Explain Procedure for Determination of the Quality of Milk?

1. Prepare methylene blue solution by dissolving 1 mg methylene blue in 250 ml of sterile distilled water.

2. After thorough mixing, transfer 10 ml of each sample into labeled sterile screw cap test tubes and add 1 ml of methylene blue in each tube. For control, take 10 ml boiled milk of each sample and add 1ml of methylene blue (positive control). Negative control contains 10 ml of milk sample and 1 ml of the water.

3. Close the tubes with stoppers and mix the content of the tubes by inverting the tubes gently for 4-5 times.

4. Incubate the tubes in a water bath at 37°C for 6-8 hours. Observe the tubes for reduction of methylene blue (i.e. change in colour) after every half an hour for 6-8 hours. Compare the sample tube with positive and negative control for change in methylene blue colour.

Record the time of dye reduction and accordingly assess the quality of the milk samples.