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DICHLORAN GLYCEROL AGAR BASE

A selective low water activity (aW) medium for xerophilic moulds in low moisture and intermediate moisture foods. Conforms with Australian Standard Methods.

$65.00 — $159.00

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Dichloran-glycerol Agar Base was formulated by Hocking and Pitt,1,2 to fulfil the need for a suitable medium of low water activity (aW 0.95) to isolate fungal flora from dried and semi-dried foods such as cereals, nuts, condiments, dried fruits, confectionary, and dried meat and fish products. The medium conforms with Australian Standard Method AS 1766.2.2-1997.3

Traditionally, sodium chloride has been used to lower water activity in media used for the enumeration of xerophilic moulds and in 1946, Christensen published his formulation for Malt Salt Agar (MSA) containing 7.5% wt/wt salt and 2% malt extract. Other formulations utilising glucose and sucrose have been described, but MSA has been more popular, due to crystallisation and viscosity problems. MSA medium has some disadvantages. In the presence of low water activity, and the absence of an inhibitory agent, Eurotium species grow rapidly, overgrowing moulds with slower growth and smaller colonies. The low pH (4.0-5.0) of MSA combined with high levels of malt and salt, result in a soft medium, difficult to inoculate by the spread-plate technique.

Pitt and Hocking demonstrated the advantages of using glycerol as an alternative to sugars or salt. It is less viscous than sugar solutions, does not crystallise and agars containing glycerol set firmly, producing a clear, transparent agar. They also experimented with dichloran in the medium, to restrict the growth of Eurotium species, and designated the name of Dichloran-glycerol Agar to the new medium. Chlortetracycline was incorporated to restrict bacterial flora.


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