food preservation methods

1. FOOD PRESERVATION
• What is food preservation?
Retaining food over a period of time without
being contaminated by pathogenic organisms
or chemicals and without losing its colour,
texture, flavour and nutritious value.

2. Advantages:
• Increases the shelf life of food
• Retain the quality of food – colour,
• Texture, flavour & nutrition value
• Increases food supply
• Adds variety to the food
• Decreases wastage of food

3. GENERAL PRINCIPLES OF
PRESERVATION
• To destroy or inactivate micro-organisms.
• To prevent the re-entry of new microbes by
sealing food.
• To maintain the nutritive value, colour, flavour,
texture of the food as far as possible.

4. METHODS OF FOOD PRESERVATION
1.HEAT PROCESSING
2.DEHYDRATION
3.CHEMICAL PRESERVATION
4.OIL AND SPICES
5.CANNING
6.PASTEURIZATION

5. 1.HEAT PROCESSING
• All types of spoilage agents are destroyed
when subjected to high temperature
• Temperature raised to temp with spoilage
agents(enzymes, bacteria) can no longer
survive
• The product is then sterilized airtight
containers.

6. 2.DEHYDRATION
• Process of removing the moisture from
product(drying)
• Once moisture is removed from products it
can it can render growth of spoiling agents
• Eg sun drying

7. 3.CHEMICAL PRESERVATION
• Uses high concentration of salt, sugar and
acids.
• Salt used as preservative to prevent bacterial
growth in vegetables, fruits etc.
• Strong acidic medium like vinegar, lemon juice

8. 4.OIL AND SPICES
• Oil and spices along with salt and sugar are
used,they resist the activity of microbes in
food and improves flavor of food

9. 5.CANNING
• Preservation of food in a sealed containers,usually
after the application of heat,through steam under
pressure
• The product is sterilized at 135°C to 172°C for few
seconds and sealed in sealed container
• Eg.Fruit juices,sauces
• Relatively long shelf-life

10. 6.PASTEURIZATION
• Used on large scale to protect milk against
bacterial infection
• Milk is heated to min 62°C for 30 minutes,
then milk is heated to 70°C for 15 seconds
• Milk is sterilized by boiling for a period of
time.

11. PLATE FREEZING
• Food packed between flat, hollow refrigerated
metal plates.
• Press tightly on the food and reduce any air gaps.
• Used for many bulky products
• ideal for freezing large blocks of product, but
cannot easily freeze irregular shaped items
• The plates may be horizontal or vertical

12. PLATE FREEZER
• Classified into 3 types
1. Batch type
2. Semiautomatic type
3. Automatic type

13. Freezing Methods
• Quick freezing is done by using one or more of
the following ways:
• Air blast freezing
• Contact freezing
• Immersion freezing

14. 1.Immersion Freezing
• Food products dipped in low temp liquids
• Non toxic, does not affect flavor
• Produce thin ice coating on product surface
preventing food products from dehydrating
during storage

15. Immersion freezer
• The immersion freezer consists of a tank with a
cooled freezing media, such as sodium chloride,
calcium chloride and mixtures of salt and sugar.
• The product is immersed in this solution or sprayed
• fast temperature reduction through direct heat
exchange.

16. 2.AIR BLAST FREEZER
• Either still air or forced air is used.
• Air is recirculated over food at between 30ºC
and 40ºC at a velocity of 1.5–6.0 m/s.
• In batch equipment, food is stacked on trays in
rooms or cabinets.

17. 3.Contact freezing
• Product is freezed when metal surface cooled
by refrigerant like ammonia or cold brine
comes in direct contact with product.