Agar
Agar is a gelatinous substance derived from seaweed and is commonly used as a culture medium in microbiology to grow bacteria and other microorganisms. It provides a solid surface for microbial growth and is also used in food production as a thickening agent. Agar is heat stable, allowing it to be sterilized and poured into petri dishes for laboratory use.
6 Key excerpts on "Agar"
eBook - ePub- Alan Imeson, Alan Imeson(Authors)
- 2011(Publication Date)
- Wiley-Blackwell(Publisher)
...The most significant application is solid culture media for microbiology. The unique combination of properties of some Agars has made it the principal gel former in this area. Bacteriological Agars are mainly produced from Gelidium and, in lower quantities, from Pterocladia. Agars obtained from other Agarophytes and alternative gelling agents have failed to match this combination of properties (Armisen, 1991, 1995): The gel point at 36 ± 1.5°C does not damage nutrients, vitamins, antibiotics, cells and other components added to the liquid Agar prior to gelation. The large gel hysteresis, with a melting point at 87 ± 1.5°C, enables gels to be incubated up to 50°C for the study of thermophilic organisms. The polymer chains associate through hydrogen bonds at neutral pH so that gels can be formed without cations that could affect microbial growth. Agar is not metabolised or degraded by the hydrolytic enzymes in bacteria, yeast and fungi. The polymer does not react with the components used in media formulation and contains no charged groups that may affect nutrient migration or contain any substances that may inhibit or moderate cell growth. It is stable to heat treatment and withstands the long periods of autoclaving needed to sterilise the growth media prior to inoculation. It is easy to inoculate and mix liquids prior to gelation or to apply cultures to gelled plates. The gel has good clarity so it is easy to identify and count colonies. This combination of properties underpins the use of Agar as the key gelling agent for solid media in microbiology and similar application areas. In plant breeding, Agar is used to produce solid substrates for cloning plants and to propagate high-value plants, such as orchids...
eBook - ePub- Glyn O. Phillips, Peter A. Williams, Glyn O. Phillips, Peter A. Williams(Authors)
- 2009(Publication Date)
- Woodhead Publishing(Publisher)
...4 Agar R. Armisén; F. Gaiatas HispanAgar S. A., Spain Abstract Agar has its origins in Japan in 1658. It was introduced first in the Far East and later in the rest of Agarophyte seaweed producing countries. Its use was introduced in Europe in 1859 and it was being used in bacteriological culture media in 1882. This chapter discusses the seaweeds used the world over as raw material for Agar production (Agarophyte seaweeds), and presents the industrial processes used for Agar production. The chemical structure of Agar and its fractions, such as Agaroses and Agaropectines, are presented, and the relation between its chemical structures and properties are also shown. The gelation and melting of Agar and its fractions, such as Agaroses and Agaropectines, is based only in the formation of hydrogen bridges (physical gels), and thus gelation is extraordinarily reversible. The synergies and antagonisms among Agar and other products in the gelation processes are studied. Various applications of Agar are presented, in some of which Agar is irreplaceable. Use formulations are shown in food preparations. Diverse applications are also presented, in the preparation of food for insects, for plant tissue culture, and in the preparation of culture media for microorganisms, as well as gels for denture moulding, the reproduction of archaeological remains or of fingerprinting in police work. Agar gels are important in food preparations with high content in soluble gross fibre, as Agar is the food additive with the highest content in said fibre, superior to that of 94%. Lately the production of more easily soluble Agars in water at temperatures below boiling point has been initiated, which proves to have noteworthy advantages for some of its applications...
eBook - ePubPolysaccharides
Properties and Applications
- Mohd Imran Ahamed, Rajender Boddula, Tariq Altalhi, Mohd Imran Ahamed, Rajender Boddula, Tariq A. Altalhi(Authors)
- 2021(Publication Date)
- Wiley-Scrivener(Publisher)
...5 Agars: Properties and Applications Sudhakar Padmesh and Aditi Singh * Amity Institute of Biotechnology, Amity University Uttar Pradesh, Lucknow Campus, Lucknow, India Abstract The roots of origination of Agar belong to Japan. Agar was firstly known to come into the use in 1658. It was extracted from Gracilaria, an Agarophyte seaweed which was used in food stuff back then. Agar was firstly introduced in far-east countries and later it was taken to the rest of the Agarophyte producing countries. After so many uses of Agar were introduced in Japan, it started to attract European countries and was introduced there in 1859 and then its use in microbiology study started in 1882. This comprehensive review describes the history of Agar and uses of its seaweed worldwide, the production and origination of Agar, industrial, biological uses as well as uses of Agar in food industry. A substance made up of replicated molecules of repeated Agarobiose units, is called Agar. However Agarose is a least substituted Agar molecule with the highest gelling potential. The family of Agar algae and its polysaccharide is dynamic. Physico-chemical and chemical properties defines the Agar population through-out the algal families, and changes with the change in physicological, cellular and environmental grounds. Thus modifications in biochemistry of this molecule should be explicated. The chemical and molecular structure of Agar, its fractions like Agarose and Agaropectin, the hydrogen bridges formed in its gelling formation, as well as a comparative study of types of Agar derived from different seaweeds along with the different types of commercially produced Agar food products will be discussed in this chapter. Keywords : Gracillaria, Agar, Agaropectin, Agarophyte, seaweed, hydrogen bridges 5.1 History and Origin of Agar The first known use of Agar was in Japan in 1658, when it was used as a food gelling material...
