Moist Heat Sterilization

• For pasteurization of milk
• Holder method
  • 65^oC for 30 min
• Flash Process
  • 72^oC 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:Pasteurization of milk is determined by:

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

1. Phosphatase testColiform count
   • Alkaline Phosphatase (ALP) is an enzyme naturally present in all raw milk
   • Used as an indicator of proper milk pasteurization.
   •  Complete pasteurization will inactivate the enzyme .
2. Standard plate count

Temperature at 100^oC (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 100^oC for 20 minutes
  • For three successive days 

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

• Most effective sterilizing agent for
• dressing
• instruments
• laboratory wares
• media and pharmaceutical products
• aqueous solutions.
• Not for sharp instruments

Done at:

• Temperature of 121^oC
  • keeping chamber pressure of 15lb per square inch
  • For 15 min.
• 126^oC 
  • 20lbs psi
  • for 10 min
• on 133^oC 
  • 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.