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Pasteurization
Syeda Rubeena Fatima
Thermal death
time
• Time taken to kill a
specific microorganism at specific
temp
• Spores are killed at absolute TDT
• D is the time taken to kill 90% of
the viable spores
Heat treatment
for preserving
foods
• Temp & time used in heat processing effects food
quality and microbes present in it
• Foods lie milk and peas can be heated to a limited
extend while corn or pumpkin can undergo rigorous
heating.
History
• Louis Pasteur (December 27, 1822 – September 28, 1895) • Was born in Dole,
France. • Was a French biologist, microbiologist and chemist. • He was well known
for his discoveries of the principles of vaccination, microbial fermentation and
pasteurization. • He is remembered for his remarkable breakthrough in the causes
and prevention of diseases. • His discoveries have saved many lives ever since.
• In 1860s French wine industry was in trouble due to wine spoilage. • At that time
Pasteur was working at the University of Lille. • Pasteur examined spoiled wine
under microscope. • He finally reached that conclusion of Microorganisms similar to
the bacteria responsible for lactic acid and acetic acid fermentations. • Pasteur then
discovered that a brief heating at 55-60°C would destroy these microorganisms and
can preserve wine for long periods. • In 1886 German chemist F. Soxhlet adapted
the technique for preserving milk and reduce milk transmissible diseases.
Pasteurization
• Pasteurization is a relatively mild heat treatment, in which food is heated to below 100ºC.
• It may be by means of steam, hot water, dry heat or electric currents and the products are
cooled.
• In low acid foods (pH>4.5, for example milk) it is used to minimize the hazards from
pathogenic micro-organisms and to extend the shelf life of foods for several days.
• In acidic foods (pH< 4.5, for example bottled fruit) it is used to extend the shelf life for several
months by destruction of pathogenic microorganism and enzyme inactivation.
• In this method minimal changes are caused to sensory characteristics or nutritive value.
• The extent of the heat treatment required to stabilize the food.
• This is determined by the D value of the most heat- resistant micro-
organism
• For example milk pasteurisation - 12 logarithmic cycle number (12D)
reduction of C. burnetii
• liquid whole egg is treated to produce 9D reduction in numbers of S.
seftenberg.
• Flavours, colours and vitamins of the pasteurized food product also
determined by D values.
Different Methods of Pasteurization
Estimation of Pathogenic Micro Organism in
Pasteurization
• Phosphatase activity test is simple test. Specially for milk pasteurization.
– If phosphatase activity is found, it is assumed that the heat treatment was
inadequate to destroy the pathogenic bacteria or
– Unpasteurized milk has contaminated the pasteurized product.
• A similar test for the effectiveness of liquid-egg pasteurization is based on residual -
amylase activity.
Pasteurization of Packaged Foods
• Some liquid foods are pasteurised after filling into containers.
– Example => beers and fruit juices
• Hot water is normally used to packaged food.
• To reduce the risk of thermal shock of the container, (fracture caused
by rapid changes in temperature).
– Keep maximum temperature differences between the container
and water are 20ºC for heating and 10ºC for cooling.
• Finally packaged food is cooled to approximately 40ºC
– to evaporate surface water that help to minimize external corrosion to the container and
– to accelerate the label adhesives.
• Hot-water pasteurizers may be batch or continuous operation.
• The batch equipment consists a water bath.
– packaged food are heated to a set temperature and held this to required length of time.
– Cold water is pumped in to cool the product.
• The continuous version consists a long narrow conveyor belt to carry containers through
heating and cooling sections.
Packaged Food -
Tunnel pasteurizer
• Tunnel divided into a number of heating zones.
• Very fine hot water sprays are used to heat the
container
– Packaged food pass through each zone of the
conveyer. ( 1st & 2nd per heater, pasteurizer)
– Incrementally rises in temperature until
pasteurization is achieved.
• Cool water spray is used to cool the containers
through the tunnel.
• Temperatures in the heating zones are gradually
increased by reducing the amount of air in the
steam–air mixtures.
Pasteurization of Unpackaged Food
• Two main heat exchangers is commonly used for unpackaged food pasteurization.
1. Plate heat exchangers
2. Tubular heat exchangers
• Large scale pasteurization of low viscosity liquids,
– milk, milk products, fruit juices, liquid egg, beers and wines
– usually treated through Plate heat exchangers.
• Food is sprayed into a vacuum chamber and dissolved air is removed by a vacuum pump, prior to
pasteurization
01. Plate heat exchanger
• Food is pumped from a balance tank to a ‘regeneration’
section.
– where it is pre-heated by food that has already been
pasteurized.
• It is then heated to pasteurizing temperature in a heating
section.
– Hold until achieve the pasteurization temperature.
• If the pasteurizing temperature is not reached,
– flow diversion valve automatically returns the food to the
balance tank to be re-pasteurized.
• The pasteurized product is then cooled in the regeneration
section. And – then further cooled by cold water. – If
necessary, chilled water also use in the cooling section.
