Determination of Methylene Blue Reduction Time for Pasteurized Milk (MBRT Test)

Principle:
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.

 Reagent Required:

Methylene Blue Reduction Dye

 MBRT Procedure:

1. Prepare a standard methylene blue solution by dissolving one tablet of methylene blue thiocyanate in 200 ml of sterile water.
2. Add this to 10 ml of milk, shake well and keep in water bath.
3. Note the time taken for the blue color to change to white.
4. The total time gives MBRT time.

MBRT Test result and interpretations: