Agar, or sometimes known as agar-agar, is a gelling agent obtained from algae. They are mainly found in the cell walls of red algae and can be extracted by boiling. It is a complex sulfated polymer made up of subunits of sugar galactose, extracted from Gelidium cartilagineum, Gracilaria confervoides, and related red algae.
Agar has a composition mainly made out of two polysaccharides: agarose and agaropectin, with agarose making up about 70% of agar. Agarose is a linear polymer, made up of agarobiose monomers, which is a disaccharide consisting of D-galactose and 3,6-anhydro-L-galactopyranose. Agaropectin is a heterogeneous mixture of smaller molecules and is made up of alternating units of D-galactose and L-galactose, modified with the addition of acidic side groups such as sulfate and pyruvate.
They have a very distinctive smell and it is a common chemical used in laboratories. Agar is commonly used as a culture medium for the growth of various microorganisms. Commercially-produced agar is used in food industry as a thickener and stabilizer. It can be used as a bulk laxative, in making emulsions, and as a supporting medium for immunodiffusion and immunoelectrophoresis.
Agar which are not grinded usually occurs in bundles with thin, membranous, agglutinated strips, or in cut, flaked or granulated forms. Agar may have a light yellowish-orange appearance and sometimes may even be colorless. It is tough when wet but brittle when dry.
Powdered agar may appear white to yellowish-white or pale yellow. When using a microscope to examine powdered agar in water, it appears transparent. In chloral hydrate solution, the powdered agar looks even more transparent than it is in water.
Agar can be obtained from seaweed with hot water before freezing and thawing to purify it. Commercial extraction procedures involve washing, chemical extraction, filtration, gelation, freezing, bleaching, washing, drying, and milling.
In the food industry, agar is mainly used as a thickener and stabilizer. Agar solution is commonly used as an ingredient in desserts throughout Asia. Agar solution is used as a thickener for soups, fruit preservatives and ice creams. It can be used as a replacement to pectin in jams and gelatin in marmalades. Agar solution is used in culinary technique to clarify sauces. It is utilized in desserts, sweet jellies, puddings, cakes and various fruit salads. Approximately 80% of agar solution is fiber, hence it can be used as an intestinal regulator.
In laboratory practices, agar is commonly used as a growth medium along with other nutrients for the culturing of bacteria and fungus. It is also used as a gelating agent for the plant cell culture.