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1. DESIGN OF
PASTEURIZ ATION PROCESS
T H E R M A L P R O C E S S I N G O F F O O D S – ( 1 8 B E E S 0 2 )
B Y : N E H A S H R E E S A R AVA N A N & N I R E N J A N A . V
Unit 4 Guidelines to critical factors in thermal

2. DESIGN OF PASTEURIZATION
PROCESSES
INTRODUCTION
The pasteurization process is widely used for
the destruction of microorganisms, particularly
those causing foodborne illness. For safe and
reliable operation, the user must have a clear
understanding of the function and operation of
the process in order to implement appropriate
management controls.
Unit 4 Guidelines to critical factors in thermal processing

3. DESIGN OF PASTEURIZATION
PROCESSES
The pasteurization process must be sufficient to
eliminate the microorganisms of concern so that
they are either destroyed or cannot grow in the
final product. It is important to consider the heat
resistance of the microorganisms that are of
concern to the particular product for which the
process is being designed. There are many factors
that can influence the survival of microorganisms
in different recipe products
Unit 4 Guidelines to critical factors in thermal processing

4. FACTORS INFLUENCING SURVIVAL OF
MICRO-ORGANISMS
• Low moisture: In semi-moist foods the heat resistance of microorganisms is generally
increased, similar to in dry environments.
• Fat: Generally the presence of high fat content increases the heat resistance of
microorganisms due to the protective action of fat and the reduced moisture
environment
• Water activity: At reduced water activity levels the heat resistance of microorganisms
is generally increased, probably due to the dry conditions. It must also be noted that
the type of humectant used to reduce the water activity may result in a different D-
value when compared to the same product with the same water activity, but achieved
via a different humectant
Unit 4 Guidelines to critical factors in thermal processing

5. FACTORS INFLUENCING SURVIVAL OF
MICRO-ORGANISMS
• Salt or sugar levels: Generally the heat resistance of micro-organisms will be
increased as the sugar or salt levels increase, again due to the drying effect.
• pH: Generally the heat resistance of microorganisms will be reduced at lower
pH.
• This table takes into account of suggested pH levels of pasteurization
Unit 4 Guidelines to critical factors in thermal processing
Table of Proposed process values (F- Value) In relation to pH and carbohydrate
content of canned foods

6. FACTORS INFLUENCING SURVIVAL OF
MICRO-ORGANISMS
Unit 4 Guidelines to critical factors in thermal processing
Table of Limiting pH values below pH 4.5 for
growth of microorganisms
Menstrum*- Solvent
Fruits and juices seperated based upon their pH
range

7. MEDIUM ACID RANGE: PH 4.2–4.5
• A lowered pH value will inhibit some
microorganisms.
• However, in this pH group there is the
risk of outgrowth and spoilage from
acid tolerant heat resistant spore-
forming bacteria.
• (e.g. Bacillus and Clostridium spp.),
namely B. macerans, B. polymyxa, B.
thermoacidurans, C. tyrobutyricum, C.
butyricum and C. pasteurianum.
Unit 4 Guidelines to critical factors in thermal processing
Bacillus Polymyxa

8. ACID RANGE: PH 3.8–4.2
• Heat resistance is closely related to pH;
i.e.
• Microorganisms are less heat resistant
at lower pH values. The main spoilage
organisms in this pH category are C.
pasteurianum, C butyricum and C.
tyrobutyricum, as well as some of the
acid-tolerant aerobicspore-forming
bacteria such as B. macerans and B.
polymyxa.
Unit 4 Guidelines to critical factors in thermal processing
C. tyrobutyricum

9. HIGH ACID RANGE: PH BELOW 3.8
• The major risk in this category is from
acid-tolerant microorganisms such as
lactic acid bacteria, yeasts and moulds,
some of which can produce relatively
heat resistant ascospores (e.g.
Byssochlamys fulva and Byssochlamys
nivea).
• There is also a risk of spoilage from
thermotolerant aciduric spore-forming
bacteria (e.g. Alicyclobacillus spp.),
although this organism will not grow in
all foods
Unit 4 Guidelines to critical factors in thermal processing

