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Not to be confused with auger or augur.
For other uses, see Agar (disambiguation).
Mizuyōkan - a popular Japanese red bean jelly made from agar.
A blood agar plate used to culture bacteria and diagnose infection. Agar or agar-agar is a gelatinous substance derived by boiling a polysaccharide in red algae, where it accumulates in the cell walls of agarophyte and serves as the primary structural support for the algae's cell walls. Agar is a mixture of two components: the linear polysaccharide agarose, and a heterogeneous mixture of smaller molecules called agaropectin. Throughout history into modern times, agar has been chiefly used as an ingredient in desserts throughout Asia and also as a solid substrate to contain culture medium for microbiological work. Agar (agar-agar) can be used as a laxative, an appetite suppressant, vegetarian gelatin substitute, a thickener for soups, in fruit preserves, ice cream, and other desserts, as a clarifying agent in brewing, and for sizing paper and fabrics. The gelling agent is an unbranched polysaccharide obtained from the cell walls of some species of red algae, primarily from the genera Gelidiui and Gracilaria, or seaweed (Sphaerococcus euchema). For commercial purposes, it is derived primarily from Gelidium amansii. In chemical terms, agar is a polymer made up of subunits of the sugar galactose. Contents * 1 Background * 2 Uses * 2.1 Microbiology * 2.1.1 Motility assays * 2.2 Plant biology * 2.3 Molecular biology * 2.4 Culinary * 2.5 Other uses * 3 See also * 4 References| Background
The structure of an agarose polymer.
Agar consists of a mixture of agarose and agaropectin. Agarose, the predominant component of agar, is a linear polymer, made up of the repeating monomeric unit of agarobiose. Agarobiose is a disaccharide made up of D-galactose and 3,6-anhydro-L-galactopyranose. Agaropectin is a heterogeneous mixture of smaller molecules that occur in lesser amounts. Agar exhibits hysteresis, melting at 85 °C (358 K, 185 °F) and solidifying from 32-40 °C (305-313 K, 90-104 °F). This property lends a suitable balance between easy melting and good gel stability at relatively high temperatures. Since many scientific applications require incubation at temperatures close to human body temperature (37 °C), agar is more appropriate than other solidifying agents that melt at this temperature, such as gelatin. The word "agar" comes from agar-agar, the Malay name for red algae (Gigartina, Gracilaria) from which the jelly is produced. It is also known as kanten, China grass, Japanese isinglass, Ceylon moss or Jaffna moss. Gracilaria lichenoides is specifically referred to as agal-agal or Ceylon agar. Agar was first used in microbiology in 1882 by the German microbiologist Walther Hesse, an assistant working in Robert Koch's laboratory, on the suggestion of his wife Angelina Fannie Eilshemius Hesse. He discovered that it was more useful as a solidifying agent than gelatin, due to its better solidifying temperature. Uses
100mm diameter Petri dishes containing agar jelly for bacterial culture Main article: Agar plate
Agar is used throughout the world to provide a solid surface containing medium for the growth of bacteria and fungi. Microbial growth does not destroy the gel structure because most microorganisms are unable to digest agar. Agar is typically sold commercially as a powder that can be mixed with water and prepared similarly to gelatin before use as a growth medium. Other ingredients are added to the agar to meet the nutritional needs of the microbes. Many specific formulations are available, because some microbes prefer certain environmental conditions over others. Motility assays
As a gel, an agarose medium is porous and therefore can be used to measure microorganism...