• If the pasteurising temperature is not reached – a flow
diversion valve automatically returns food to balance tank
to be re-pasteurised
Advantages of heat exchangers (HE)
• Advantages of HEs over in-bottle processing:
– more uniform heat treatment
– simpler equipment & lower maintenance costs
– lower space & labour costs
– greater flexibility for different products
– greater control over pasteurization conditions.
Concentric tube HE
• For more viscous foods; • dairy products,
mayonnaise, tomato ketchup & baby
foods.
• Number of concentric stainless steel coils •
each made from double- or triple-walled
tube.
• Food passes through the tube • heating
or cooling water is re-circulated through the
tube walls.
• Liquid food is passed from one coil to next
for heating & cooling
• heat is regenerated to reduce energy costs.
• Pasteurized food is immediately filled into
bottles& sealed.
Shell and tubular or multi-tube heat exchanger
• Important and so widely used in modern food
processing industries.
• Multi-tubular heat exchanger - Liquid food
product pass through the multi tube chamber.
• Outer tube carrying heating liquid to opposite
direction of liquid food. – Heating medium hot
steam or hot water.
• This flow direction is called as “ counter flow”.
• Counter flow direction is more efficient method
than parallel flow method. Cooling with chilled
water or brine ( counter flow)
• Multi-tubular heat exchanger is well
efficient method compare with
single tubular heater.
– Heating surface area of food is
high
– Complete and time
efficiency pasteurization. (No cold
point effect)
– Retention of more sensory
characters ( aroma, flavour).
• To increase heat absorption
efficient, the outer tubular
chamber insulate with heat
resistant materials.(reduce heat
loss to environment)
• Tubular heat exchanger can be
cleaned by through methods
(usually 1 % HNO3 and 1
% NaOH).
Effect on foods
• Pasteurization is,
– mild heat treatment
– minor changes to nutritional and sensorial characteristics
• shelf life: few days or weeks
• Effect: Colour, flavour and aroma
• Fruit juices
– Main problem is colour deterioration by enzymic browning (poly phenol
oxidase).
– This browning reaction promoted by the presence of oxygen.
– In fruit juice industries, fruits are involve to de- aerated prior to pasteurization
process.
There for retain natural fruit colour.
• Whiteness of raw milk & pasteurised milk differs
– due to homogenisation Pasteurization has no measurable effect on
– the colour of milk.
• Pigments in plant & animal products are mostly unaffected.
• Small loss of volatile aroma compounds during pasteurization of juices. Volatile
recovery used to produce high quality juices.
• Effect: Vitamin loss
• In fruit juices,
– losses of vitamin C & carotene are minimized
• Changes to milk,
– 5% loss of serum proteins &
– small changes to vitamin content.

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Pasteurization (3).pptx

  • 2. Thermal death time • Time taken to kill a specific microorganism at specific temp • Spores are killed at absolute TDT • D is the time taken to kill 90% of the viable spores
  • 3. Heat treatment for preserving foods • Temp & time used in heat processing effects food quality and microbes present in it • Foods lie milk and peas can be heated to a limited extend while corn or pumpkin can undergo rigorous heating.
  • 4. History • Louis Pasteur (December 27, 1822 – September 28, 1895) • Was born in Dole, France. • Was a French biologist, microbiologist and chemist. • He was well known for his discoveries of the principles of vaccination, microbial fermentation and pasteurization. • He is remembered for his remarkable breakthrough in the causes and prevention of diseases. • His discoveries have saved many lives ever since. • In 1860s French wine industry was in trouble due to wine spoilage. • At that time Pasteur was working at the University of Lille. • Pasteur examined spoiled wine under microscope. • He finally reached that conclusion of Microorganisms similar to the bacteria responsible for lactic acid and acetic acid fermentations. • Pasteur then discovered that a brief heating at 55-60°C would destroy these microorganisms and can preserve wine for long periods. • In 1886 German chemist F. Soxhlet adapted the technique for preserving milk and reduce milk transmissible diseases.
  • 5. Pasteurization • Pasteurization is a relatively mild heat treatment, in which food is heated to below 100ºC. • It may be by means of steam, hot water, dry heat or electric currents and the products are cooled. • In low acid foods (pH>4.5, for example milk) it is used to minimize the hazards from pathogenic micro-organisms and to extend the shelf life of foods for several days. • In acidic foods (pH< 4.5, for example bottled fruit) it is used to extend the shelf life for several months by destruction of pathogenic microorganism and enzyme inactivation. • In this method minimal changes are caused to sensory characteristics or nutritive value.
  • 6. • The extent of the heat treatment required to stabilize the food. • This is determined by the D value of the most heat- resistant micro- organism • For example milk pasteurisation - 12 logarithmic cycle number (12D) reduction of C. burnetii • liquid whole egg is treated to produce 9D reduction in numbers of S. seftenberg. • Flavours, colours and vitamins of the pasteurized food product also determined by D values.
  • 7. Different Methods of Pasteurization
  • 8.