eBook - ePubNatural Polymers for Pharmaceutical Applications
Volume 2: Marine- and Microbiologically Derived Polymers
- Amit Kumar Nayak, Md Saquib Hasnain, Dilipkumar Pal, Amit Kumar Nayak, Md Saquib Hasnain, Dilipkumar Pal(Authors)
- 2019(Publication Date)
- Apple Academic Press(Publisher)
...In addition, Agar-Agar takes up bile and hence help the body to process more cholesterol. 3.5.2 SURGICAL AND MEDICAMENT PREPARATION Agar-Agar has diversified applications in the pharmaceutical industries. Agar-Agar is used for preparing capsules, incipient in tablets, aiding surgical action by providing lubrication and acting as the suspending agent in radiology (Figure 3.5). Sulfated Agar has the ability to lower lipid levels in blood like heparin. The most common use of Agar-Agar in the laboratory is probably in the culture medium for the bacterium. 3.5.3 OTHER APPLICATIONS Apart from pharmaceutical use, Agar-Agar has diverse applications in many fields such as an ingredient in the culture medium, pesticide detector, and especially in food preparation. Use of silver nanoparticles in Agar matrix has found its application as an antimicrobial thin film. In the process, very stable silver nanoparticles are mixed with Agar matrix to prepare a thin organic-inorganic hybrid film. This film can be reused; however, due to the loss of silver nanoparticles, the efficiency drops. The Antimicrobial test results show that it is most effective for C. albicans and retained its microbial property even after three cycles of reuse. Antimicrobial films may be promising for food packaging, wound dressing, and as sterile coatings (Ghosh et al., 2010). FIGURE 3.5 (See color insert.) Pharmaceutical applications of Agar-Agar. In agrochemical delivery, Agar-based super sorbent, pH sensitive, the hydrogel has been prepared by Pourjavadi et al., The maximum water absorbency in distilled water was more than 1000 g/g. Potassium nitrate was loaded to check the efficiency of the hydrogel for the sustained release of potassium. Copolymerization of acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid on Agar produced a hydrogel, which released potassium sharply in the initial state and leveled off afterward (Pourjavadi et al., 2009). Food packaging films can also be made from Agars...
eBook - ePub- Clàudia Cortés, Núria Cubero, Laura Gómez, Albert Monferrer(Authors)
- 2020(Publication Date)
- CRC Press(Publisher)
...4 E-406 Agar E - 406 Agar (CAS Number: 9002-18-0) Other denominations: Agar-Agar, kanten Origin It is obtained from red algae’s cell walls, also called Agarophyte algae, in particular of some species of the genus Gelidium, Pterocladia, Ge/idle/la, Gracili- aria and Gracilariopsis (Figure 1). Composition and chemical structure It is a heteropolysaccharide formed by two polysaccharides: Agarose (Figure 2) and Agaropectin (Figure 3). The proportion between the two types of molecules depends on the type of algae and the extraction process, but is generally 70% Agarose and 30% Agaropectin. (Figure 4) Table 1 describes the main differences between the two molecules. Properties of solutions Solubility and solutions preparation Agar is insoluble in cold water. It starts to solubilize in hot water, becoming completely soluble in boiling water. As with most hydrocolloids, it is recommended to premix Agar with other powdered products before adding it to the aqueous medium and apply shear force to disperse it correctly, although it does not tend to form It does not incorporate air in the mix process, so it is not necessary to leave a rest time for defoaming. It also does not provide a significant increase in the viscosity of the medium and is stable in the presence of high concentrations of alcohol (Table 2). Table 1. Differences between molecules of Agarose and Agaropectin Molecule Ionic charge Gelling capacity Sulfate content Agarose Neutral Yes Very low Agaropectin Negative charge No High Figure 1. Diagram of the obtaining process of Agar Factors affecting the properties of solutions ● Temperature: it must reach a high enough temperature to completely solubilize Agar, it is recommended to exceed 90°C (Table 3). ● pH: in acidic mediuma, a hydrolysis of the Agar molecule is produced. If the medium is not neutralized with a base before the solubilization of the Agar, it may cause the loss of the gelling ability...
eBook - ePub- James N. BeMiller(Author)
- 2018(Publication Date)
...A κ-, λ-carrageenan blend is used in milk shakes. Labels of products containing κ-, λ-, or ι-type carrageenans may read carrageenan, chondrus extract, or Irish moss extract. The label designation of PES/SRC/PNG carrageenan may be carrageenan. Agar: structure and uses Agar is a thermoreversible gelling agent composed of two polysaccharides. Agarose (or Agaran) is a linear chain of 3- O -substituted β- D -galactopyranosyl units joined by (1 → 4) linkages to 3,6-anhydro-α- L -galactopyranosyl units. (Note that the anhydrosugar in Agar has the L configuration.) Agarose is the gel-forming component. Agaropectin is a branched, nongelling component of Agar. Small amounts of sulfate half-ester groups and pyruvate 3,6-cyclic acetal groups (Chapter 2) may be present. Considerable amounts of methyl ether groups are also present. These structural characteristics make Agar the least hydrophilic and least water soluble of the red seaweed polysaccharides. Usually, Agar can only be dissolved in water at 100°C (boiling) or higher temperatures, although preparations that hydrate and dissolve at about 80°C are available (with and without standardizing materials). The principal use of Agar is in bakery icings and frostings because it is compatible with large amounts of sugar and its products neither melt at high storage temperatures (such as might be found in a delivery truck) nor stick to the packaging material. It is also used in light sour cream, no-oil salad dressings, and yogurt. Its use is limited by its high price...
