Tyndallization and Pasteurization

Tyndallization and Pasteurization




Learning objectives

At the
end of this lecture, student will be able to

      Discuss sterilization at temperature

      Discuss sterilization at temperature
below 100

      Explain pasteurization and

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)


      Sterilization by boiling water

c)       Sterilization at temperature below

                (Hot water below Boiling Point)


      Vaccine bath

e)      Heating with a bactericide

Sterilization at 100°C

  1. Boiling 

  2. Steaming

  3. Tyndallisation


       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


       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


       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

       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


       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
– A fraction is sterilized on each day


       This method is used for sterilizing
egg serum, sugar containing media and gelatin media which will be damaged at
higher temperature


       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 –

       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


       Take 1 ml of milk sample

       Put 5 ml of nitrate Phosphate buffer

       Incubate it in water bath at
temperature of about 37˚C

       Check for colour change after 15

       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

  1. Classical method of

  2. High Temperature Short-time
    (HTST) pasteurization / Flash method

  3.  Ultra-High-Temperature (UHT)

method of pasteurization

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

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

       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.


       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

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