Neomycin agar
5.9.4 Culture Media for Microbes
Different types of agar medium which are broadly being used in various science fields are shown in Table 5.4. In 1882, Robert Koch started the utilization of agar gel as a medium in microbial cultivation. Ever since then no other substance has taken place of it, especially in microbiology.
5.9.5 Industrial Applications of Agar
From sculpture molds to forensic preserve, agar is being utilized in various industries. In 1980, Meer developed the dental molds using the agar, since then agar has been of significant use in dentistry. In archaeology, agar is used to as a molding agent for sculptures. In forensic science, agar is used as a molding agent to preserve finger prints and other crime related clues. Usually sorbitol or glycerine is used to avoid any synergies in these gels. These humidifier agents absorb the environmental moisture to reimburse for any evaporation losses.
5.10 Conclusion and Discussion
The last decade has been remarkable for agar. A number of researches were made to obtain agar of greater gel strength and of lower dissolving power at higher temperature (mainly above boiling temperature of water i.e. 100 °C). Commonly, 20 min time is sufficient to completely dissolve agar in water, while maintaining the gel strength. Strength of commercially produced agar gel is mainly depends upon its repeating units of agarose in relation to their agaropectin contents. Agarose content in agar also determines its solubility in different solvents. It has been observed that agarose with molecular of 240 kD or higher, takes more time than the agaroses with lower molecular weight. Nonetheless agarose with even higher molecular weight require extra pressure and higher temperature around 121 °C or higher. A faster solution for this is xerogels. Xerogels are most hydrophilic structures and obtained by milling the dehydrated gel with synergies. This results in a fine grounded powder that bloats a lot due to more contact with the warm water and larger number of agarobiose molecules.
When agar is dissolved in water, its viscosity is decreased and which helps agar in dissolving nicely into water. It should be taken into account, when adequate amount of calcium ions are present between various agaropectins and helps them building structure of higher molecular weight, it helps in reducing the viscosity of agar in water. These ionic bonds have tendency to distort the molecular weight statistical measurements of agar. These ionic bonds emerge only when calcium or any other alkali metals are there in the agar. Agar solutions can be prepared faster with addition of influencing substances before extraction and drying of agar. However, agar prepared using these determining substances may cause problem when a batch experiment of agar will be needed.
References
1. Mantell, C.L., ‘Agar’, in division R.L. (ed.), The Water-Soluble Gums, pp. 75–119, Haefner Publishing Company, New York, 1965.
2. Glicksman, M., Agar. in: Seaweed extracts: Gum technology in the food industry, pp. 199–266, Academic Press, New York, 1969.
3. Glicksman, M. (ed.), Agar. Food Hydrocolloids, volume II, pp. 74–83, CRC Press, Boca Raton, FL, 1983.
4. Stanley, N.F., Agars, in Food Polysaccharides and Their Applications, Stephen, A.M. (Ed.), pp. 187–204, Marcel Dekker, New York, 1995.
5. FDA, Agar-agar, GRAS (generally recognised as safe) Food Ingredients, Food and Drug Administration, PB-221225 NTIS, US Department of Commerce, Bethesda, MD, 1972.
6. FDA, Evaluation of Health Aspects of Agar-agar as a Food Ingredient, Food and Drug Administration, PB-265502, Federation of American Societies for Experimental Biology, Bethesda, MD, 1973.
7. FDA, Teratologic Evaluation of FDA 71-53, PB-223820, US Department of Commerce, Washington, DC, 1973.
8. FDA, Mutagenic Evaluation of FDA (agar-agar) 71-53, PB-245443, US Department of Commerce, Washington, DC, 1973.
9. Armisén, N.R., Worldwide use and importance of Gracilaria. J. Appl. Phycol., 7, 231–243, 1995.
10. Yanagawa, T., Kanten (Agar), 2nd Edn, p. 352, Sangiotosho Co. Ltd, Tokyo, Japan, 1946.
11. Okazaki, A., Seaweeds and their Uses in Japan, Tokai University Press, Tokyo, 1971.
12. Lahaye, M. and Rochans, C., Chemical structure and physico-chemical properties of agar. Hydrobiologia, 221, 137–148, 1991.
13. Rees, D.A., Enzymic synthesis of 3:6-anhydro-l-galactose within porphyran from l-galactose 6-sulphate units. Biochem. J., 81, 2, 347–352, 1961.
14. Usov, A.I., Ivanova, E.G., Makienko, V.F., Polysaccharides of algae. XXIX: Comparison of samples of agar from different generations of Gracilaria verrucose (Huds.). Papenf. Bioorg. Khim., 5, 1647–1653, 1989.
15. Yanagawa, T., Kanten (Agar), 2nd Edn, p. 352, Sangiotosho Co. Ltd Tokyo, Japan, 1946.
16. Guiseley, K.B., The relationship between methoxy content and gelling temperature of agarose. Carbohydr. Res., 13, 247–256, 1970.
17. Izumi, K., A new method for fractionation of agar. Agric. Biol. Chem., 34, 1739–1740, 1970.
18. Rees, D.A. and Welsh, E.J., Secondary and tertiary structure of polysaccharides in solution and gels. Angew. Chem. Int. Ed. Eng., 16, 214–224, 1977.
19. Guiseley, K.B., The relationship between methoxy content and gelling temperature of agarose. Carbohydr. Res., 13, 247–256, 1970.
20. Lahaye, M. and Rochans, C., Chemical structure and physic-chemical properties of agar. Hydrobiologia, 221, 137–148, 1991.
21. Hirase, S., Studies on the chemical constitution of agar-agar, XIX. Pyruvic acid as a constituent of agar-agar (Part-3). Structure of the pyruvic acid-linking disaccharide derivative isolated from methanolysis products of agar. Bull. Chem. Soc. Jpn., 30, 75–79, 1957.
22. Furneaux, R.H., Miller, I.J., Stevenson, T.T., Agaroids from New Zealand members of the Gracilariaceae. A novel dimethylated agar. Hydrobiologia, 204/205, 454–654, 1990.
23. Rees, D.A., Enzymatic synthesis of the 3,6-anhydro-L-galactose with porphyran from L-galactose 6-sulphate units. Biochem. J., 81, 347–352, 1961.
24. Arnott, S., Fulmer, A., Scott, W.E., Dea, I.C.M., Moorhouse, R., Rees, D.A., Agarose double helix and its function in agarose gel structure. J. Mol. Biol., 90, 269–284, 1974.
25. Watase, M. and Nishinari, K., Effect of alkali metal ions on the rheological properties of κ-carrageenan and agarose gels. J. Texture Stud., 12, 427–445, 1981a.
26. Watase, M. and Nishinari, K., Effect of sodium hydroxide pretreatment on the relaxation spectrum of concentrated agar-agar gels. Rheol. Acta, 20, 155–162, 1981b.
27. Watase, M. and Nishinari, K., Effect of alkali metal ions on the viscoelasticity of concentrated kappa-carrageenan and agarose gels. Rheol. Acta, 21, 318–324, 1982.
28. Chiles, T.C., Bird, K.T., Koehn, F.E., Influence of nitrogen availability on agar-polysaccharides from Gracilaria verrucosa strain G-16: Structural analysis by NMR spectroscopy. J. Appl. Phycol., 1, 53–58, 1989.
29. Whyte, J.N.C. and Englar, J.R., The agar component of the red seaweed Gelidium purpurascens. Phytochem., 20, 237–240, 1981.
30. Izumi,