Methylene Blue Reduction Time for Milk

 

Determination of Methylene Blue Reduction Time for 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

Procedure:

1. The samples of milk are mixed thoroughly. If the milk is in a bottle/ pocket, it shall be inverted at least 25 times to mix the fat uniformly with the milk.

2. Take 10 ml of milk into a test tube and add 1 ml of standard methylene blue solution.

3. Invert the test tube to mix the milk and methylene blue solution.

4. Place the test tube in a thermostatically maintained water bath at 37⁰C and note down the time of incubation.

5. Observe the test tubes after 30 min for decolourization reduction of dye. If there is no decolourization the tubes are inverted once and transferred to the water bath for further incubation.

6. After 30 min, continue to observe for the reduction of dye at an interval of every one-hour.

7. The milk shall be regarded as decolorized, when the entire column of milk is completely decolorized or is decolorized up to 5 mm of the surface.

MBRT Test result and interpretations:

 

MBRT TEST RESULTS	MBR Time (Hrs)	Milk Quality
	5 hrs and above	Very Good
	3 – 4 hrs	Good
	1 – 2 hrs	Fair
	Half an hour	Poor

 

Grading of milk in MBR test

Quality of milk	Reduction time	Approx. keeping quality/ml	Approx. bacterial count per ml
Good	5 hour or more	40 hrs	Below 5,00,000
Fair	2 to 5  hours	30 hrs	5,00,000 to 40,00,000
Bad	20 mins to 2 hrs	10 hrs	40,00,000 to 2,00,00,000
Very bad	20 mins or less	Less than 10 hrs	Above 2,00,00,000