This test is based on the principle that methyl blue (an oxidation-reduction dye or indicator) which is blue in its oxidized state, is reduced to colorless compound (leuco form) as a result of the metabolic activities of bacteria in milk. When a solution of dye is added, the organisms present in milk consume the dissolved oxygen and lower O-R potential to a level where methyl blue or similar indicators are reduced or decolorized.
Methylene Blue Reduction Dye
- Prepare a standard methylene blue solution by dissolving one tablet of methylene blue thiocyanate in 200 ml of sterile water.
- Add this to 10 ml of milk, shake well and keep in water bath.
- Note the time taken for the blue color to change to white.
- The total time gives MBRT time.
MBRT Test result and interpretations:
|5 hrs and above||Very Good|
|3 – 4 hrs||Good|
|1 – 2 hrs||Fair|
|Half an hour||Poor|