Medicinal Plants Lecture 8

Medicinal Plants Lecture 8

• Lecture is about reserved food materials in plants, specifically carbohydrates, proteins, fixed oils, fats, and waxes.
• Reserved food materials are also known as primary metabolites.
• Reserved food material in plants include carbohydrates, proteins, fixed oil, fat and waxes.

Inulin

• Inulin replaces starch as the reserved carbohydrate in subterranean organs of plants in the Compositae family.
• It is composed of β-D-1,2-furanofructose.
• It can be hydrolyzed by acids into D-fructose but not by the enzyme amylase.
• Inulin is a white powder slightly soluble in cold water and does not react with iodine.
• Inulin is used in culture media as a fermentative identifying agent for certain bacteria.

Cellulose

• Cellulose is the main component of plant cell walls.
• It's a linear β-1,4 polymer of glucose containing 300-25,000 glucose residues.
• Human digestive enzymes cannot hydrolyze the β linkages of cellulose.
• Concentrated mineral acids (HCl, H2SO4, or HNO3) can hydrolyze cellulose to β-D-glucose units.
• Cellulose is used as a surgical dressing.

Mucilage

• Mucilage is a complex polysaccharide found in the cell walls of roots, rhizomes, leaves, and seed endosperm.
• It forms a viscous, colloidal solution without adhesive properties.
• There are three types of mucilage: neutral, acidic, and seaweed mucilage.
• Neutral mucilage consists mainly of D-mannose and D-galactose.
• Acidic mucilage contains uronic acid residues (mainly galacturonic acid) and other sugars like D-galactose, xylose, arabinose, and rhamnose.
• Seaweed mucilage is composed of polysaccharide sulphate esters.
• Mucilage is used as a demulcent, cathartic, antidiabetic, and for preventing colon cancer.

Pectin

• Pectin is produced during the ripening of citrus fruits.
• It dissolves in water to form a viscous colloidal solution, but without adhesive properties.
• Pectin acts as a protective agent, binding and absorbing toxins, and is used in treating intestinal disorders like diarrhea and dysentery.
• It is used in pharmacy as a stabilizer in gels and emulsions.
• It's also used to prepare jellies and as a slimming agent (e.g., Applelite tablets).

Gum

• Natural gums are polysaccharides of natural origin, increasing solution viscosity at low concentrations.
• Used in food industry as thickening, gelling, emulsifying agents, and stabilizers.
• Also used as adhesives and binding agents in other industries
• Gums form viscous colloidal solutions with adhesive properties.
• Commonly found in woody plant tissues and seed coatings.
• They are essentially protective substances produced by plants after injury or pathologically. Examples include gum acacia and gum tragacanth.

Chitin

• Chitin is a nitrogenous polysaccharide found in certain shrimps and fungi.
• It is insoluble in water and alcohol but soluble in strong mineral acids.
• Hydrolysis with strong acids yields glucosamine.
• Chitin stains a brown color with iodine-potassium iodide solution.
• It's composed of N-acetyl-D-glucosamine units linked by 1,4-β-glycosidic bonds.

Protein Content of Plants

• Plant proteins are nitrogenous organic reserves with high nutritive value.
• Proteins consist of polypeptides, dipeptides, and amino acids when hydrolyzed.
• Stored as clumps or small particles called aleurone grains throughout the living cells.
• Aleurone grains are common in oily cells rather than starchy cells.
• The simplest aleurone grains consists of a protein mass surrounded by thin membrane which includes globoid and crystalloid bodies..
• Characteristically, proteins are insoluble in organic solvents and can be precipitated or coagulated via heat, pH change, or high salt concentration.
• Proteins (microscopically) can be identified via various chemical tests; e.g. a red precipitate with Millon's reagent. Picric acid solution stains crystalloid yellow but leaves globoid unstained.

Fixed Oils, Fats, and Waxes

• Fixed oils, fats, and waxes are reserved food materials in plants and animals.
• They are esters of fatty acids with glycerol.
• They can appear as liquids (oils), semisolid (fats), or solid (wax).
• Insoluble in water or cold alcohol, but soluble in ether, chloroform, petroleum ether, and benzene.
• Hydrolyzed by aqueous alkalis, resulting in fatty acid salts (soap).
• Fixed oils are categorized by their ability to absorb and form hard films (e.g., drying oils, semi-drying oils, and non-drying oils).