LPT 311: Milk and Milk Products Technology (1+1)

Efficiency of pasteurization

TEST FOR PASTEURISED MILK

Aschaffenburg and mullen phosphatase test

• Enzymes like peroxidase, catalase, lipase and alkaline phosphatase present in milk are destroyed by pasteurisation temperature.

Phosphatase test

• If the milk is added to a suitably buffered solution of disodium-p-nitrophenyl phosphate, this is hydrolysed by enzyme phosphatase to form p-nitrophenol which is yellow in alkaline solution. Standard disc will have numbers of 0, 6,8,10 and 42.

Buffer solution

• g of Na₂Co₃ and 1.5g of NaHco₃ are dissolved in 2 litres of distilled water.

Substrate

• Disodium–p–nitrophenyl phosphate not less than 95% pure is used for the test.

Buffer Substrate

• Transfer 0.15 g of substrate into 100 ml of measuring cylinder or in graduated flask and make up to 100^th mark with the buffer solution. It should not be stored for a long time; but can be kept in refrigerator up to one week. It should give the reading of less than 10 on the disc.

Procedure

• To 10 ml or 5 ml of buffer substrate in a test tube add 2 ml or 1 ml of milk respectively. Close the test tube with a sterile rubber stopper.
• Invert the test tube and mix gently. Prepare a blank in the same way with heated milk.
• Incubate in a water bath at 37⁰C ± 0.5⁰C for 30 minutes
• Return to the water bath and take second reading after 90 minutes. Yellow colour is read in a lovibond all purpose comparator fitted with the phosphatase disc calibrated in microgram of p-nitrophenol.
• Blank is kept on the left side of comparator and the sample on the right and the disc is rotated until the colour matches. 30 minutes test reveals serious faults in pasteurisation and 90 minutes reveals minor errors in pasteurization. Addition of even 0.1% raw milk can be detected.

Interpretation

Disc reading after 30 minutes Interpretation

• 0 to trace Properly pasteurised
• 6 Doubtful
• 10 and above Under pasteurised
• Disc reading after 2 hours Interpretation
• 0 to 10 Properly pasteurised
• Above10 Under pasteurised.

Result

 

Comment

 

Questions

1. Name the test conducted for testing the efficiency of pasteurization?
2. When does phosphatase test give false positive results?
3. Name the phosphatases present in milk and give their inactivation temperature.
4. What does the colour development indicate in the test?