A General Account of Food Preservation Techniques

1. FOOD PRESERVATION TECHNIQUES
Dr Saji Mariam George
Associate Professor
Assumption College Autonomous
Changanacherry

2. FOOD PRESERVATION TECHNIQUES
Food preservation – the process of prevention
of decay and spoilage of food.
• Increase the shelf life of food
• Make the seasonal food available through
out the year
• Add variety to the diet
• Save time by reducing preparation time and
energy
• Stabilizes prices of food
• Increase the availability of food – improve
the nutrition of the people.

3. Method varies with the length of storage intended.
1. DEHYDRATION(DRYING OR DESICCATION)
• Removal of water from the food
• Food containing 10% or less of free moisture are
not subjected to spoilage by microbes – unable
to grow .
• Dehydrated food → keep in air -tight containers-
not exposed to fluctuations in humidity.

4. a). SUNDRYING
• Heat from Sun is used for drying
• Materials prepared by suitable methods
are placed on shallow trays in sunlight.
e.g. Raw Mango, Raisins, Dates , Figs,
Tapioca chips , Bitter gourd & Chilly
“kondattams” , Pappad , Fish, Meat,
Prawns, Grains etc.

5. b). SMOKING
Food dried by exposing them to smoke by burning
special wood - mahogany, apple, walnut etc.
• Heat from smoke helps in removal of moisture
• Exposure to smoke imparts a characteristic flavour.
• Certain bactericidal substances may be formed
during smoking ( formaldehyde, phenols, cresols)
and this also helps in preserving the food to a
limited extent.
E.g. – Fish, Meat (esp. Beef)

6. c). MECHANICAL DRYING
• Temperature and humidity are controlled
• Products with superior quality, better colour,
correct texture and right flavour can be obtained.
i) Dehydrators
Food materials are spread in thin layers on metal
trays and inserted in the dehydrator and dried by
heat.
E.g. - Pappad, Green peas, Potato, Jack fruit etc.

7. ii) Roller dryers
• Finely ground wet suspension of food is spread as a thin
layer on a revolving drum which is heated.
• Dry powder is then scrapped off and packed.
iii) Spray dryers
• Food in the form of a liquid or a finely ground
suspension is pumped through a fine jet and falls as a
fine spray into a chamber through which hot air is
circulated.
• The fine droplets of the liquid quickly lose their
moisture by evapouration and fall on the floor of the
chamber as a fine powder.
e.g. Instant coffee, tea, milk powder, gelatin etc.

8. d). Salting
• Binding moisture by addition of salt – prevents
growth of microbes
• Salt produces high osmotic pressure and causes
destruction of microorganisms by plasmolysis.
• Dry salting is used in the preservation of
Tamarind
Raw mango
Fish
Meat etc.

9. e). Pickling
• A very common food preservation technique
• Right amount of salt, chilly, turmeric , asafoetida , oil.
Vinegar etc. used in pickling helps to preserve food.
• A layer of oil on top - prevents the growth of moulds and
yeasts by preventing exposure to air.

10. f). Adding sugar
• High concentration of sugar binds moisture in the food –
water is unavailable for microbes to grow .
e.g Jam
Jelly
Marmalade (using orange)
Sweetened condensed milk.

11. g) Freeze Drying (Lyophilization)
• Food is preserved by rapid freezing and dehydration of the
frozen material under high vacuum.
• Food is preserved in its natural state - no loss of texture
/flavour
• Food is packed in plastic or Aluminium foil packets in an
atmosphere of Nitrogen
Used for the preservation of
• Meat
• Poultry
• Sea foods
• Fruits
• Vegetables.

12. 2. USE OF CHEMICAL PRESERVATIVES & FOOD
ADDITIVES
Food additive- a substance or mixture of
substances added to food
• Preservatives
• Colours
• Flavouring agents
• Antioxidants
• Emulsifying & stabilizing agents
• Antibiotics etc.

13. Chemical preservatives
• A food additive - arrest or prevent spoilage
by microbes
i) Citric acid
• To increase acidity and prevent mould
growth - fruit squash, jams, jellies
• To flavour extracts, candies
• To adjust pH to 5 – Fish
• To prevent discolouration - Crab meat
• As a dip to delay browning – sliced
Peaches.

