Analysis Of Milk

Quantitative Analysis Of Milk By Standard Plate Count (Spc) Method

APHA (American Public Health Association) recommends the standard plate count as the official method in its milk Ordinance and Code. Actually the presence of human pathogenic bacteria may arise due to unsanitary handling of milk, diseased udder, or improper storage conditions. The increase in number of bacterial counts has the more possibility of transmission of diseases.

Requirements

• Milk sample
• Sterile water
• Petri plates
• Pipettes
• Nutrient agar
• Incubator
• Colony counter

Procedure

1. Procure raw milk samples
2. Dilute the sample of milk in sterile distilled water for the isolation of microorganisms from soil/water
3. Transfer 1 ml milk serially in sterile distilled water to make dilution: 1:100, 1:10,000,
4. 1:10,00,000.
5. Transfer 0.1 ml and 1 ml of the milk from each diluted sample bottle into two separate Petri plates, and pour sterilised nutrient agar medium into each plate.
6. After the nutrient agar has solidified, incubate the plates at 35ºC for 24 to 48 hours.
7. As stated in serial dilution technique, count the plates containing 30 to 300 colonies for
8. calculating the number of organisms per millilitre of the original milk sample.
9. Prepare a smear of the milk film and observe for the presence of bacteria.

Results

The microscopic appearance gives type and arrangement of bacterial cells. Count the number of bacterial colonies per Petri dishes, take average of three plates and estimate CFUs per ml of milk.

Reference

Dr. R. C. Dubey – Practical Microbiology