The Chemical Composition of the Nutrient Agar

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The Chemical Composition of the Nutrient Agar
A scientist uses a dish with a small amount of agar in it to grow an experimental culture of bacteria. (Photos.com/Photos.com/Getty Images)

Biochemists culturing microbes on the clear flat glass of a petri dish likely use a base of agar to grow the microbes. Several types of agar exist, and each has specific applications for which they are best used. Nutrient agar can be used to grow a wide variety of microorganisms; however, it is not known to grow all of them.

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Agar Comes From Algae

Agar as a substance comes from processed red-purple marine algae that grow in both California and Asia. The agar production process involves first boiling the algae, which leaves a gel-like sugar substance called galactose when cooled. Agar is most commonly associated with laboratories, which use it as a medium to grow bacteria and other microorganisms. This is because agar production produces a sterile environment for scientists to grow cultures of microorganisms to study.

Agar Nutrition Facts

Agar is less commonly known out of the laboratory as a food additive because of its thickening properties and lack of flavour. Agar, like gelatin, thickens jellies and can also thicken sauces, soups, ice cream and drinks. Agar by itself has no nutritional value, lacking calories, fat, dietary fibre, protein and carbohydrates. Agar can also be used as a treatment to fabrics and can be found in cosmetics.

Nutrient Agar Contains Beef

Nutrient agar grows the widest variety of microorganisms and fungi. For this reason, nutrient agar is considered a preferred substance for growing cultures in the laboratory. Nutrient agar is made from a combination of agar, beef extract and peptone, which derives from milk. Nutrient agar is therefore a "complex" substance, because though it is known what ingredients make it up, the exact chemical properties are unknown since there can be significant variation in what makes up beef extract.

Other Types of Agars

Several other varieties of agars exist and come from the mixture of plain agar with additional ingredients. Chocolate agar comes with the addition of sheep blood to agar. Neomycin agar contains an antibiotic and can be found in some over-the-counter creams and ointments because it kills some strains of bacteria. Sabourad agar cannot be used to grow bacteria because of its low pH; yet it is an excellent medium for growing cultures of fungi.

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