Agar
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Agar or agar-agar, is a jelly-like substance, obtained from red algae.
Contents
Composition
Agar consists of a mixture of two polysaccharides: agarose and agaropectin, with agarose making up about 70% of the mixture. Agarose is a linear polymer, made up of repeating units of agarobiose, 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, and is made up of alternating units of D-galactose and L-galactose heavily modified with acidic side-groups, such as sulfate and pyruvate.
Gelidium agar is used primarily for bacteriological plates. Gracilaria agar is used mainly in food applications.
Properties
Agar is a yellowish, beige or brown (depending on the source) gel, which dissolves slightly in water. It exhibits hysteresis, melting at 85 °C and solidifying from 32–40 °C. 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.
Availability
Agar can be bought from many food stores, as well as online.
Projects/Uses
- Food (deserts)
- Vegetarian substitute for gelatin
- Clarifying agent in brewing
- Make agar plates
- Grow microbial cultures
- Measure microorganism motility and mobility
- Make salt bridges and gel plugs
Handling
Safety
Agar is non-toxic and is used as food. You should not, however, consume lab-grade agar.
Storage
Agar should be kept in dry and clean places, to avoid rotting. A plastic bottle or bag is usually sufficient. Agar is best stored between +15°C to +25°C.
Disposal
No special disposal is required. Discard it as you wish.
