not mine by pdst.ie

1. FOOD PRESERVATION
COMMERCIAL
PRESERVATION
© PDST Home Economics

2. COMMERCIAL
FREEZING
• Blast Freezing: Food
passed through tunnel
on conveyor belt and
cold air (-30ºC) is
blown over it. Suitable
for most food.
• Plate or Contact
Freezing: Food is
pressed between 2
cold metal surfaces.
Used for thin foods
e.g. burgers, fish
fillets or fingers,
chops.

3. COMMERCIAL FREEZING
• Flow Freezing: Food
passes through a
tunnel on a perforated
conveyor belt.
Freezing air is blown
from underneath and
freezes each piece of
food separately so
they don’t stick
together e.g. peas,
berries etc.

4. COMMERCIAL HEAT
TREATMENTS
• Canning/ Bottling, Pasteurisation, Sterilisation
and UHT

5. CANNING / BOTTLING
• Fruit, vegetables, meat, fish, soup, stew.
• Principles:
(a) Heat destroys enzymes and microbes
(b) Sealing in an airtight container prevents
recontamination.
• Method:
Preparation of food - Vegetables blanched & meat
cooked. Cans filled with food + liquid (syrup, brine,
sauce). Air removed. Air tight seal. Sterilised.
Cans cooled & labelled.

6. CANNING / BOTTLING
• High acid foods: e.g. Fruit need fast heat
treatment - 100°C for <30 min.
• Low acid foods: e.g. Meat need higher temp and
longer time - 115 °C for >30 min.
• Cans are lacquered on inside to prevent reaction
between food and metal.
• Aseptic canning :Food and cans are sterilised
separately at ultra high temperatures. The cans
are filled, sealed, cooled and labelled. High temp
means less time involved so less damage to food.
Also used for large cans of food.

7. CANNING / BOTTLING
• Don’t buy bulging, dented or rusted tins.
• Remove food from can once opened and use
quickly.
• Bottling same as canning except glass containers
used e.g. ketchup, sauces, mayonnaise.

8. COMMERCIAL CHEMICAL
PRESERVATION
• Chemical preservation means the addition of
preservatives to food to prevent enzyme and
microbial activity.
• Chemicals used are: salt, sugar, sulphur dioxide,
sorbic acid, antioxidants, alcohol and acid e.g.
vinegar.

9. PRINCIPLES OF CHEMICAL
PRESERVATION
• Most chemicals work by dissolving in water of the
food cells forming a concentrated solution.
Microbial cells are dehydrated by osmosis and die.
• Alcohol denatures the protein in the microbial
cells and destroys them.
• Acids lower the pH of the food making it an
unsuitable environment for enzyme or microbial
activity.

10. COMMERCIAL
DEHYDRATION
• Principle: Microbes need water.
Dehydration removes the water from the
food stopping microbial growth.
• Methods:
Sun drying e.g.tomatoes, Spray drying
e.g.milk, Roller drying e.g. breakfast
cereals, Accelerated freeze drying (AFD)
AFD=Food frozen @ low temp. Tiny ice
crystals then evaporated in vacuum
chamber (sublimation).
Advantages: Lightweight foods. Less heat
needed so better flavour & nutritive
value. Longer shelf life e.g. coffee, fruit,

11. (H.L) IRRADIATION
Radiation is used to destroy micro-
organisms in food
Advantages
• Destroys microbes and
other parasites.
• Longer shelf life
• Slows ripening and
sprouting
• No effect on colour,
flavour, texture
• No need for chemicals
Disadvantages
• Not suitable for high
fat food- rancidity
• Loss of vitamins
• High levels of radiation
needed for some
microbes
• Public are concerned
• May be used to disguise
poor products

12. (H.L) EFFECTS OF
PRESERVATION
Freezing
• Microbes and enzymes
inactivated
• Some loss Vit. B1 and C on
thawing
• Loss of texture especially
if frozen slowly
• Possible freezer burn
Canning
• Microbes and enzymes
destroyed
• Vit. B and C destroyed by
heat
• Food cooked
• Loss of colour, flavour &
texture
• Canning liquid affects
nutritive value- salt, fat
or sugar content

13. EFFECTS OF DRYING ON
FOOD
• Microbes destroyed
• Water removed
• Water soluble Vit. B &
C lost
• Changes in shape,
weight, colour, texture
of food