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�CONCEPT OF STERILIZATION AND STERILIZATION METHODS

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CONTENTS

TYNDALLIZATION
PASTEURIZATION

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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

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THERMAL STERILIZATION / STERILIZATION BY HEAT

MOIST HEAT STERILIZATION / STEAM STERILIZATION

STERILIZATION AT TEMPERATURE ABOVE 100⁰C (SATURATED STREAM)

AUTOCLAVING / STEAM STERILIZATION

STERILIZATION AT TEMPERATURE OF 100⁰C ( BOILING WATER)

TYNDALLISATION
STERILIZATION BY BOILING WATER

STERILIZATION AT TEMPERATURE BELOW 100⁰C

(HOT WATER BELOW BOILING POINT)

PASTEURIZATION
VACCINE BATH

HEATING WITH A BACTERICIDE

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STERILIZATION AT 100°C

BOILING
STEAMING
TYNDALLISATION

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STERILIZATION AT 100°C -

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

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STERILIZATION AT 100°C

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

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STERILIZATION AT 100°C

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

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STEAM STERILIZER

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

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STERILIZATION AT 100°C�TYNDALLIZATION

FRACTIONAL STERILIZATION OR TYNDALLIZATION IS A METHOD USED TO DESTROY BACTERIA AND ENDOSPORES

John Tyndall

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TYNDALLIZATION

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

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TYNDALLIZATION

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

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TYNDALLIZATION

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

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STERILIZATION BELOW 100⁰C - PASTEURIZATION

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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

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PASTEURIZATION

PASTEURIZATION OF MILK WAS TO ELIMINATE PATHOGENIC MICROBES
IT LOWERS MICROBIAL NUMBERS, WHICH PROLONGS MILK'S GOOD QUALITY UNDER REFRIGERATION

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PASTEURIZATION

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

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PHOSPHATASE TEST

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

Pasteurization

©M. S. Ramaiah University of Applied Sciences

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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

Pasteurization

©M. S. Ramaiah University of Applied Sciences

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TYPES OF PASTEURIZATION

CLASSICAL METHOD OF PASTEURIZATION
HIGH TEMPERATURE SHORT-TIME (HTST) PASTEURIZATION / FLASH METHOD
ULTRA-HIGH-TEMPERATURE (UHT) PASTEURIZATION

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TYPES OF PASTEURIZATION

CLASSICAL METHOD OF PASTEURIZATION
THE MILK WAS EXPOSED TO A TEMPERATURE OF ABOUT 63⁰C FOR 30 MINUTES

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PASTEURIZATION MACHINE

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AGITATORS

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TYPES OF PASTEURIZATION

CLASSICAL METHOD OF PASTEURIZATION
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

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TYPES OF PASTEURIZATION

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

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TYPES OF PASTEURIZATION

HIGH TEMPERATURE SHORT-TIME (HTST) PASTEURIZATION /

FLASH METHOD

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High Temperature Short-time (HTST) pasteurization

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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

Types of Pasteurization

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ULTRA-HIGH-TEMPERATURE

(UHT) PASTEURIZATION

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

Types of Pasteurization

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Ultra-high-temperature (UHT) pasteurization

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HTST VS.UHT PASTEURIZATION

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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.

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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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