Enzymatic Test for Milk by Methylene Blue Reductase Test

PRACTICAL 3: ENZYMATIC TEST FOR MILK BY METHYLENE BLUE REDUCTASE TEST

Introduction:

This test recommended determining the quality of milk sample. It is based on the population of the bacteria with that dissolved oxygen. If the sample contains large population of actively metabolizing microorganisms, the concentration of dissolved oxygen will low because of presence of enormous number of microorganisms.

The dye methylene blue is an indicator of such reaction. In an anaerobic environment, the color of dye would be dull and said to be reduced. The raw milk contains large number of enteric organisms and Streptoccocus lactis.Both are dye reducers. The rate of duration at which color of the dye is reduced indicated quality of milk.

Objective:

To become familiar with an enzymatic test to determine the quality of a milk sample.

Materials:

* Milk sample (A- pasteurized milk, B- unpasteurized milk)

* Test tubes

* Methylene blue

* Pipettes

* Water bath

* Glass marker

Completion time: 2 hours

Complication: none

Procedure

1. Methylene blue reagent are prepared.

2. 10 ml of sample milk are transferred to two test tubes.

3. 1 ml of methylene blue reagent are added to each tubes.

4. The tubes are shacked and placed in a water bath

5. The samples are observed every 10 minutes to 60 minutes and the time are recorded. The period of reduction are calculated.

6. The quality of milk is determined.

Results:

Time | Observation |

| Pasteurized | Unpasteurized |

10 minute | Light blue | Light blue |

20 minute | Light blue | Slightly dark blue |

30 minute | Light blue | 2 layers of dark blue and clear |

40 minute | Light blue | 2 layers of dark blue and light blue |

50 minute | Light blue | 2 layers of dark blue and light blue |

60 minute | Light blue | 2 layers of dark blue and light blue |

Discussion:

The methylene blue reduction test is based on the fact that the colour imparted to milk by...