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
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3. All foods undergo
deterioration/ spoilage
after harvest to some
degree
Role of food sciences is
to minimize negative
changes to the extent
possible
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4. Factors affecting microbial spoilage
Intrinsic factors (Factors related
to the food itself)
Extrinsic factors
(Environmental conditions where
the food is stored)
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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
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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
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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
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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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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
30