Carbohydrate

Carbohydrates

• Definition:

  • Carbohydrates are polyhydroxy aldehydes or ketones, or compounds that can be hydrolyzed to them.

  • Typically contain carbon, hydrogen, and oxygen in a ratio similar to water: CX(H2O)Y.

  • Examples:

    • Glucose: C6H12O6 = C6(H2O)6

    • Fructose: C6H12O6 = C6(H2O)6

    • Ribose: C5H10O5 = C5(H2O)5

Chemical Behavior

• Some compounds behave chemically like carbohydrates but do not fit the CX(H2O)Y formula:

  • Rhamnose: C6H12O5

  • Compounds like formaldehyde (HCHO/CH2O) and acetic acid (CH3COOH/C2(H2O)2) have the same formula but are not considered carbohydrates.

Classification of Carbohydrates

• Carbohydrates can be classified into three main categories:

  1. Monosaccharides:

     • Cannot be hydrolyzed into simpler carbohydrates.

     • Types:

       • Aldoses: e.g., Glucose, Xylose

       • Ketoses: e.g., Fructose, Ribose

  2. Oligosaccharides:

     • Yield 2 to 9 monosaccharides units upon hydrolysis.

     • Types:

       • Disaccharides: Yield two monosaccharides (e.g., Sucrose, Lactose).

       • Trisaccharides: Yield three monosaccharides (e.g., Raffinose).

       • Tetrasaccharides: Yield four monosaccharides (e.g., Stachyose).

  3. Polysaccharides:

     • Yield many monosaccharide units upon hydrolysis (e.g., Starch, Cellulose, Glycogen).

Properties of Carbohydrates

• Monosaccharides:

  • White crystalline solids that melt sharply.

  • Readily soluble in water; less soluble in alcohols, insoluble in ether.

• Disaccharides:

  • Exhibit properties similar to monosaccharides.

• Polysaccharides:

  • Amorphous, do not melt sharply, less soluble in water, and insoluble in alcohol.

Importance of Carbohydrates

• Biological:

  • Most abundant constituents of plants and animals.

  • Major source of caloric intake for humans and animals; essential for microorganisms.

• Pharmaceutical:

  • Antibiotics like streptomycin and neomycin are carbohydrates with antimicrobial properties.

  • Commonly used as excipients like diluents and sweetening agents in pharmaceuticals.

Specific Carbohydrates

• Dextrose (α-D(+)-glucopyranose/D-glucose):

  • Found in grapes; obtained by starch hydrolysis.

  • Properties:

    • Dextrorotatory, optical rotation of 52.5° to 53°.

    • Reducing agent in Tollens and Fehling’s reagents.

  • Uses:

    • Ingredients in dextrose injections and solutions.

• Fructose (β-D(-)-fructopyranose/D-fructose):

  • Naturally occurs in sweet fruits and honey; obtained through sucrose hydrolysis or inulin.

  • Cyclic forms include furanose and pyranose structures.

  • Properties:

    • Colorless crystals, sweet taste, freely soluble in water.

  • Uses:

    • Sweetening agent for diabetic foods and in pharmaceuticals.

• Sucrose:

  • Derived from sugar cane and sugar beet; produced in many countries.

  • Properties:

    • Disaccharide with formula C12H22O11; non-reducing sugar.

  • Production:

    • Juice extracted from crushed stems; purified and crystallized from cane/beet juice.

  • Uses:

    • Syrup preparation, preservatives, taste masking for medications.

Other Carbohydrates and Compounds

• Liquid Glucose:

  • Obtained from starch hydrolysis, sweet-tasting syrup containing dextrose.

  • Uses:

    • Pharmaceutical necessity, tablet binder, cocoa syrup ingredient.

• Dextrin:

  • An incomplete hydrolysis product of starch; used as an excipient and adhesive.

• Gums and Mucilages:

  • Polysaccharides from plants; dissolve in water and used for suspending and emulsifying agents.

Plant Extracts

• Tragacanth:

  • Exudate from Astragalus species; used as a suspending and emulsifying agent.

• Acacia:

  • Exudate from Acacia senegal; used as a binder in tablets.

• Sterculia:

  • Gummy exudate used as a suspending agent and laxative.

• Agar:

  • Extracted from red algae; used in culture media as a gel and suspending agent.

• Na-alginate:

  • Extracted from brown seaweeds; primarily used as a suspending agent.

Starch

• Present in green plants; major sources include maize, wheat, and potatoes.

• Composed of:

  • α-amylose: Linear glucose units.

  • Amylopectin: Branched glucose units with α-1, 4 and α-1, 6 linkages.

• Uses:

  • In pharmaceuticals as diluents, binders, and disintegrators; paper and cloth sizing, absorbent properties.

Cellulose

• Chief component of plant fibers; used in tablets as diluents or adsorbents.

• Composed of long chains of glucose units linked by β-1, 4-glucosidic bonds.