14. ii) Benzoic acid & its salts
Effective to inhibit the growth of bacteria,
yeasts & moulds
Sodium benzoate is used in
• Jams
• Jellies
• Carbonated beverages
• Fruit juices etc.

15. iii) Sorbic acid & its salts (Calcium, Sodium &
Potassium salts)
• Effective against moulds, yeasts and many
bacteria.
• Used as a direct antimicrobial additive in foods
• As a spray, dip or coating on packaging
materials
• To prevent refermentation and souring of wine
– A combination of 225 ± 25 mg Potassium
sorbate and a 30 ± 10 mg free SO2 prevent
refermentation and souring of wine.

16. Widely used in bakery & confectionary
products –
 Cakes
 Fillings for chocolate
 Cheese
 Beverages
 Dried fruits
 Bread
 Fruit juice
 Jellies
 Jams etc.

17. iv) Acetates - derivatives of Acetic acid –
Vinegar (4% Acetic acid), Sodium diacetate
More effective against yeasts and bacteria
than moulds.
• Vinegar is used in pickles, Mayonnaise etc.
• Sodium diacetate is used in cheese spreads
• As a treatment for wrappers for butter .

18. v) Sulphur dioxide & sulphites(Potassium
metabisulphite,
Sodium metabisulphite)
SO2 – used to treat drying fruits, molasses
Sulphites – added to wine as preservative
Potassium metabisulphite is used in canning

19. vi) Nitrites & Nitrates (Sodium & Potassium
salts)
• Inhibitory effect on bacterial growth.
• Inhibit the formation of Clostridium botulinum and
Staphylococcus aureus
• Used in meat and fish preservation
• For the retention of red colour of meat.
vii) Propionic acid & propionates
Sodium & Calcium propionates
• Used to prevent mould in sliced bread
• For preservation of cheese

20. viii) Salicylic acid & Salicylates
• Used to preserve fruits and vegetables
ix) Antioxidants
Used to prevent oxidation of fats and oils which
causes rancidity (Development of unpleasant
odour)
Egs Butylated Hydroxy Anisole (BHA)
Butylated Hydroxy Toluene(BHT)

21. x) Antibiotics- Aureomycin (Chlortetracyclins),
Terramycin (Oxytetracyclins), Chloromycetin
(Chloramphenicol)
Inhibit protein synthesis
Used to length storage time at chilling
temperatures – meat, fish, poultry etc.

22. 3. Preservation by use of low temperature
• Microbial growth and enzyme reaction are retarded in
foods stored at low temperature.
a) Cellar storage (Temperature about 15 ° C)
• Storage in cellars(underground rooms) slows down
the decomposition.
• Can be stored for limited periods during winter
months.
Eg - Root crops
Potato
Onion
Apple
Cabbage

23. b) Refrigeration or Chilling treatment
( Temperature 0 °C – 5 ° C)
• Retard the growth and metabolic activities of
microbes
• Can be stored for a few days
• Fruits
• Vegetables
• Meat
• Poultry
• Milk
• Fish
• Egg
• Prepared Food.

24. c) Freezing (Temperature, - 18 °C to – 40 ° C)
• The growth of microbes and enzyme activity
are reduced to the minimum.
• Can be stored for long periods – a few weeks
to months .
• Before freezing, vegetables are given
blanching (mild heat treatment, above 80
°C)to inactivate the enzymes .

25. Quick freezing – at temperatures between -18
°C to – 34 ° C for 30 minutes or less
• Maintain the identity and freshness when
they are thawed(brought to room
temperature) because very small ice crystals
are formed during quick freezing.
Vegetables
Fruits (Strawberry)
Meat
Sea foods
Mushrooms etc.

26. 4. Preservation by use of high temperature
• Most reliable and safest method
• High heat coagulate proteins and inactivate
the enzymes of microbes → destruction
a)Pasteurisation (Temperature below 100 °C)
• Brief exposures to moderately high
temperatures to reduce the number of viable
microorganisms and kill the pathogenic
microorganisms.

27. • Used where drastic heat treatment may
cause undesirable changes in the food
• Usually supplemented by other methods –
sudden cooling and keeping in refrigeration
to prolong shelf life.