10. PROCESS OF PASTEURISATION
• Pasteurization is a mild heat treatment of liquid
foods (both packaged and unpackaged) where
products are typically heated to below 100 °C.
• The heat treatment and cooling process are
designed to inhibit a phase change of the
product.
• The acidity of the food determines the
parameters (time and temperature) of the heat
treatment as well as the duration of shelf life
• Parameters also take into account nutritional
and sensory qualities that are sensitive to heat.
Unit 4 Guidelines to critical factors in thermal processing

11. PARAMETERS
• In acidic foods (pH <4.6), such as fruit juice
and beer, the heat treatments are designed to
inactivate enzymes
(pectin methylesterase and polygalacturonase in
fruit juices) and destroy spoilage microbes (yeast
and lactobacillus).
• Due to the low pH of acidic foods, pathogens are
unable to grow. The shelf-life is thereby extended
several weeks. In less acidic foods (pH >4.6), such
as milk and liquid eggs, the heat treatments are
designed to destroy pathogens and spoilage
organisms (yeast and molds).
• Not all spoilage organisms are destroyed under
pasteurization parameters, thus subsequent
refrigeration is necessary.
Unit 4 Guidelines to critical factors in thermal processing

12. TOP 4 METHODS OF MILK
PASTEURIZATION
• High Temperature Short Time. In the United States, the most common method of
pasteurization is High Temperature Short Time (HTST)
• Higher Heat Shorter Time
• Ultra High Temperature
• Ultra Pasteurized
Unit 4 Guidelines to critical factors in thermal processing

13. TOP 4 METHODS OF MILK
PASTEURIZATION
• High Temperature Short Time
In the United States, the most common method of pasteurization is High Temperature
Short Time (HTST). This method involves using metal plates and hot water to raise the
temperature of the milk to at least 161 °F (71 °C) for no less than 15 seconds, or 145 °F
(62 °C) for 30 minutes, followed by rapid cooling.
• Higher Heat Shorter Time
Similar to HTST pasteurization, Higher Heat Shorter Time (HHST) uses slightly different
equipment and higher temperatures for a shorter time. Using HHST, milk can be
anywhere from 191 °F (89 °C) – 212 °F (100 °C) for its specified time
Unit 4 Guidelines to critical factors in thermal processing

14. TOP 4 METHODS OF MILK
PASTEURIZATION
• Ultra High Temperature
Another popular method of pasteurization is Ultra High Temperature (UHT). This process
the milk using commercially sterile equipment and filling it under aseptic conditions into
sealed packaging. The milk must be heated to 280 °F (138 °C) for at least two seconds,
it down. UHT kills more bacteria (good and bad) and gives it a much longer shelf life.
need refrigeration, until opened, and is shelf stable for at least six months.
• Ultra Pasteurized
Not to be confused with UHT, Ultra Pasteurized (UP) milk is heated using commercially
but it is not considered sterile because it is not hermetically sealed. Milk is heated to
least two seconds, then rapidly cooling it down. Since the milk is not hermetically sealed,
refrigerated with an average shelf life of 30 – 90 days.
Unit 4 Guidelines to critical factors in thermal processing

15. RECOMMENDED PROCESSES FOR
ACID FOODS
• A 6-fold reduction in the microbiological load is generally used when recommending
processes for acidified foods. This is lower than the 12-fold recommendations used
with low acid foods.
• The consensus is that the lower log reductions are for two reasons:
First, the processes are based on spoilage organisms and not the lethal toxin producing
C. botulinum and
Second, there is a preservation hurdle of acidity present in the foods.
The process calculations using D-value and log reductions are the same as for acid and
high acid foods,
Unit 4 Guidelines to critical factors in thermal processing

16. RECOMMENDED PROCESSES FOR
ACID FOODS
• Some further processing guidelines (in addition to those in Table above) for products with
normal contamination loading are as follows
● For products with pH between 4.3 and 4.6 (e.g. tomato based products), the process should
be equivalent to 10 min at 93.3°C (200°F).
● For products with pH between 4.0 and 4.3, the process should be equivalent to 5 min at
93.3°C (200°F).
● For products with pH 3.7–4.2, the slowest heating spot in the container should achieve 85°C
(185°F) for at least 5 min or 95°C (203°F) for 30 s.
● For products with pH < 3.7, the slowest heating spot in the container should achieve a
minimum of 65°C (149°F) for 16.7 min or 70°C (158°F) for 2.1 min.
Unit 4 Guidelines to critical factors in thermal processing

17. THANK YOU
Unit 4 Guidelines to critical factors in thermal processing