Tyndallization and Pasteurization
Contents
• Tyndallization
• Pasteurization
Learning objectives
At the
end of this lecture, student will be able to
– Discuss sterilization at temperature
100⁰C
– Discuss sterilization at temperature
below 100
– Explain pasteurization and
tyndallization
Thermal sterilization /
Sterilization by heat
Moist heat
sterilization / Steam sterilization
a) Sterilization at temperature above
100⁰C (Saturated stream)
– Autoclaving / steam sterilization
b) Sterilization at temperature of
100⁰C ( Boiling water)
– Tyndallisation
– Sterilization by boiling water
c) Sterilization at temperature below
100⁰C
(Hot water below Boiling Point)
– Pasteurization
– Vaccine bath
e) Heating with a bactericide
Sterilization at 100°C
- Boiling
- Steaming
- Tyndallisation
Boiling
• Boiling at 100°C for 30 minutes is
done in a water bath
• Syringes, rubber goods and surgical
instruments may be sterilized by this method
• After sterilization the materials
should be removed with forceps already sterilised by dipping in suitable
disinfectant or by heating in flame
• All bacteria and certain spores are
killed
Steaming
• Steam (100°C) is more effective than
dry heat at the same temperature as:
– Bacteria are more susceptible
to moist heat
– Steam has more penetrating power
– Steam has more sterilizing power as
more heat is given up during condensation
Steam
Sterilizer
• It works at 100°C under normal
atmospheric pressure i.e. without extra pressure
• It is ideally suitable
for sterilizing media which may be damaged at a temperature higher than
100°C
• It is a metallic vessel having 2
perforated diaphragms (Shelves), one above boiling water, and the other about
4″ above the floor
• Water is boiled by electricity, gas
or stove
• Steam passes up
• There is a small opening on the roof
of the instrument for the escape of steam
Tyndallization
• Fractional sterilization or
tyndallization is a method used to destroy bacteria and endospores
• In this articles are boiled or steamed at 212°F (100°C) for 30 min
in a pot with lid, three days in a row
• Between the boiling steps the jars
are kept warm, around 30°C to allow the remaining endospores to germinate
Principle: Any resistant endospores will germinate after
the first heating and therefore be susceptible to killing during the second and
third heating.
• Also called fractional
sterilization – A fraction is sterilized on each day
Applications
• This method is used for sterilizing
egg serum, sugar containing media and gelatin media which will be damaged at
higher temperature
Limitations
• This method is only applicable to
sloutions which bacterial spores surviving the first heating have a chance to
develop during the next 24 hours
Sterilization below 100⁰C –
Pasteurization
• Louis Pasteur found a practical method of
preventing the spoilage of beer and wine
• Pasteur used mild heating, which was
sufficient to kill the organisms that
caused the particular spoilage problem without seriously damaging the taste of
the product
• The same principle was later applied
to milk to produce what we now call pasteurized milk
• Pasteurization of milk was to
eliminate pathogenic microbes
• It lowers microbial numbers, which
prolongs milk’s good quality under refrigeration
Phosphatase test –
• To determine whether the products
have been pasteurised
• Phosphatase is an enzyme naturally
present in milk
• If the product has been pasteurised,
phosphatase will be inactivated
Procedure
• Take 1 ml of milk sample
• Put 5 ml of nitrate Phosphate buffer
solution
• Incubate it in water bath at
temperature of about 37˚C
• Check for colour change after 15
minutes
• If colour changes then the milk is
not pasteurized
Conclusion : In the image Test tube on left
side with pale yellow colour is showing test of Raw milk confirms alkaline
phosphate activity and test tube on right side is showing no colour change in
case of packed milk confirming Pasteurization
Types of Pasteurization
- Classical method of
pasteurization - High Temperature Short-time
(HTST) pasteurization / Flash method - Ultra-High-Temperature (UHT)
pasteurization
1.
Classical
method of pasteurization
·
The
milk was exposed to a temperature of about 63⁰C for 30 minutes
• The milk proteins tend to protect
the microorganisms but inspite of this mycobacterium tuberculosis is killed in
20mins but extra 10mins provides a very safe exposure which destroys the other
pathogens found in milk and the lactic acid producing organisms responsible for
souring
2. High Temperature Short-time (HTST) pasteurization
• Uses temperatures of at least 72°C,
but for only 15 seconds
• HTST pasteurization lowers total
bacterial counts, so the milk keeps well under refrigeration
3. Ultra-High-Temperature
(UHT) pasteurization
• Milk can be stored for several
months without refrigeration
• The liquid milk (or juice) is
sprayed through a nozzle into a chamber filled with high –temperature steam
under pressure
• Sterilizing temperatures are reached
almost instantaneously
• After reaching a temperature of
140°C for 4 seconds, the fluid is rapidly cooled in a vacuum chamber
Heating with a bactericide
• This method is based on the fact
that bactericides are more effective at high temperature
• This method is used in a
sterilization of aqueous solutions and suspensions that are destroyed by
autoclaving
• Suitable proportion of a bactericide
is added to the solution to be sterilized which is distributed in the final
containers and sealed
• The sealed containers are then
heated at 100⁰C in a steam sterilizer or water bath for 30 minutes.
Summary
• Pasteurization is a technique used
to destroy pathogenic organisms helps to improve the keeping qualities of food
products without affecting their taste
• Tyndallization is a process of
fractional sterilization used to sterilize heat sensitive liquids like culture
media
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