Moist Heat Sterilization

Moist Heat Sterilization


Mechanism of Action

  • Denaturation and coagulation of proteins

Temperature below 100oC:

  • For pasteurization of milk
  • Holder method
  • 65oC for 30 min
  • Flash Process
  • 72oC for 15 sec 
  • Pasteurization kills nearly 90% of the bacteria in milk 
  • Including the more heat resistant – Tubercle bacilli 
  • It does not kill bacterial spores. 
  • It does not kill the thermoduric bacteria. 
  • Also used for :
  • Vaccines of nonsporing bacteria
  • Serum or body fluids containing coagulable proteins.

Methylene blue Reduction test:

  • Indirect test 
  • Detection of microorganism in milk.
  • Prior to the process of pasterurization

Pasteurization of milk is determined by:

  1. Phosphatase test
  2. Alkaline Phosphatase (ALP) is an enzyme naturally present in all raw milk
  3. Used as an indicator of proper milk pasteurization.
  4. Complete pasteurization will inactivate the enzyme .
  5. Coliform count
  6. Standard plate count

Temperature at 100oC (Boiling):

  • Rolling boil
  • boiling for 5-10 minutes
  • Kill bacteria, but not spores or viruses

Steam at Atmospheric Pressure 1000C:

  • Koch or Arnold steamer is usually used the container
  • Culture media are simultaneously sterilized.
  • A single exposure of 20 min usually ensures sterilization
  • Tyndallization
  • An exposure of 100oC for 20 minutes
  • For three successive days 

Steam under pressure /Autoclave/steam sterilizer (>100oC)

  • Most effective sterilizing agent for
  • dressing
  • instruments
  • laboratory wares
  • media and pharmaceutical products
  • aqueous solutions.
  • Not for sharp instruments
  • Done at:
  • Temperature of 121oC
  • keeping chamber pressure of 15lb per square inch
  • For 15 min.
  • 126o
  • 20lbs psi
  • for 10 min
  • on 133o
  • 30 lbs psi
  • for 3 min.
  • Biological indicators
  • Spores of Bacillus stereothermophilus (Geobacillus stearothermophilus) are used.
  • Spores of Bacillus subtilis and Bacillus pumilis are also used.
Exam Question
 

Temperature below 100oC:

  • For pasteurization of milk
  • Holder method
  • 65oC for 30 min
  • Flash Process
  • 72oC for 15 sec 
  • Pasteurization kills nearly 90% of the bacteria in milk 
  • Including the more heat resistant – Tubercle bacilli 
  • It does not kill bacterial spores. 
  • It does not kill the thermoduric bacteria. 
  • Pasteurization of milk is determined by:
  1. Phosphatase test
  2. Alkaline Phosphatase (ALP) is an enzyme naturally present in all raw milk
  3. Used as an indicator of proper milk pasteurization.
  4.  Complete pasteurization will inactivate the enzyme .
  5. Coliform count
  6. Standard plate count

Steam under pressure /Autoclave/steam sterilizer (>100oC)

  • Most effective sterilizing agent for
  • dressing
  • instruments
  • laboratory wares
  • media and pharmaceutical products
  • aqueous solutions.
  • Not for sharp instruments
  • Done at:
  •  Temperature of 121oC
  • keeping chamber pressure of 15lb per square inch
  • For 15 min.
  • 126o
  • 20lbs psi
  • for 10 min
  • on 133o
  • 30 lbs psi
  • for 3 min.
  • Biological indicators
  • Spores of Bacillus stereothermophilus (Geobacillus stearothermophilus) are used.
  • Spores of Bacillus subtilis and Bacillus pumilis are also used.
Don’t Forget to Solve all the previous Year Question asked on Moist Heat Sterilization

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