Microbiology and Deterioration of Milk and Milk Products

Viable count method

• Advantages

• Can see cell morphology
• Count viable cell only
• Can be used to different types of samples ( milk, milk products

• Disadvantages

• Take long time
• Lots of tubes , tedious.

Dye reduction test

• A quick test for determination of microbial load of milk
• Use Methylene blue or resazurin dyes
• Add 1ml of dye to 10ml of milk, incubate 1 hr at 36c
• If there is change in color , it means high bact. Load .It is not good quality milk, shorten expiration date.
• If no change in color (still blue), low bact. Load , good quality milk , expand expiration period
• A long history of use in the dairy industry, especially to measure microbial quality from raw milk