28. i) High Temperature Short Time (HTST)
Method
Milk is heated to 72 °C for 15 seconds and
rapidly cooled to 10 °C and kept under
refrigerated conditions – inhibits the growth
of organisms that may have survived.
ii) Low Temperature Long Time (LTLT) Method
Milk is heated to 62.8 °C for 30 minutes
followed by sudden cooling to 10 °C and
kept under refrigerated conditions.

29. USES OF PASTEURISATION
• Preservation of milk and other dairy products
• Beer
• Fruit juices
• Aerated drinks
• Dried fruits –Raisins , Apricots, Dates etc.
• Grape wine –pasteurized at 81 °C - 85 °C for 1
minute
• Grape juice at 76.7 °C for 30 minutes.

30. b)Boiling( Temperature 100 °C)
• Kills the vegetative cells and spores of yeasts
and moulds
• Kills only the vegetative cells of bacteria.
• Cooked food can be preserved from 12 – 24 hrs
at room temperature, esp. on winter months.
• Cooking of rice
• Vegetables
• Milk
• Meat
• Fish

31. c)Canning( Temperature above 100 °C; Steam
under pressure , 121 °C)
Discovered by Francois Nicolas Appert (1809) –
Appertization.
• Most widely used method
• Exposure to high temperature for longer periods
– kill endospore -forming bacteria.
Steam under pressure(Pressure cooker or
autoclave)
• Most effective method – kills vegetative cells
and spores
• Heating to high temperature is followed by rapid
cooling

32. Canning Process
i) Cleaning – Select high quality materials and
clean –fresh vegetables, fruits, meat etc.
ii) Blanching – in hot water or in steam – kills
microbes, fixes natural colour, removes air
within product and inactivates enzymes.
iii) Filling of cans or jars –Hot food is filled into
cans
(tin cans →made of tin –coated steel, glass
containers, flexible pouches, plastic bags,
Aluminium cans → used only for products that
do not require high vacuum or high temperature
processing such as beer, frozen fruits and juice
concentrates, cheese etc.)

33. iv) Autoclaving
• Cans → steam under pressure
• Duration depends on load - more time for
heavily loaded.
• Non-acid foods →116 -121 °C at lbs/psi
pressure for 1 -2 hours.
• Meat require more time
• Acid foods require only immersion of cans in
boiling water.

34. v) Cooling
• Autoclaved cans are immediately cooled → prevent
undesirable changes in texture and flavour due to
overcooking.
5. Preservation of food by creating anaerobic conditions.
Prevent the growth of aerobes
a) Vacuum filling- food materials are packed in
impermeable plastic material and the air is sucked
out to create vacuum.
Used for Nuts- to reduce loss of flavour due to
oxidation
Meat
Cheese etc.

35. b) Modified atmosphere packaging
• Enclosure of food in a package in which the
atmosphere is changed by altering the
proportions of Carbon dioxide, Oxygen,
Nitrogen ,water vapour and trace gases.
• Retards microbial and biochemical activity.
• Salad crops are packaged in sealed bags with
an atmosphere modified to reduce Oxygen
concentration and increase carbon dioxide
concentration.
• Can be used to increase the shelf life of
bacon, red meat, poultry, vegetables etc.

36. 6. Food Preservation by radiation (Cold sterilization – the
product is not heated)
• Approved only in a very limited way.
• Mainly used for spices and condiments
• Reduces the number of microbes and insects – replaces
the chemicals used for this purpose.
• Inhibits sprouting in Potato, Onion, Garlic etc.
• Delays ripening in Banana, Avocado, Papaya, Guava etc.
• UV rays are the most widely used – for the treatment of
water for beverage and knives for slicing bread, sanitizing
eating utensils etc.
• Gamma rays are also used.
• Irradiated food materials – meat, fish, poultry etc. can be
stored at room temperature without spoilage.

37. 7. Use of anti-sprouting chemicals
• Increases shelf life in root crops , tubers etc. –
Potato, Carrot, Onion etc.
E.g. Maleic hydrazide is used as an anti-
sprouting agent for Potato.

38. THANK YOU