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Agar and Gelatin

Agar is a gel-forming material found in red algae cell walls. It is composed of polysaccharides agarose and agaropectin. Agar swells in cold water and dissolves in boiling water to form a gel at low concentrations. Gelatin is obtained by boiling animal bones and tissues. It dissolves in hot water to form a gel when cooled. Unlike agar, gelatin requires temperatures around 60°C to dissolve due to its protein structure. Gelatin is not often used in microbiology as most bacteria lack enzymes to liquefy its solid form.

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756 views1 page

Agar and Gelatin

Agar is a gel-forming material found in red algae cell walls. It is composed of polysaccharides agarose and agaropectin. Agar swells in cold water and dissolves in boiling water to form a gel at low concentrations. Gelatin is obtained by boiling animal bones and tissues. It dissolves in hot water to form a gel when cooled. Unlike agar, gelatin requires temperatures around 60°C to dissolve due to its protein structure. Gelatin is not often used in microbiology as most bacteria lack enzymes to liquefy its solid form.

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Doms Gamboa
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6.

What is the difference between agar and gelatin in terms of properties like chemical composition, temperature required for melting and temperature required to solidify? Agar is a gel-forming material found in the cell wall of some species of red algae of the genus Gelidium, probably existing in the form of its calcium salt or a mixture of calcium and magnesium salts. It is a complex mixture of polysaccharides composed of two major fractions agarose, a neutral polymer, and agaropectin, a charged, sulfated polymer. Agar is insoluble in cold water, but it swells considerably, absorbing as much as twenty times its own weight of water. It dissolves readily in boiling water and sets to a firm gel at concentrations as low as 0.50%. Powdered dry agar-agar is soluble in water and other solvents at temperatures between 95 and 100 C. Moistened agar flocculated by ethanol, 2-propanol or acetone, or salted out by high concentrations of electrolytes, is soluble in a variety of solvents at room temperature. On the other hand, gelatin is a protein substance obtained by boiling animal bones and connective tissue containing collagen in water or dilute acid. In an aqueous solution it is a hydrophilic colloid. Gelatin is a colorless, transparent, brittle, odorless and tasteless in a purified form. It dissolves in hot water and forms a gel or jelly upon cooling. A temperature of about 60C is necessary in order to release the ordered structure of gelatin in its dry state. When gelatin is added to a solution its viscosity will increase. Gelatin is insoluble in organic solvents (e.g., ether, chloroform and benzene) and when placed in cold water, it takes up 5-10 times its own weight and swells to an elastic, transparent mass. 7. Why is gelatin not often used in the preparation of culture media in a microbiology laboratory? Gelatin is basically a jelly when in solid form but it can also be in liquid form. Gelatin is most efficient in preparing culture media when it is in liquid form and it so happened that most bacteria do not contain enzymes that can liquefy the gelatin. Hence, it is not often used for isolating microbes for bacterial identification. It follows that gelatin is able to support a preparation but because of its property or character, it is not frequently used in the laboratory. http://docs.google.com/viewer?a=v&q=cache:bMJCJP7etOkJ:www.weishardt.com/doc/enproprietesgelatine.pdf+gelatin+properties&hl=tl&gl=ph&pid=bl&srcid=ADGEESgapmal11PCs8scaVyASZdt2_2o2ZWafMGtETT_BqPCy6YVLW8jXMvaYJ7J3agpe_Y2kUrTFpAU23v8ch86G1blYtOt0c AsoBSE_SXfP859fkZPxRsX6bPqZMF7CPePEcXVvDi&sig=AHIEtbSyAcetuz2Idwp8KUiLCN8 dIIAmDg

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