Agar agar is a kind of complicated water-soluble polysaccharide compound, a lyophilic colloid refined from red algae gelidium and gracilaria. The common types of agar agar are: blood agar, chocolate agar, LB (Luria Bertani) Agar, MacConkey Agar, Miller's LB Agar, Neomycin Agar, non-nutrient agar, nutrient agar, Sabouraud agar, Thayer-Martin Agar, Tryptic Soy Agar and XLD Agar.

Properties
Agar agar is a white or light yellow product being powdered or strip-shaped. It doesn't smell bad or has a slight special smell. It doesn't dissolve in cold water or organic solvent but it is easy to dissolve in boiling water. After it dissolves in hot water, it can form solid gel even if the thickness is very low. If the thickness is below 0.1%, agar agar doesn't solidify and become thick liquid. If the thickness is 1.5%, agar agar will solidify at 32 to 42 degrees; the gel is of elasticity and can remelt only after being heated to 85 degrees.
The special applications of agar agar are related to its properties. For agar agar solution of the same thickness, the gelling point of collosol is different from the melting temperature of gel. Besides, agar agar has swelling capacity in water. For agar agar of 5-10%, the collosol is of high viscosity. The characteristics of agar agar depend on its manufacturing method and raw material.

Applications
Agar agar has a wide range of applications. It can be used in baking industry, confectionery industry, dairy industry, microorganism culture medium, dental surgery, pharmaceutical industry, meat industry and other industries. It has had a long history since agar agar was used in food industry. Agar agar was first used for food in the East and then it was used all round the world. It has been found that agar agar is safe to use in food industry. The Food and Drug Administration (FDA) has listed agar agar as safe food.
Agar agar has gelling, thickening and stabilizing properties, so it is mainly used as gelling agent, thickening agent and stabilizers in food industry. It is applicable to the production of many kinds of food. It is added to pie as additive and incremental agent to reduce cracks and dryness. It is added to sugar coating and icing as abherent. It is added to bread and deserts as softening agent. It is added to chocolate candy to make candy more delicious and reduce cracks. It is used in canned meat as coagulant and stabilizer to improve the mouthfeel and appearance and reduce cracks during transportation, especially when canned meat is semifluid, agar agar is quite necessary. For smoked and salted meats, it is often used to protect the meat from losing flavors. In dairy industry, it is used to reduce the dairy products from pulp and improve the thickness and slice ability of cheese.
Agar agar is an indispensable basic material in microorganism culture. It has great promoting effect in the research and development of microorganism. Most of microorganism can't disassimilate agar agar. High quality agar agar doesn't contain anything that inhibits the growth of microorganism; it has low solidifying point and high melting point, so it can form hard and elastic gel with stable transparency. The above properties enable agar agar to be an irreplaceable material in microorganism culture medium. The thickness of common used agar agar is between 1% and 2%. If the thickness is between 0.007% and 0.03%, the agar gel can prevent oxygen from easily entering into liquid medium so as to allow anaerobic culture of broth in the air. In addition, agar agar's application in tissue culture quickly develops. It plays an enormous role in vegetative propagation of vegetables and flowers, and mass production of virusfree plant.
Agar agar is also widely used in medicine and pharmacy. It is of strong water-retaining capacity and good lubrication without any irritant matter. It is good for motion of the intestine, so it can be used as laxative. In the production of medicine grain and tablets, it can be used as loose agent. In the production of ointment, it can be used as emulsifier and stabilizer in surgical dressings. In radiology, it can be added into barium sulphate as suspending agent. Agar agar is also applied to prosthodontia, technology of getting proof of guilty, manufacturing technology of instruments, tools and equipment, and manufacturing other scraggly, intricate and accurate mould. The amount of agar agar is between 6% and 14%.

