Food preservation involves preventing the spoilage of food and allowing it to be stored for future use. There are several methods of food preservation including low temperatures like refrigeration and freezing, high temperatures like pasteurization and canning, drying foods, using high concentrations of salt or sugar, chemical preservatives, radiation, and aseptic packaging. Each method aims to inhibit microbial growth and enzymatic reactions in order to prolong the shelf life of foods.

1. Food Preservation
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2. Definition
• Food preservation can be
defined as the science that
deals with the process of
prevention of spoilage of
food, thus allowing it to be
stored in a fit condition for
future use.
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3. • Preservation of food increase the shelf
life of the food.
• Foods are preserved at home or in
commercial settings to prolong their
shelf life and to use particular foods
like vegetables & fruits when not in
season.
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4. Principles of food preservation
1. Prevention or delay microbial decomposition
• Keeping out microorganism or removing the
microorganisms already present. ( Asepsis)
• By removal of microorganism ( Filtration)
• By hindering the growth and activity of
microorganism ( Refrigeration ,
Dehydration and addition of chemical in
food ) ASTHA K. PATEL 4

5. • By killing microorganism ( Boiling &
Radiation)
2. Prevention or delay of self-decompoition of
food
• By destruction of enzymes
• By prevention or delay of chemical
reaction.
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6. Types ofFoodpreservation
Use of low temperatures
Use of high temperature
Canning procedures
Drying method
High concentration of sugar & salts
Preservation by Chemical
Preservation by Radiation
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7. I. Low temperatureMethod
• Microbial growth & enzyme reaction are
retarded in food stored in low temperature.
Cellar storage (15 C)
Refrigerator or chilling
( 0-5 C)
Freezing (-18 to -40 C)
1. Slow Freezing,
2. Quick Freezing
3. Hydrofreezing
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8. 1. CellarStorageTemperature
• Food is stored in cellars ( Under ground
rooms) in many villages where the temp. is
lower than 15 C.
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9. Root crops, potatoes, onions, apples &
other similar foods can be stored for
limited periods during the winter
months.
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10. 2. Refrigerator orChillingMethod
• These temp. are obtained & maintained by means of
ice & refrigerator.
• Fruits, vegetables, meat,
Poultry, milk & its product,
fish, eggs can be preserved
from two days to a week
when held at this temp.
• Food prepared for serving or
left overs may also be stored in
the household refrigerator.
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11. • Commercial cold storage are now used throughout
the country for the storage of food products.
• This made such food available throughout the year.
• Low temp. inhibit growth of Microorganism.
• Freezing may results in destruction of some
microorganism
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12. 3. Freezingmethod
• Freezing may preserve food for long periods of
time.
• Some microorganisms are destroyed during
freezing.
• The chief preservative effects of freezing
temperature is inability of Microorganisms to
grow at freezing temperature.
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13. A. Slowfreezing
• Also known as Sharp Freezing.
• Used in Home Freezers.
• Temp. - “-4 to -29 C”
• Time duration – 3 – 72 hours
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14. B. QuickFreezing
• Large quantity of food can be frozen in short
period of time.
• Temp. – “-32 to -40 C”
• This method freeze foods do rapidly that fine
crystals are formed.
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15. C.Dehydrofreezing
• It consist of drying the food & then freezing it to
preserve.
• The quality of Dehydro Frozen fruits & vegetables is
equal to that of fruit & vegetables frozen without
drying.
• Cost in packing, freezing, storing & shipping is less
because reduction in weight & volumes.
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16. II. High TemperatureMethod
• The destruction of Micr4oorganisms by heat.
Pasteurisation
Heating temp. about 100 C
Heating above 100 C
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17. 1. Pasteurization
Most of organisms are killed during heating,
A few survive & hence, their growth must be
inhibited by low temp.
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18. Two methods for pasteurization
HTST Method
(High Temp Short
Time)
High temp.
used for short
time.
heated at 72 DC for 15
seconds.
Heated at 150 DC .. Time
required is 1 or 2 seconds
Flash
Method
LTLT
(Low Temp.
long Time)
Low temp.
used for
long time.
heated at 63
DC for 30
minutes.
Holder
Method
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19. 2. Heating up to temp. about 100 C
• Most method of cooking under this.
• It temp. can be obtained by boiling any liquid
food.
• This method kills all bacteria except spores.
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20. 3. Heating above100 C
• Temp. above 100 C is obtained by means of
steam under pressure, as in a pressure cooker
or autoclave.
• Sterilization of foods can be brought about
121 C for 15 minutes.
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21. III. Canning Methods
Cleaning
Blanching
Exhausting
Sealing the container
Sterilizing the sealed container
Cooling the container
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22. 1. Cleaning
• First step of canning
• On large scale cleaning is done with the help
of various kinds of washers.
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23. 2. Blanching
• Immersion of raw food materials, especially
vegetables & fruits into hot water or exposure
to live steam.
• It serve as an additional hot water wash.
• It softens fibrous plant tissue, inhibit action of
enzyme & fix natural colour of product.
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24. 3. Exhausting
• Gases are expelled by passing the open can,
containing food through an exhaust box in
which hot water or steam is used to expand
the food & expel air & other gases from the
contents.
• After the gases are expelled, the can is
immediately sealed, heat processed & cooled.
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25. 4. Sealingthe container
• Each container must be sealed properly before
it is subjected to heat process.
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26. 5. Sterilizingthe sealed container
• To prevent spoilage of food by
microorganisms.
• Sterilized by steam under pressure.
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27. 6. Cooling the container
• Can should be cooled rapidly.
• Done by air or water.
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28. IV. DryingMethod/Dehydration
• Microorganisms need moisture to grow.
• When exposed to sunlight or subjected to
dehydration, the moisture in the food is
removed.
• This prevents the growth of Microorganisms &
thereby prevent spoilage of food.
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29. Sun drying
Slow process
Many Indian
food are
preserved by
Sun drying.
Mechanical
drying
Drying of food
by heated air
Expensive
method
Spray
drying
Milk & eggs are
dried to a
powder by spray
drying
Liquid is
atomized &
sprayed into hot
air steam for
drying.
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30. Foam mat
drying
Used in orange &
tomatoes juices
Stabilizer is added in
liquid & stiff foam is
produced by
whipping.
Foam is spread in
thin layer & dried in
steam of hot air.
Drying by
osmosis
Fish is dried by this
methods.
In this method
moisture is drawn
out from all cell
tissues.
Freeze
drying
Removal of water by
freezing
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32. V. Highconcentration ofSugar & salt
• Sugar & salt aid in the preservation of food
products.
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33. 1. Salting& Pickling
• This method has been practiced since
ancient times.
• Salt is a good natural preservative, and
it is used with other spices in pickling,
ex. – mango, lemon, ginger, fish and
vegetables.
• The salt added to the vegetables draws
out water and sugar from the
vegetables. ASTHA K. PATEL 33

