Dextrose Salt Agar is prepared according to the standard formula 31 of the International Dairy Federation (1). It is used for enumeration of yeasts and molds in butter and other dairy products (2, 3).
Yeast extract and dextrose provide growth nutrients. A 2.5 gm sample of chilled butter is diluted with 5 ml of quarter strength Ringers solution. Plates are poured by addition of 0.2 ml of the solution, which corresponds to 0.1 gm butter. Plates are incubated at 30°C for 2 days. If growth is not visible then incubation is continued at 30°C for 3 days and visible colonies of yeasts and molds are counted.
Storage and Shelf-life:
Store below 30°C in tightly closed container and the prepared medium at 2 - 8°C. Use before expiry date on the label.
References:
1. International Dairy Federation, 1964, International Standard FIL-1 DF31 Brussels.
2. Ritter and Eschmann, 1966, Alimenta., 5:43.
3. Ritter and Eschmann, 1966, Alimenta., 5:46