The document discusses principles of food preservation. It describes various methods used to preserve foods including physical techniques like heat and radiation that control microbial growth, chemical techniques like using salt, sugar, and preservatives to retard microbial action, and biological techniques like fermentation. It explains factors that affect microbial spoilage like pH, moisture content, temperature, and relative humidity. Various preservation methods are outlined in detail like canning, pasteurization, drying, freezing, smoking, and use of chemical preservatives. Both advantages and disadvantages of different techniques are presented. The overall aim of food preservation is to eliminate or reduce microbes and enzymes through controlling various intrinsic and extrinsic factors to increase shelf life and availability of foods.

1. PRINCIPLES OF FOOD
PRESERVATION
Dr Vandana Mahajani
1

2. Importance of food preservation
1 Elimination of microbes
2 Increasing shelf life of food
3 Making seasonal fruits available to them
throughout the year
4 Adding variety to the diet
5 Saving time and energy
6 Improving nutritional value of foods
7 Controlling prices
2

3. All foods undergo
deterioration/ spoilage
after harvest to some
degree
Role of food sciences is
to minimize negative
changes to the extent
possible
3

4. Factors affecting microbial spoilage
Intrinsic factors (Factors related
to the food itself)
Extrinsic factors
(Environmental conditions where
the food is stored)
4

5. Intrinsic factors
.pH
.Moisture content
.Water activity
.Oxidation-reduction
potential
.Physical structure of
the food
.Available nutrients
.Presence of 5

6. Extrinsic factors
.Temperature
.Relative humidity
.Gases (CO2, O2) present
.Types and numbers of
microorganisms
present in the food
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7. Principles of food preservation
Preventing entry of microbes can be done by
1 Asepsis- packaging the food in cans or airtight
containers
2 Filteration- used to filter liquids like juices water
and alcoholic beverages
3 creating conditions by which the microbes in the
food do not grow like freezing, drying etc.
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8. Microorganisms in Food
 Water availability
– in general, lower water activity inhibits microbial
growth
– water activity lowered by:
• drying
• addition of salt or sugar
– osmophilic microorganisms
• prefer high osmotic pressure
– xerophilic microorganisms
• prefer low water activity
8

9. Techniques of food preservation
1. Physical preservation- heat and radiation are
used to control the growth of microbes
2. Chemical preservation- potassium meta bi
sulphite and sodium benzoate , salt, sugar ,
lemon and vinegar are used to carry out
chemical reaction in food to retard microbial
action
3. Biological preservation- microbial growth is
encouraged so as to carry out fermentation to
preserve foods 9

10. Microorganisms in Food
 Antimicrobial substances
– coumarins – fruits and vegetables
– lysozyme – cow’s milk and eggs
– aldehydic and phenolic compounds –
herbs and spices
– allicin – garlic
– polyphenols – green and black teas
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11. Extrinsic Factors
 temperature
– lower temperatures retard microbial growth
 relative humidity
– higher levels promote microbial growth
 atmosphere
– oxygen promotes growth
– modified atmosphere packaging (MAP)
• use of shrink wrap and vacuum technologies to
package food in controlled atmospheres
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12. Methods of Food Preservation
Heat
most bacteria are killed at 82-93o
C, but
spores are not
121o
C wet heat for 15 minutes is required
to ensure sterility
high acid foods require less heat
in milk, only disease-causing organisms
are killed to reduce the severity of heat
required 12

13.  Pasteurization
– kills pathogens and substantially reduces
number of spoilage organisms
– different pasteurization procedures heat for
different lengths of time
– shorter heating times result in improved
flavor
13

14. Canning: more than 400 foods
preserved by canning
 food heated in
special containers
(retorts) to 115 °C
for 25 to 100
minutes
 kills spoilage
microbes, but not
necessarily all
microbes in food
14

