agaropectin. Used as a bulk laxative and as a culture medium in microbiology.
• Isabgol (Psyllium): Dried seeds of Plantago ovata. The mucilage is highly hygroscopic and is used as a bulk-forming laxative to treat chronic constipation.

These drugs are generally classified as either homopolysaccharides (composed of one type of sugar, e.g., starch, cellulose) or heteropolysaccharides (composed of different sugars or sugar derivatives, e.g., gums, mucilages, pectin).