Food preservation using heat treatment methods. Brief introduction of methods such as blanching, canning, frying, sterilization and pasteurization

1. FOOD PRESERVATION BY
HEAT TREATMENTS

2. FOOD
PRESERVATION
Food Preservation is the process of
treating and handling food in such a way
that it :
❏ Maintains the nutritional value, texture
and flavor of the food.
❏ Prevents food and vegetables from
getting spoiled.
❏ Increases the shelf life of the food
product.
❏ Decreases food wastage.
❏ Makes food available throughout the
year.

3. PRINCIPLES OF FOOD PRESERVATION
Prevention or delay of microbial decomposition
❏ By keeping out microorganisms (asepsis).
❏ By removal of microorganisms.
❏ By hindering the growth and activity of microorganisms (eg. by low
temperatures, drying, anaerobic conditions, or chemicals).
❏ By killing the microorganisms (by heat or radiation).
Prevention or delay of self decomposition of the food.
❏ By destruction or inactivation of food enzymes ( by blanching).
❏ By prevention or delay of chemical reactions (by using antioxidant).
Protection against insects, rodents, and animal infestation

4. THERMAL PROCESSES
Thermal processing is defined as the combination of
temperature and time required to eliminate a desired
number of microorganisms from a food product.
"Thermal" refers to processes involving heat
Heating food is an effective way of preserving.
The basic purpose for the thermal processing of foods
is,
❏ Reduces or destroy microbial activity.
❏ Reduces or destroy enzyme activity.
❏ Makes the food meet a certain quality standard.

5. TYPES OF
THERMAL
PROCESSING
❏ BLANCHING (at about 100o C)
❏ PASTEURIZATION (below 100o
C)
❏ STERILIZATION (above 100o C)
❏ CANNING
MILD PROCESSES -BLANCHING
AND STERILIZATION
SEVERE PROCESSES -
CANNING, BAKING,
ROASTING, FRYING

6. MILD HEAT
TREATMENT
SEVERE HEAT
TREATMENT
❏ Kills pathogens and
inactivates enzymes.
❏ Advantage -Minimal damage
to flavour, texture and
nutritional quality.
❏ Disadvantage -Short shelf
life.
❏ Examples -Pasteurization,
Blanching
❏ Kills all bacteria.
❏ Advantage -Long shelf life
❏ Disadvantage -Major
changes in texture, flavor
and quality.
❏ Examples -Canning

7. STERILIZATION
❏ A controlled heating process used to completely eliminate all
living microorganisms, including thermoresistant spores in milk
or other food.
❏ It can be achieved by moist heat, dry heat, filtration, irradiation,
or by chemical methods.
❏ Used to treat all types of food products such as milk, juices,
beer and many others.
❏ Various time/temperature combinations are applied, depending
on the product properties and shelf-life requirements.

8. Sterilization with moist heat:
Temperatures generally range from 110 to 130°C with
sterilization times being from 20 - 40 min.
Sterilization with dry heat:
For killing bacterial endospores by dry heat, longer
exposure times (e.g. up to 2 hours) and higher
temperatures (e.g. 160 – 180°C) are required than with
moist heat.
Sterilization by chemical means:
Chemical means may also be applied. Ethylene oxide is
used to sterilize food, plastics, glassware, and other
equipment.

9. PASTEURIZATION
❏ Temperature applied is below 100o C.
❏ The heating may be by means of steam, dry heat or electric
currents and the products are cooled promptly after the heat
treatments.
❏ It can be used to destroy relatively heat sensitive
microorganisms.
(Named after Louis Pasteur)
❏ Pasteurization is a process of heat processing a liquids or a
food to kill pathogenic bacteria to make the food safe to eat.
This process is named after Louis Pasteur.

10. TYPES OF PASTEURIZATION
Low Temperature Low Time
(LTLT)
LTLT is heating food to
a
low temperature for a
long
tim
e
-62.8°C for 30
minute
Also called the
Holding/
Batch
method.
Ultra HIgh Temperature
( UHT)
Ultra-high-temperature
(UHT)
pasteurization
involves
heating milk or cream to
138°
to 150° C (280° to 302° F) for
one or two
seconds.
Packaged in sterile,
sealed
containers, UHT milk may
be
stored without
refrigeration
for
months.
High Temperature Short Time
(HTST)
HTST is heating food to
a
high temp and maintain for
a
short
time:
-71.7°C for 15
second
Also called the
Continuous/
Flash
method.

