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The Composition of Nutrient Agar

Agar is one of a number of different types of gelatinous substances used for cooking, and is probably the single most popular substance for laboratory experiments. Unlike other true gelatin, agar comes from plants and doesn't require the sacrifice of an animal. Additionally, it's the gelatinous medium of choice for nations that are better positioned to harvest sea crops than to grow corn-based starch on land.

  1. Applications

    • For all intents and purposes, agar is almost interchangeable with collagen-based gelatin used in cooking. Agar can solidify at anything from 90 to 104 degrees Fahrenheit and doesn't melt until it reaches about 185 degrees. This makes the substance an ideal thickener for soups and other dishes hot enough to turn other thickening agents back into a liquid. Its wide range of temperature use also makes it ideal for laboratory use, since many labs need to incubate cultures at or near a standard gelatin's melting point.

    Agar Production

    • Agar inhabits the cell walls of a number of different types of red algae (seaweed) that grow along the Asian Pacific coast and the surrounding islands. The Japanese refer to agar-containing algae as Kanten. To remove the agar from the seaweed, producers shred the kelp into strips, allow it to freeze overnight and then allow it to thaw out in the sun the next day. After repeated freezing and thawing, the strips lose water content, causing the agar to separate from the cell walls. Afterward, the strips are boiled and the agar floats free of the kelp.

    Properties and Structure

    • Agar is a two-part substance composed of agarose and agaropectin, which makes it a type of colloid. Colliods are any type of substance evenly dispersed in another substance; examples include smoke (solids dispersed in a gas), Styrofoam (gas dispersed in a solid) and agar (a liquid dispersed in a solid). Agarose, a solid linear polymer, is actually the "gelling" portion of the agar gel, and liquid agaropectin lay dissolved inside of it like the bubbles in Styrofoam.

    Nutritional Value

    • Agar doesn't really have any nutritional value, as such, primarily since it's almost indigestible by most organisms. In terms of nutrition, agar acts much like pure fiber in that it passes right through most creatures without adding any significant caloric value. It is this very property that makes agar so valuable as a clinical culturing medium; bacteria, mold and other specimens can live on it, but they can't eat it. The FDA food label for this substance reads like that of bottled water, listing agar as having zero percent fat, cholesterol, carbohydrates, protein, vitamins and minerals.

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