15. Syrups and Brine
 Helps fill spaces between canned foods
and adds flavour to foods.
 Principle sugars used are sucrose and
dextorse
 Dilute salt solution with 1-2% salt is
used in canneries for vegetables
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16. Spoilage of canned goods
 spoilage prior to
canning
 underprocessing
 leakage of
contaminated water
into cans during
cooling process
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17. Blanching
 Hot water or
steam scald is
given.
 Drives out gases
and surface
material
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18. Preservation Techniques…...
Cold
under 10o
C, microbial growth is slow
frozen food (<-10o
C) usually does not have
any free water
frozen food also benefits from low water
activity to help protect against microbial growth
freezing may kill some, but not all
microorganisms, but growth is slowed or
stopped
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19. Food Preservation
 Low Temperature
– refrigeration at 5°C retards but does not
stop microbial growth
– microorganisms can still cause spoilage
with extended spoilage
– growth at temperatures below -10°C has
been observed
– Food should not be re-frozen after thawing
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20. Preservation Techniques…...
Drying
dehydrating food also dehydrates the
microorganisms which contain approx. 80%
moisture
Mostly used for meat, however fruits and
vegetables also dried.
Cutting veg, blanching or
scalding( inactivates the enzymes), drying
( steam, air , vaccum or inert gas) and
packing.
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21. Preservation Techniques…...
Sugar & Salt
Addition of either to a food item
increases the affinity of the food
for water, thereby removing
water from the microorganism
through osmosis
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22. Preservation Techniques…...
Acidification
acids may be in foods naturally,
produced by fermentation, or added
artificially
as pH decreases, heat required for
sterilization is reduced
Lactic acid fermentation used in
preparation of cheese ripening, corn,
pickles, peas, beans, olives
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23. Preservation Techniques…...
Smoke
Contains formaldehyde and other
preservatives
Heat will help reduce microbial
populations and somewhat dries
the food
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24. Preservation Techniques…...
Atmosphere
Exclude air (O2) for control of
aerobes
Provide air (O2) for control of
anaerobes
Add CO2
Add N2
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25. Food Preservation
 Removal of Microorganisms
– usually achieved by filtration
– commonly used for water, beer, wine,
juices, soft drinks, and other liquids
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26. Chemical preservatives
 Propionates of calcium and sodium
 Added to dough to prevent growth of
mould and increase shelf life of food
 Sorbates potassium salt of sorbic acids
added to acidic food to control growth of
fungi or yeasts in apple juice. Wrappers
of cheese also made of this.
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27.  Benzoates used to preserve acid
products just like sorbates
 Citric, lactic, acetic and phosphoric
acids. They are used a s acidulants in
food . Acetic acid and lactic acids have
the greatest preserving power
 Sodium chloride salt is added to presrve
meats specially
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28. Food Irrdaiation
 One of the beneficial applications of
atomic energy
 It involves controlled application of
energy from gamma rays, X rays, and
accelerated electrons
 Low doses (.15 kilo Gray) can prevent
sprouting of potatoes and onions
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29. Methods of preservation
Advantages
1. Drying
Concentrated form of food
Inhibits microbes
Retains nutrients
2. Smoking
Partly by drying and partly by
incorporation of certain substances
3 Refrigeration
Slows microbial action
Slows action of enzymes
4 Freezing
Prevents microbial growth and
availability of water
Good retention of nutrients
5. Adding salt and sugar
Makes water unavailable
Does not destroy nutrients
Helps in preservation
Disadvantages
Loss of thaimine and Vit C
SO2 is added to retain some
nutrients , but some individuals
may be sensitive to these.
Eating smoked is liked with some
cancers in some parts of the world
Slow loss of some nutrients with time
Blanching of veges prior to freezing
may cause loss of Vit B and C
Increases salt and sugar content of
the food
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30. Advantages
6. High heat processing
Eg. Pasteurisation
Deactivates enzymes
Destroys micro organisms
7. Canning
Destroys microbes and enzymes
8. Chemical preservatives
Prevent microbial growth
No loss of nutrients
9. Ionising radiation
Steralizes food without changing
flavours like spicies.
Inhibits sprouting of potatoes
Increases life of food like strawberries
and mushrooms
Disadvantages
Loss of hest sensitive nutrients
Water soluble Vitamins may be lost
due to liquid present in the can used
for preservation
Some people are sensitive to some
preservatives
Longer shelf life of foods
Can lead to greater loss of nutrients
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