11. Effects of Pasteurization
Positive effects of pasteurization :
● Destruction of pathogenic microorganisms.
● Increases the safety of market milk for human
consumption.
● Improves keeping quality and inactivation of
certain naturally occurring enzymes.
The negative effects of pasteurization:
● It also destroys the beneficial bacteria and other
essential nutritions.
● There is small loss of native aroma particularly in
case of fruit juices.

12. PASTEURIZATION STERILIZATION
1. Partial destruction of
microorganism.
2. Temperature below 100oC.
3.Minimum damage to flavor,
nutritional quality and texture.
4. Short shelf life.
5.Another preservation method has to
be used such as refrigeration/ freezing.
Complete destruction of
microorganism.
Temperature 100o C and above.
Major changes in flavor,
nutritional quality and texture.
Long shelf life.
No other method required.

13. CANNING
❏ Preservation of food in sealed containers
followed by application of heat treatment.
❏ Prevents microbial contamination and
inactivates degradative enzymes.
❏ Oxidation may occur in food resulting in
change in color and flavour of food and
also reducing the nutrient content.
❏ Is done in tin cans, glass containers,
aluminium and plastic pouches
❏ Done at high temperature and high
pressure. 116 -121’

14. FOODS THAT ARE CANNED
Low Acid Foods -Meat, fish, poultry, dairy, which fall into a pH range of 5 to 6.8. These foods don’t have enough
acid to stop bacteria from forming.
Acid Foods -pH range between 3.7 and 4.5. Fruits such as pear, oranges, tomatoes fall in this class.These foods
have enough acid within themselves naturally, they don’t require a higher temperature to kill bacteria.
High Acid Foods -pH value range from 2.3 to 3.7. (Pickled products and fermented foods, also jams, and jellies.)

15. TYPES OF CANNING
Water-Bath Canning
❏ Also referred as hot water
canning.Boiling water bath.
❏ Uses a large kettle of boiling
water.
❏ Filled jars are submerged in the
water and heated to an internal
temperature of 212°F for a specific
period of time.
❏ This method is used for processing
high-acid foods, such as fruit,
items made from fruit, pickles,
pickled food, and tomatoes.
Pressure Canning
❏ Pressure canning uses a large kettle
that produces steam in a locked
compartment
❏ The filled jars in the kettle reach an
internal temperature of -240 °C
under a specific pressure that is
measured with a dial gauge or
weighted gauge on the
pressure-canner cover.
❏ A pressure canner should be used
for processing vegetables and
other
low-acid foods, such as meat,
poultry and fish.

16. BLANCHING
● Blanching is a slight heat treatment, using hot water or steam applied mostly to vegetables.
● Time duration of 30-60 seconds.
● Retains color, texture, flavor, and nutritional content of fruits and vegetables.
● Keeps the outer surface soft and gives the inner surface a little crisp.
● Stops the enzymatic reactions that take place within the fruits and vegetables and help to
preserve them for a longer time.
● Complete immersion of fruits and vegetables is done within high simmering water for a few
minutes and then placed in an ice bath to instantly cool them.
There are three major steps in the blanching process.
1. Preheating
2. Blanching
3. Cooling

18. REFERENCES
❏ ANON. 1982. Canned Foods: Principles of Thermal Process Control, Acidification and Container Closure
Evaluation. 4th ed. The Food Processors Institute, Washington, D.C.
❏ BALL, C. O. and OLSON, F. C. W. 1975. Sterilization in Food Technology. McGraw-Hill, New York.
❏ DESROSIER, N. W. and DESROSIER, J. N. 1977. Technology of Food Preservation. 4th ed. AVI Publishing
Co., Westport, Conn.
❏ LOPEZ, A. 1981. A Complete Course in Canning. 11th ed. Books 1 and 2. The Canning Trade, Baltimore.
❏ Potter N.N. (1986) Heat Preservation and Processing. In: Food Science. Springer, Dordrecht.
❏ Kanemitsu et al. (May 2005). "A comparative study of ethylene oxide gas, hydrogen peroxide gas plasma, and
low-temperature steam formaldehyde sterilization".
❏ Molins RA (2001). Food irradiation: principles and applications.
❏ M.N. Ramesh,2003. Encyclopedia of Food Sciences and Nutrition (Second Edition).

19. THANK YOU