Prospects
Much more new uses of agar agar are discovered continuously. For example, agar agar can be used as retarder in deep well cement setting and hardening. In citric acid solution and malic acid solution, it can be used as iron corrosion inhibitor. It is an important component of Fe-Ni-Cr-Ti electrolyte solution for electroplating steel surfaces. In atomic reactor, it can be used as instantaneous absorbent of neutron.
In microbiology, agar agar has growing applications. The trend of using agar agar as culture medium is developing in institute of microbiology, microbiological lab of universities and the industries that make use of microorganism. Besides, agar agar can also be used in preparation of flat culture medium that is difficult to prepare in lab and has special requirements. The application of agar agar in manufacturing agarose and preparing flat culture medium has made it possible to specialize in microbiology and biochemistry.

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Common Types of Agar

Type of Agar	Brief Description	Suitable for Student Use?
Blood Agar	Contains blood cells from an animal (e.g. a sheep); most bacteria will grow on this medium.	No, due to potential for contamination from human contact.
Chocolate Agar	Comprised of sheep blood that provides the X and V factors necessary for Haemophilus growth, this is a nutrient medium which is used in culturing fastidious organisms such as Haemophilus species and Neisseria. Chocolate agar, however, does not reveal hemolysis data, so species differentiation among the members of Haemophilus must be performed in another manner.	No, due to potential for contamination from human contact.
LB (Luria Bertani) Agar	A subtype of nutrient agar, this is the general medium for microbiology studies and may be used for routine cultivation of not particularly fastidious microorganisms. Also, does not preferentially grow one kind of bacteria over another.	Yes.
MacConkey Agar	This is an agar upon which only Gram-negative bacteria can grow. What is more is that E.coli will grow into red colonies, as there is a pH indicator present. It should be mentioned that MacConkey agar powder comes in two versions: one with the sugar lactose in it, and one without any added sugars. Since E.coli ferments sugars to acids (thus the red color), one can add one of the many different kinds of sugars to this sugar-free MacConkey agar and see if red colonies develop. If you get red colonies, you know the E.coli strain you are using can use that sugar.	No, due to selectivity.
Miller's LB Agar	This common variation of LB agar appears to have the same components as LB, just in different proportions.	Yes, but sticking with the generic formula is recommended.
Neomycin Agar	Contains the antibiotic neomycin, which found in many medications such as creams, ointments and eyedrops. Neomycin was discovered in 1949 by the microbiologist Selman Waksman, and it is produced naturally by the bacterium Streptomyces fradiae. Moreover, Neomycin has a broad spectrum of effects, killing both gram-positive and gram negative bacteria. It is relatively toxic to humans, and some people have allergic reactions to it. Often, Neomycin agar is used for culturing organisms anaerobically. Neomycin stops the growth of gram-negative bacilli and staphylcocci, allowing Streptococcus species to grow more abundantly.	No, due to safety concerns.
Non-nutrient Agar	Usually not suitable for growing bacteria. However, may be used for growing other microorganisms.	No.
Nutrient Agar	Will grow the largest number of different types of microbes - fungi and bacteria. Yet, not all bacteria can grow on these. Some find it too rich, and others find it deficient. The nutrient in this is beef broth, and some extracts from yeast.	Yes, because it does not selectively grow pathogenic bacteria.
Sabouraud Agar	Used for fungi and has a low pH that will kill most bacteria. It contains gentamicin, which is an aminoglycoside antibiotic. Gentamicin can also treat many different types of bacterial infections, particularly Gram-negative infection.	No, due to safety concerns.
Thayer-Martin Agar	Chocolate agar designed to isolate Neisseria gonorrhoeae, also known as "gonococcus," which is a species of Gram-negative bacterium responsible for the disease gonorrhoea.	No, due to potential for contamination from human contact.
Tryptic Soy Agar	A basic medium used for culturing many kinds of microorganisms. Tryptic soy agar is mainly used as an initial growth medium for the purposes of: observing colony morphology, developing a pure culture, achieving sufficient growth for further biochemical testing, and culture storage.	No, due to selectivity.
XLD Agar	Xylose lysine deoxycholate agar. It is used for the culture of stool samples, and contains two indicators. It is formulated to inhibit Gram-positive bacteria, while the growth of Gram-negative bacilli is encouraged. The colonies of lactose fermenters appear yellow.	No, due to selectivity.