  • 9. Estimation of Pathogenic Micro Organism in Pasteurization • Phosphatase activity test is simple test. Specially for milk pasteurization. – If phosphatase activity is found, it is assumed that the heat treatment was inadequate to destroy the pathogenic bacteria or – Unpasteurized milk has contaminated the pasteurized product. • A similar test for the effectiveness of liquid-egg pasteurization is based on residual - amylase activity.
  • 10.
  • 11.
  • 12. Pasteurization of Packaged Foods • Some liquid foods are pasteurised after filling into containers. – Example => beers and fruit juices • Hot water is normally used to packaged food. • To reduce the risk of thermal shock of the container, (fracture caused by rapid changes in temperature). – Keep maximum temperature differences between the container and water are 20ºC for heating and 10ºC for cooling.
  • 13. • Finally packaged food is cooled to approximately 40ºC – to evaporate surface water that help to minimize external corrosion to the container and – to accelerate the label adhesives. • Hot-water pasteurizers may be batch or continuous operation. • The batch equipment consists a water bath. – packaged food are heated to a set temperature and held this to required length of time. – Cold water is pumped in to cool the product. • The continuous version consists a long narrow conveyor belt to carry containers through heating and cooling sections.
  • 14. Packaged Food - Tunnel pasteurizer • Tunnel divided into a number of heating zones. • Very fine hot water sprays are used to heat the container – Packaged food pass through each zone of the conveyer. ( 1st & 2nd per heater, pasteurizer) – Incrementally rises in temperature until pasteurization is achieved. • Cool water spray is used to cool the containers through the tunnel. • Temperatures in the heating zones are gradually increased by reducing the amount of air in the steam–air mixtures.
  • 15. Pasteurization of Unpackaged Food • Two main heat exchangers is commonly used for unpackaged food pasteurization. 1. Plate heat exchangers 2. Tubular heat exchangers • Large scale pasteurization of low viscosity liquids, – milk, milk products, fruit juices, liquid egg, beers and wines – usually treated through Plate heat exchangers. • Food is sprayed into a vacuum chamber and dissolved air is removed by a vacuum pump, prior to pasteurization
  • 16. 01. Plate heat exchanger • Food is pumped from a balance tank to a ‘regeneration’ section. – where it is pre-heated by food that has already been pasteurized. • It is then heated to pasteurizing temperature in a heating section. – Hold until achieve the pasteurization temperature. • If the pasteurizing temperature is not reached, – flow diversion valve automatically returns the food to the balance tank to be re-pasteurized. • The pasteurized product is then cooled in the regeneration section. And – then further cooled by cold water. – If necessary, chilled water also use in the cooling section. • If the pasteurising temperature is not reached – a flow diversion valve automatically returns food to balance tank to be re-pasteurised
  • 17. Advantages of heat exchangers (HE) • Advantages of HEs over in-bottle processing: – more uniform heat treatment – simpler equipment & lower maintenance costs – lower space & labour costs – greater flexibility for different products – greater control over pasteurization conditions.
  • 18. Concentric tube HE • For more viscous foods; • dairy products, mayonnaise, tomato ketchup & baby foods. • Number of concentric stainless steel coils • each made from double- or triple-walled tube. • Food passes through the tube • heating or cooling water is re-circulated through the tube walls. • Liquid food is passed from one coil to next for heating & cooling • heat is regenerated to reduce energy costs. • Pasteurized food is immediately filled into bottles& sealed.
  • 19. Shell and tubular or multi-tube heat exchanger • Important and so widely used in modern food processing industries. • Multi-tubular heat exchanger - Liquid food product pass through the multi tube chamber. • Outer tube carrying heating liquid to opposite direction of liquid food. – Heating medium hot steam or hot water. • This flow direction is called as “ counter flow”. • Counter flow direction is more efficient method than parallel flow method. Cooling with chilled water or brine ( counter flow)
  • 20. • Multi-tubular heat exchanger is well efficient method compare with single tubular heater. – Heating surface area of food is high – Complete and time efficiency pasteurization. (No cold point effect) – Retention of more sensory characters ( aroma, flavour). • To increase heat absorption efficient, the outer tubular chamber insulate with heat resistant materials.(reduce heat loss to environment) • Tubular heat exchanger can be cleaned by through methods (usually 1 % HNO3 and 1 % NaOH).
  • 21. Effect on foods • Pasteurization is, – mild heat treatment – minor changes to nutritional and sensorial characteristics • shelf life: few days or weeks • Effect: Colour, flavour and aroma • Fruit juices – Main problem is colour deterioration by enzymic browning (poly phenol oxidase). – This browning reaction promoted by the presence of oxygen. – In fruit juice industries, fruits are involve to de- aerated prior to pasteurization process. There for retain natural fruit colour.
  • 22. • Whiteness of raw milk & pasteurised milk differs – due to homogenisation Pasteurization has no measurable effect on – the colour of milk. • Pigments in plant & animal products are mostly unaffected. • Small loss of volatile aroma compounds during pasteurization of juices. Volatile recovery used to produce high quality juices. • Effect: Vitamin loss • In fruit juices, – losses of vitamin C & carotene are minimized • Changes to milk, – 5% loss of serum proteins & – small changes to vitamin content.