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35. 2. Vinegar
• It is a common preservative as it
contains acetic acid.
• It is used to preserve onions &
lemons.
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36. 3. Sugars
• Fruits are preserved
by placing them in sugar syrup.
• When bacteria, yeasts or moulds
are placed in heavy sugar syrup,
water in the cells move through
the membrane into the
concentrated syrup through
osmosis.
• Ex- jam, jelly, fruit juices.
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37. VI. Chemicalpreservation
• Only a few chemical are permitted in
prescribed minimum levels for preserving
food.
• Ex. – sodium benzoate, sorbic acid,
sodium and calcium propionate &
sulphur dioxide.
• Sorbic acid is added to cheese.
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38. Acid
• Citric acid and phosphoric acid is
added to soft drinks.
• Food such as tomatoes, citrus juices
and apples contain natural acidity.
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39. VII. Preservationby Radiation
• Micro organism are inactivated by different
kinds of radiation.
• Foods are usually irradiated with iodizing
radiation.
• Spices, vegetables and fruits, pork and
poultry are all preserved by radiation.
• Irradiation cause changes in flavor, color,
texture and nutritive value.
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40. Smoke
• Smoke contains preservative chemicals
such as formaldehyde and other
materials from burning wood.
• Smoke generates heat which kills
microorganism.
• The heat tends to dry out the food
which further helps in preservation
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41. Asepsis
• It is usually done during packaging of
foods to delay or to prevent microbial
decomposition.
• Ex. Milk and milk products are
packaged in a special food grade plastic
covers or wraps to avoid contamination
of micro organism.
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42. Freezing & Refrigeration
• Oldest method of food preservation
• Freezing – storage of food at
temperatures ranging from -2 to +16
degree Celsius.
• Commercial and house hold
refrigeration temperature
are usually between 4.5 to 7 d.c.
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43. • This method of freezing and
refrigeration is better method of food
preservation as it has less adverse
effects on taste, texture, & nutritive
value of food compared to heat
treatment, dehydration and radiation.
• Meat, fish, and fruits and vegetables
are commonly preserved in this method.
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44. Dehydration
• Water is removed from food for
preservation.
• The term food preservation refers to
artificial drying under controlled
conditions that cause minimum or no
other changes in food properties.
• Ex. – dried milk, potato flakes &
instant coffee. ASTHA K. PATEL 44

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46. Heat
• Bacteria , yeast and moulds grow best
in temp. range of about 16-38 DC.
• At the temp. – 82-93 DC most
bacteria's killed.
• When food in high acid content, such as
tomato juices or orange juice, the heat
is only used for a shorter period of
time as the killing power of heat inn
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