Microbiology and Deterioration of Milk and Milk Products

Dye reduction test

• Advantages
• Simple, rapid, and inexpensive
• Only viable cells actively reduce the dyes

• Disadvantages
• Not all organisms reduce the dyes equally
• Not applicable to food specimens that contain reductive enzymes

Direct microscopic count

• Method
• Deliver 0.01 ml of milk on slide ,air dry
• Stain with LW (Levowitz- Weber )stain for 10 min.
• Count bacterial clumps with the microscope
• Reading results:
• Bacterial clump: dark blue
• Protein, Leucocytes and somatic cells :light blue background
• Fat globules : colorless
• Dirt: brown
• * clump : is one cell or group of cells of same type separated by a distance from other clumps or cells